Rollup merge of #77808 - Nicholas-Baron:fn_ctxt_impl, r=matthewjasper

Moved the main `impl` for FnCtxt to its own file.

Resolves #77085 without breaking the API of the `FnCtxt` struct.

This is a solution to the file length being over 3000 (see issue #60302).

The other solution to the file length is
1. to change the API of this struct by
2. encapulating certain fields of the struct into other structs.

6 files changed, 3272 insertions, 3201 deletions

diff --git a/compiler/rustc_typeck/src/check/fn_ctxt.rs b/compiler/rustc_typeck/src/check/fn_ctxt.rs
deleted file mode 100644
index 79d6c7dbfda..00000000000
--- a/compiler/rustc_typeck/src/check/fn_ctxt.rs
+++ /dev/null
@@ -1,3200 +0,0 @@
-// ignore-tidy-filelength
-// FIXME: This file seems to have too much functionality wrapped into it,
-// leading to it being too long.
-// Splitting this file may involve abstracting functionality into other files.
-
-use super::callee::{self, DeferredCallResolution};
-use super::coercion::{CoerceMany, DynamicCoerceMany};
-use super::method::{self, MethodCallee, SelfSource};
-use super::Expectation::*;
-use super::TupleArgumentsFlag::*;
-use super::{
-    potentially_plural_count, struct_span_err, BreakableCtxt, Diverges, EnclosingBreakables,
-    Expectation, FallbackMode, Inherited, LocalTy, Needs, TupleArgumentsFlag, UnsafetyState,
-};
-use crate::astconv::{
-    AstConv, ExplicitLateBound, GenericArgCountMismatch, GenericArgCountResult, PathSeg,
-};
-
-use rustc_ast as ast;
-use rustc_ast::util::parser::ExprPrecedence;
-use rustc_data_structures::captures::Captures;
-use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::ErrorReported;
-use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticId};
-use rustc_hir as hir;
-use rustc_hir::def::{CtorOf, DefKind, Res};
-use rustc_hir::def_id::DefId;
-use rustc_hir::lang_items::LangItem;
-use rustc_hir::{ExprKind, GenericArg, ItemKind, Node, QPath};
-use rustc_infer::infer::canonical::{Canonical, OriginalQueryValues, QueryResponse};
-use rustc_infer::infer::error_reporting::TypeAnnotationNeeded::E0282;
-use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use rustc_infer::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
-use rustc_infer::infer::{self, InferOk, InferResult};
-use rustc_middle::hir::map::blocks::FnLikeNode;
-use rustc_middle::ty::adjustment::{
-    Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability,
-};
-use rustc_middle::ty::fold::TypeFoldable;
-use rustc_middle::ty::subst::{
-    self, GenericArgKind, InternalSubsts, Subst, SubstsRef, UserSelfTy, UserSubsts,
-};
-use rustc_middle::ty::{
-    self, AdtKind, CanonicalUserType, Const, DefIdTree, GenericParamDefKind, ToPolyTraitRef,
-    ToPredicate, Ty, TyCtxt, UserType,
-};
-use rustc_session::{lint, Session};
-use rustc_span::hygiene::DesugaringKind;
-use rustc_span::source_map::{original_sp, DUMMY_SP};
-use rustc_span::symbol::{kw, sym, Ident};
-use rustc_span::{self, BytePos, MultiSpan, Span};
-use rustc_trait_selection::infer::InferCtxtExt as _;
-use rustc_trait_selection::opaque_types::InferCtxtExt as _;
-use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
-use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
-use rustc_trait_selection::traits::{
-    self, ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt,
-};
-
-use std::cell::{Cell, RefCell};
-use std::collections::hash_map::Entry;
-use std::iter;
-use std::mem::replace;
-use std::ops::Deref;
-use std::slice;
-
-pub struct FnCtxt<'a, 'tcx> {
-    pub(super) body_id: hir::HirId,
-
-    /// The parameter environment used for proving trait obligations
-    /// in this function. This can change when we descend into
-    /// closures (as they bring new things into scope), hence it is
-    /// not part of `Inherited` (as of the time of this writing,
-    /// closures do not yet change the environment, but they will
-    /// eventually).
-    pub(super) param_env: ty::ParamEnv<'tcx>,
-
-    /// Number of errors that had been reported when we started
-    /// checking this function. On exit, if we find that *more* errors
-    /// have been reported, we will skip regionck and other work that
-    /// expects the types within the function to be consistent.
-    // FIXME(matthewjasper) This should not exist, and it's not correct
-    // if type checking is run in parallel.
-    err_count_on_creation: usize,
-
-    /// If `Some`, this stores coercion information for returned
-    /// expressions. If `None`, this is in a context where return is
-    /// inappropriate, such as a const expression.
-    ///
-    /// This is a `RefCell<DynamicCoerceMany>`, which means that we
-    /// can track all the return expressions and then use them to
-    /// compute a useful coercion from the set, similar to a match
-    /// expression or other branching context. You can use methods
-    /// like `expected_ty` to access the declared return type (if
-    /// any).
-    pub(super) ret_coercion: Option<RefCell<DynamicCoerceMany<'tcx>>>,
-
-    pub(super) ret_coercion_impl_trait: Option<Ty<'tcx>>,
-
-    pub(super) ret_type_span: Option<Span>,
-
-    /// Used exclusively to reduce cost of advanced evaluation used for
-    /// more helpful diagnostics.
-    pub(super) in_tail_expr: bool,
-
-    /// First span of a return site that we find. Used in error messages.
-    pub(super) ret_coercion_span: RefCell<Option<Span>>,
-
-    pub(super) resume_yield_tys: Option<(Ty<'tcx>, Ty<'tcx>)>,
-
-    pub(super) ps: RefCell<UnsafetyState>,
-
-    /// Whether the last checked node generates a divergence (e.g.,
-    /// `return` will set this to `Always`). In general, when entering
-    /// an expression or other node in the tree, the initial value
-    /// indicates whether prior parts of the containing expression may
-    /// have diverged. It is then typically set to `Maybe` (and the
-    /// old value remembered) for processing the subparts of the
-    /// current expression. As each subpart is processed, they may set
-    /// the flag to `Always`, etc. Finally, at the end, we take the
-    /// result and "union" it with the original value, so that when we
-    /// return the flag indicates if any subpart of the parent
-    /// expression (up to and including this part) has diverged. So,
-    /// if you read it after evaluating a subexpression `X`, the value
-    /// you get indicates whether any subexpression that was
-    /// evaluating up to and including `X` diverged.
-    ///
-    /// We currently use this flag only for diagnostic purposes:
-    ///
-    /// - To warn about unreachable code: if, after processing a
-    ///   sub-expression but before we have applied the effects of the
-    ///   current node, we see that the flag is set to `Always`, we
-    ///   can issue a warning. This corresponds to something like
-    ///   `foo(return)`; we warn on the `foo()` expression. (We then
-    ///   update the flag to `WarnedAlways` to suppress duplicate
-    ///   reports.) Similarly, if we traverse to a fresh statement (or
-    ///   tail expression) from a `Always` setting, we will issue a
-    ///   warning. This corresponds to something like `{return;
-    ///   foo();}` or `{return; 22}`, where we would warn on the
-    ///   `foo()` or `22`.
-    ///
-    /// An expression represents dead code if, after checking it,
-    /// the diverges flag is set to something other than `Maybe`.
-    pub(super) diverges: Cell<Diverges>,
-
-    /// Whether any child nodes have any type errors.
-    pub(super) has_errors: Cell<bool>,
-
-    pub(super) enclosing_breakables: RefCell<EnclosingBreakables<'tcx>>,
-
-    pub(super) inh: &'a Inherited<'a, 'tcx>,
-}
-
-impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
-    pub fn new(
-        inh: &'a Inherited<'a, 'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        body_id: hir::HirId,
-    ) -> FnCtxt<'a, 'tcx> {
-        FnCtxt {
-            body_id,
-            param_env,
-            err_count_on_creation: inh.tcx.sess.err_count(),
-            ret_coercion: None,
-            ret_coercion_impl_trait: None,
-            ret_type_span: None,
-            in_tail_expr: false,
-            ret_coercion_span: RefCell::new(None),
-            resume_yield_tys: None,
-            ps: RefCell::new(UnsafetyState::function(hir::Unsafety::Normal, hir::CRATE_HIR_ID)),
-            diverges: Cell::new(Diverges::Maybe),
-            has_errors: Cell::new(false),
-            enclosing_breakables: RefCell::new(EnclosingBreakables {
-                stack: Vec::new(),
-                by_id: Default::default(),
-            }),
-            inh,
-        }
-    }
-
-    pub fn sess(&self) -> &Session {
-        &self.tcx.sess
-    }
-
-    pub fn errors_reported_since_creation(&self) -> bool {
-        self.tcx.sess.err_count() > self.err_count_on_creation
-    }
-
-    /// Produces warning on the given node, if the current point in the
-    /// function is unreachable, and there hasn't been another warning.
-    pub(super) fn warn_if_unreachable(&self, id: hir::HirId, span: Span, kind: &str) {
-        // FIXME: Combine these two 'if' expressions into one once
-        // let chains are implemented
-        if let Diverges::Always { span: orig_span, custom_note } = self.diverges.get() {
-            // If span arose from a desugaring of `if` or `while`, then it is the condition itself,
-            // which diverges, that we are about to lint on. This gives suboptimal diagnostics.
-            // Instead, stop here so that the `if`- or `while`-expression's block is linted instead.
-            if !span.is_desugaring(DesugaringKind::CondTemporary)
-                && !span.is_desugaring(DesugaringKind::Async)
-                && !orig_span.is_desugaring(DesugaringKind::Await)
-            {
-                self.diverges.set(Diverges::WarnedAlways);
-
-                debug!("warn_if_unreachable: id={:?} span={:?} kind={}", id, span, kind);
-
-                self.tcx().struct_span_lint_hir(lint::builtin::UNREACHABLE_CODE, id, span, |lint| {
-                    let msg = format!("unreachable {}", kind);
-                    lint.build(&msg)
-                        .span_label(span, &msg)
-                        .span_label(
-                            orig_span,
-                            custom_note
-                                .unwrap_or("any code following this expression is unreachable"),
-                        )
-                        .emit();
-                })
-            }
-        }
-    }
-
-    pub fn cause(&self, span: Span, code: ObligationCauseCode<'tcx>) -> ObligationCause<'tcx> {
-        ObligationCause::new(span, self.body_id, code)
-    }
-
-    pub fn misc(&self, span: Span) -> ObligationCause<'tcx> {
-        self.cause(span, ObligationCauseCode::MiscObligation)
-    }
-
-    /// Resolves type and const variables in `ty` if possible. Unlike the infcx
-    /// version (resolve_vars_if_possible), this version will
-    /// also select obligations if it seems useful, in an effort
-    /// to get more type information.
-    pub(super) fn resolve_vars_with_obligations(&self, mut ty: Ty<'tcx>) -> Ty<'tcx> {
-        debug!("resolve_vars_with_obligations(ty={:?})", ty);
-
-        // No Infer()? Nothing needs doing.
-        if !ty.has_infer_types_or_consts() {
-            debug!("resolve_vars_with_obligations: ty={:?}", ty);
-            return ty;
-        }
-
-        // If `ty` is a type variable, see whether we already know what it is.
-        ty = self.resolve_vars_if_possible(&ty);
-        if !ty.has_infer_types_or_consts() {
-            debug!("resolve_vars_with_obligations: ty={:?}", ty);
-            return ty;
-        }
-
-        // If not, try resolving pending obligations as much as
-        // possible. This can help substantially when there are
-        // indirect dependencies that don't seem worth tracking
-        // precisely.
-        self.select_obligations_where_possible(false, |_| {});
-        ty = self.resolve_vars_if_possible(&ty);
-
-        debug!("resolve_vars_with_obligations: ty={:?}", ty);
-        ty
-    }
-
-    pub(super) fn record_deferred_call_resolution(
-        &self,
-        closure_def_id: DefId,
-        r: DeferredCallResolution<'tcx>,
-    ) {
-        let mut deferred_call_resolutions = self.deferred_call_resolutions.borrow_mut();
-        deferred_call_resolutions.entry(closure_def_id).or_default().push(r);
-    }
-
-    pub(super) fn remove_deferred_call_resolutions(
-        &self,
-        closure_def_id: DefId,
-    ) -> Vec<DeferredCallResolution<'tcx>> {
-        let mut deferred_call_resolutions = self.deferred_call_resolutions.borrow_mut();
-        deferred_call_resolutions.remove(&closure_def_id).unwrap_or(vec![])
-    }
-
-    pub fn tag(&self) -> String {
-        format!("{:p}", self)
-    }
-
-    pub fn local_ty(&self, span: Span, nid: hir::HirId) -> LocalTy<'tcx> {
-        self.locals.borrow().get(&nid).cloned().unwrap_or_else(|| {
-            span_bug!(span, "no type for local variable {}", self.tcx.hir().node_to_string(nid))
-        })
-    }
-
-    #[inline]
-    pub fn write_ty(&self, id: hir::HirId, ty: Ty<'tcx>) {
-        debug!(
-            "write_ty({:?}, {:?}) in fcx {}",
-            id,
-            self.resolve_vars_if_possible(&ty),
-            self.tag()
-        );
-        self.typeck_results.borrow_mut().node_types_mut().insert(id, ty);
-
-        if ty.references_error() {
-            self.has_errors.set(true);
-            self.set_tainted_by_errors();
-        }
-    }
-
-    pub fn write_field_index(&self, hir_id: hir::HirId, index: usize) {
-        self.typeck_results.borrow_mut().field_indices_mut().insert(hir_id, index);
-    }
-
-    fn write_resolution(&self, hir_id: hir::HirId, r: Result<(DefKind, DefId), ErrorReported>) {
-        self.typeck_results.borrow_mut().type_dependent_defs_mut().insert(hir_id, r);
-    }
-
-    pub fn write_method_call(&self, hir_id: hir::HirId, method: MethodCallee<'tcx>) {
-        debug!("write_method_call(hir_id={:?}, method={:?})", hir_id, method);
-        self.write_resolution(hir_id, Ok((DefKind::AssocFn, method.def_id)));
-        self.write_substs(hir_id, method.substs);
-
-        // When the method is confirmed, the `method.substs` includes
-        // parameters from not just the method, but also the impl of
-        // the method -- in particular, the `Self` type will be fully
-        // resolved. However, those are not something that the "user
-        // specified" -- i.e., those types come from the inferred type
-        // of the receiver, not something the user wrote. So when we
-        // create the user-substs, we want to replace those earlier
-        // types with just the types that the user actually wrote --
-        // that is, those that appear on the *method itself*.
-        //
-        // As an example, if the user wrote something like
-        // `foo.bar::<u32>(...)` -- the `Self` type here will be the
-        // type of `foo` (possibly adjusted), but we don't want to
-        // include that. We want just the `[_, u32]` part.
-        if !method.substs.is_noop() {
-            let method_generics = self.tcx.generics_of(method.def_id);
-            if !method_generics.params.is_empty() {
-                let user_type_annotation = self.infcx.probe(|_| {
-                    let user_substs = UserSubsts {
-                        substs: InternalSubsts::for_item(self.tcx, method.def_id, |param, _| {
-                            let i = param.index as usize;
-                            if i < method_generics.parent_count {
-                                self.infcx.var_for_def(DUMMY_SP, param)
-                            } else {
-                                method.substs[i]
-                            }
-                        }),
-                        user_self_ty: None, // not relevant here
-                    };
-
-                    self.infcx.canonicalize_user_type_annotation(&UserType::TypeOf(
-                        method.def_id,
-                        user_substs,
-                    ))
-                });
-
-                debug!("write_method_call: user_type_annotation={:?}", user_type_annotation);
-                self.write_user_type_annotation(hir_id, user_type_annotation);
-            }
-        }
-    }
-
-    pub fn write_substs(&self, node_id: hir::HirId, substs: SubstsRef<'tcx>) {
-        if !substs.is_noop() {
-            debug!("write_substs({:?}, {:?}) in fcx {}", node_id, substs, self.tag());
-
-            self.typeck_results.borrow_mut().node_substs_mut().insert(node_id, substs);
-        }
-    }
-
-    /// Given the substs that we just converted from the HIR, try to
-    /// canonicalize them and store them as user-given substitutions
-    /// (i.e., substitutions that must be respected by the NLL check).
-    ///
-    /// This should be invoked **before any unifications have
-    /// occurred**, so that annotations like `Vec<_>` are preserved
-    /// properly.
-    pub fn write_user_type_annotation_from_substs(
-        &self,
-        hir_id: hir::HirId,
-        def_id: DefId,
-        substs: SubstsRef<'tcx>,
-        user_self_ty: Option<UserSelfTy<'tcx>>,
-    ) {
-        debug!(
-            "write_user_type_annotation_from_substs: hir_id={:?} def_id={:?} substs={:?} \
-             user_self_ty={:?} in fcx {}",
-            hir_id,
-            def_id,
-            substs,
-            user_self_ty,
-            self.tag(),
-        );
-
-        if Self::can_contain_user_lifetime_bounds((substs, user_self_ty)) {
-            let canonicalized = self.infcx.canonicalize_user_type_annotation(&UserType::TypeOf(
-                def_id,
-                UserSubsts { substs, user_self_ty },
-            ));
-            debug!("write_user_type_annotation_from_substs: canonicalized={:?}", canonicalized);
-            self.write_user_type_annotation(hir_id, canonicalized);
-        }
-    }
-
-    pub fn write_user_type_annotation(
-        &self,
-        hir_id: hir::HirId,
-        canonical_user_type_annotation: CanonicalUserType<'tcx>,
-    ) {
-        debug!(
-            "write_user_type_annotation: hir_id={:?} canonical_user_type_annotation={:?} tag={}",
-            hir_id,
-            canonical_user_type_annotation,
-            self.tag(),
-        );
-
-        if !canonical_user_type_annotation.is_identity() {
-            self.typeck_results
-                .borrow_mut()
-                .user_provided_types_mut()
-                .insert(hir_id, canonical_user_type_annotation);
-        } else {
-            debug!("write_user_type_annotation: skipping identity substs");
-        }
-    }
-
-    pub fn apply_adjustments(&self, expr: &hir::Expr<'_>, adj: Vec<Adjustment<'tcx>>) {
-        debug!("apply_adjustments(expr={:?}, adj={:?})", expr, adj);
-
-        if adj.is_empty() {
-            return;
-        }
-
-        let autoborrow_mut = adj.iter().any(|adj| {
-            matches!(adj, &Adjustment {
-                kind: Adjust::Borrow(AutoBorrow::Ref(_, AutoBorrowMutability::Mut { .. })),
-                ..
-            })
-        });
-
-        match self.typeck_results.borrow_mut().adjustments_mut().entry(expr.hir_id) {
-            Entry::Vacant(entry) => {
-                entry.insert(adj);
-            }
-            Entry::Occupied(mut entry) => {
-                debug!(" - composing on top of {:?}", entry.get());
-                match (&entry.get()[..], &adj[..]) {
-                    // Applying any adjustment on top of a NeverToAny
-                    // is a valid NeverToAny adjustment, because it can't
-                    // be reached.
-                    (&[Adjustment { kind: Adjust::NeverToAny, .. }], _) => return,
-                    (&[
-                        Adjustment { kind: Adjust::Deref(_), .. },
-                        Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(..)), .. },
-                    ], &[
-                        Adjustment { kind: Adjust::Deref(_), .. },
-                        .. // Any following adjustments are allowed.
-                    ]) => {
-                        // A reborrow has no effect before a dereference.
-                    }
-                    // FIXME: currently we never try to compose autoderefs
-                    // and ReifyFnPointer/UnsafeFnPointer, but we could.
-                    _ =>
-                        bug!("while adjusting {:?}, can't compose {:?} and {:?}",
-                             expr, entry.get(), adj)
-                };
-                *entry.get_mut() = adj;
-            }
-        }
-
-        // If there is an mutable auto-borrow, it is equivalent to `&mut <expr>`.
-        // In this case implicit use of `Deref` and `Index` within `<expr>` should
-        // instead be `DerefMut` and `IndexMut`, so fix those up.
-        if autoborrow_mut {
-            self.convert_place_derefs_to_mutable(expr);
-        }
-    }
-
-    /// Basically whenever we are converting from a type scheme into
-    /// the fn body space, we always want to normalize associated
-    /// types as well. This function combines the two.
-    fn instantiate_type_scheme<T>(&self, span: Span, substs: SubstsRef<'tcx>, value: &T) -> T
-    where
-        T: TypeFoldable<'tcx>,
-    {
-        let value = value.subst(self.tcx, substs);
-        let result = self.normalize_associated_types_in(span, &value);
-        debug!("instantiate_type_scheme(value={:?}, substs={:?}) = {:?}", value, substs, result);
-        result
-    }
-
-    /// As `instantiate_type_scheme`, but for the bounds found in a
-    /// generic type scheme.
-    fn instantiate_bounds(
-        &self,
-        span: Span,
-        def_id: DefId,
-        substs: SubstsRef<'tcx>,
-    ) -> (ty::InstantiatedPredicates<'tcx>, Vec<Span>) {
-        let bounds = self.tcx.predicates_of(def_id);
-        let spans: Vec<Span> = bounds.predicates.iter().map(|(_, span)| *span).collect();
-        let result = bounds.instantiate(self.tcx, substs);
-        let result = self.normalize_associated_types_in(span, &result);
-        debug!(
-            "instantiate_bounds(bounds={:?}, substs={:?}) = {:?}, {:?}",
-            bounds, substs, result, spans,
-        );
-        (result, spans)
-    }
-
-    /// Replaces the opaque types from the given value with type variables,
-    /// and records the `OpaqueTypeMap` for later use during writeback. See
-    /// `InferCtxt::instantiate_opaque_types` for more details.
-    pub(super) fn instantiate_opaque_types_from_value<T: TypeFoldable<'tcx>>(
-        &self,
-        parent_id: hir::HirId,
-        value: &T,
-        value_span: Span,
-    ) -> T {
-        let parent_def_id = self.tcx.hir().local_def_id(parent_id);
-        debug!(
-            "instantiate_opaque_types_from_value(parent_def_id={:?}, value={:?})",
-            parent_def_id, value
-        );
-
-        let (value, opaque_type_map) =
-            self.register_infer_ok_obligations(self.instantiate_opaque_types(
-                parent_def_id,
-                self.body_id,
-                self.param_env,
-                value,
-                value_span,
-            ));
-
-        let mut opaque_types = self.opaque_types.borrow_mut();
-        let mut opaque_types_vars = self.opaque_types_vars.borrow_mut();
-        for (ty, decl) in opaque_type_map {
-            let _ = opaque_types.insert(ty, decl);
-            let _ = opaque_types_vars.insert(decl.concrete_ty, decl.opaque_type);
-        }
-
-        value
-    }
-
-    pub(super) fn normalize_associated_types_in<T>(&self, span: Span, value: &T) -> T
-    where
-        T: TypeFoldable<'tcx>,
-    {
-        self.inh.normalize_associated_types_in(span, self.body_id, self.param_env, value)
-    }
-
-    pub(super) fn normalize_associated_types_in_as_infer_ok<T>(
-        &self,
-        span: Span,
-        value: &T,
-    ) -> InferOk<'tcx, T>
-    where
-        T: TypeFoldable<'tcx>,
-    {
-        self.inh.partially_normalize_associated_types_in(span, self.body_id, self.param_env, value)
-    }
-
-    pub fn require_type_meets(
-        &self,
-        ty: Ty<'tcx>,
-        span: Span,
-        code: traits::ObligationCauseCode<'tcx>,
-        def_id: DefId,
-    ) {
-        self.register_bound(ty, def_id, traits::ObligationCause::new(span, self.body_id, code));
-    }
-
-    pub fn require_type_is_sized(
-        &self,
-        ty: Ty<'tcx>,
-        span: Span,
-        code: traits::ObligationCauseCode<'tcx>,
-    ) {
-        if !ty.references_error() {
-            let lang_item = self.tcx.require_lang_item(LangItem::Sized, None);
-            self.require_type_meets(ty, span, code, lang_item);
-        }
-    }
-
-    pub fn require_type_is_sized_deferred(
-        &self,
-        ty: Ty<'tcx>,
-        span: Span,
-        code: traits::ObligationCauseCode<'tcx>,
-    ) {
-        if !ty.references_error() {
-            self.deferred_sized_obligations.borrow_mut().push((ty, span, code));
-        }
-    }
-
-    pub fn register_bound(
-        &self,
-        ty: Ty<'tcx>,
-        def_id: DefId,
-        cause: traits::ObligationCause<'tcx>,
-    ) {
-        if !ty.references_error() {
-            self.fulfillment_cx.borrow_mut().register_bound(
-                self,
-                self.param_env,
-                ty,
-                def_id,
-                cause,
-            );
-        }
-    }
-
-    pub fn to_ty(&self, ast_t: &hir::Ty<'_>) -> Ty<'tcx> {
-        let t = AstConv::ast_ty_to_ty(self, ast_t);
-        self.register_wf_obligation(t.into(), ast_t.span, traits::MiscObligation);
-        t
-    }
-
-    pub fn to_ty_saving_user_provided_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
-        let ty = self.to_ty(ast_ty);
-        debug!("to_ty_saving_user_provided_ty: ty={:?}", ty);
-
-        if Self::can_contain_user_lifetime_bounds(ty) {
-            let c_ty = self.infcx.canonicalize_response(&UserType::Ty(ty));
-            debug!("to_ty_saving_user_provided_ty: c_ty={:?}", c_ty);
-            self.typeck_results.borrow_mut().user_provided_types_mut().insert(ast_ty.hir_id, c_ty);
-        }
-
-        ty
-    }
-
-    pub fn to_const(&self, ast_c: &hir::AnonConst) -> &'tcx ty::Const<'tcx> {
-        let const_def_id = self.tcx.hir().local_def_id(ast_c.hir_id);
-        let c = ty::Const::from_anon_const(self.tcx, const_def_id);
-        self.register_wf_obligation(
-            c.into(),
-            self.tcx.hir().span(ast_c.hir_id),
-            ObligationCauseCode::MiscObligation,
-        );
-        c
-    }
-
-    pub fn const_arg_to_const(
-        &self,
-        ast_c: &hir::AnonConst,
-        param_def_id: DefId,
-    ) -> &'tcx ty::Const<'tcx> {
-        let const_def = ty::WithOptConstParam {
-            did: self.tcx.hir().local_def_id(ast_c.hir_id),
-            const_param_did: Some(param_def_id),
-        };
-        let c = ty::Const::from_opt_const_arg_anon_const(self.tcx, const_def);
-        self.register_wf_obligation(
-            c.into(),
-            self.tcx.hir().span(ast_c.hir_id),
-            ObligationCauseCode::MiscObligation,
-        );
-        c
-    }
-
-    // If the type given by the user has free regions, save it for later, since
-    // NLL would like to enforce those. Also pass in types that involve
-    // projections, since those can resolve to `'static` bounds (modulo #54940,
-    // which hopefully will be fixed by the time you see this comment, dear
-    // reader, although I have my doubts). Also pass in types with inference
-    // types, because they may be repeated. Other sorts of things are already
-    // sufficiently enforced with erased regions. =)
-    fn can_contain_user_lifetime_bounds<T>(t: T) -> bool
-    where
-        T: TypeFoldable<'tcx>,
-    {
-        t.has_free_regions() || t.has_projections() || t.has_infer_types()
-    }
-
-    pub fn node_ty(&self, id: hir::HirId) -> Ty<'tcx> {
-        match self.typeck_results.borrow().node_types().get(id) {
-            Some(&t) => t,
-            None if self.is_tainted_by_errors() => self.tcx.ty_error(),
-            None => {
-                bug!(
-                    "no type for node {}: {} in fcx {}",
-                    id,
-                    self.tcx.hir().node_to_string(id),
-                    self.tag()
-                );
-            }
-        }
-    }
-
-    /// Registers an obligation for checking later, during regionck, that `arg` is well-formed.
-    pub fn register_wf_obligation(
-        &self,
-        arg: subst::GenericArg<'tcx>,
-        span: Span,
-        code: traits::ObligationCauseCode<'tcx>,
-    ) {
-        // WF obligations never themselves fail, so no real need to give a detailed cause:
-        let cause = traits::ObligationCause::new(span, self.body_id, code);
-        self.register_predicate(traits::Obligation::new(
-            cause,
-            self.param_env,
-            ty::PredicateAtom::WellFormed(arg).to_predicate(self.tcx),
-        ));
-    }
-
-    /// Registers obligations that all `substs` are well-formed.
-    pub fn add_wf_bounds(&self, substs: SubstsRef<'tcx>, expr: &hir::Expr<'_>) {
-        for arg in substs.iter().filter(|arg| {
-            matches!(arg.unpack(), GenericArgKind::Type(..) | GenericArgKind::Const(..))
-        }) {
-            self.register_wf_obligation(arg, expr.span, traits::MiscObligation);
-        }
-    }
-
-    /// Given a fully substituted set of bounds (`generic_bounds`), and the values with which each
-    /// type/region parameter was instantiated (`substs`), creates and registers suitable
-    /// trait/region obligations.
-    ///
-    /// For example, if there is a function:
-    ///
-    /// ```
-    /// fn foo<'a,T:'a>(...)
-    /// ```
-    ///
-    /// and a reference:
-    ///
-    /// ```
-    /// let f = foo;
-    /// ```
-    ///
-    /// Then we will create a fresh region variable `'$0` and a fresh type variable `$1` for `'a`
-    /// and `T`. This routine will add a region obligation `$1:'$0` and register it locally.
-    pub fn add_obligations_for_parameters(
-        &self,
-        cause: traits::ObligationCause<'tcx>,
-        predicates: ty::InstantiatedPredicates<'tcx>,
-    ) {
-        assert!(!predicates.has_escaping_bound_vars());
-
-        debug!("add_obligations_for_parameters(predicates={:?})", predicates);
-
-        for obligation in traits::predicates_for_generics(cause, self.param_env, predicates) {
-            self.register_predicate(obligation);
-        }
-    }
-
-    // FIXME(arielb1): use this instead of field.ty everywhere
-    // Only for fields! Returns <none> for methods>
-    // Indifferent to privacy flags
-    pub fn field_ty(
-        &self,
-        span: Span,
-        field: &'tcx ty::FieldDef,
-        substs: SubstsRef<'tcx>,
-    ) -> Ty<'tcx> {
-        self.normalize_associated_types_in(span, &field.ty(self.tcx, substs))
-    }
-
-    pub(super) fn check_casts(&self) {
-        let mut deferred_cast_checks = self.deferred_cast_checks.borrow_mut();
-        for cast in deferred_cast_checks.drain(..) {
-            cast.check(self);
-        }
-    }
-
-    pub(super) fn resolve_generator_interiors(&self, def_id: DefId) {
-        let mut generators = self.deferred_generator_interiors.borrow_mut();
-        for (body_id, interior, kind) in generators.drain(..) {
-            self.select_obligations_where_possible(false, |_| {});
-            super::generator_interior::resolve_interior(self, def_id, body_id, interior, kind);
-        }
-    }
-
-    // Tries to apply a fallback to `ty` if it is an unsolved variable.
-    //
-    // - Unconstrained ints are replaced with `i32`.
-    //
-    // - Unconstrained floats are replaced with with `f64`.
-    //
-    // - Non-numerics get replaced with `!` when `#![feature(never_type_fallback)]`
-    //   is enabled. Otherwise, they are replaced with `()`.
-    //
-    // Fallback becomes very dubious if we have encountered type-checking errors.
-    // In that case, fallback to Error.
-    // The return value indicates whether fallback has occurred.
-    pub(super) fn fallback_if_possible(&self, ty: Ty<'tcx>, mode: FallbackMode) -> bool {
-        use rustc_middle::ty::error::UnconstrainedNumeric::Neither;
-        use rustc_middle::ty::error::UnconstrainedNumeric::{UnconstrainedFloat, UnconstrainedInt};
-
-        assert!(ty.is_ty_infer());
-        let fallback = match self.type_is_unconstrained_numeric(ty) {
-            _ if self.is_tainted_by_errors() => self.tcx().ty_error(),
-            UnconstrainedInt => self.tcx.types.i32,
-            UnconstrainedFloat => self.tcx.types.f64,
-            Neither if self.type_var_diverges(ty) => self.tcx.mk_diverging_default(),
-            Neither => {
-                // This type variable was created from the instantiation of an opaque
-                // type. The fact that we're attempting to perform fallback for it
-                // means that the function neither constrained it to a concrete
-                // type, nor to the opaque type itself.
-                //
-                // For example, in this code:
-                //
-                //```
-                // type MyType = impl Copy;
-                // fn defining_use() -> MyType { true }
-                // fn other_use() -> MyType { defining_use() }
-                // ```
-                //
-                // `defining_use` will constrain the instantiated inference
-                // variable to `bool`, while `other_use` will constrain
-                // the instantiated inference variable to `MyType`.
-                //
-                // When we process opaque types during writeback, we
-                // will handle cases like `other_use`, and not count
-                // them as defining usages
-                //
-                // However, we also need to handle cases like this:
-                //
-                // ```rust
-                // pub type Foo = impl Copy;
-                // fn produce() -> Option<Foo> {
-                //     None
-                //  }
-                //  ```
-                //
-                // In the above snippet, the inference variable created by
-                // instantiating `Option<Foo>` will be completely unconstrained.
-                // We treat this as a non-defining use by making the inference
-                // variable fall back to the opaque type itself.
-                if let FallbackMode::All = mode {
-                    if let Some(opaque_ty) = self.opaque_types_vars.borrow().get(ty) {
-                        debug!(
-                            "fallback_if_possible: falling back opaque type var {:?} to {:?}",
-                            ty, opaque_ty
-                        );
-                        *opaque_ty
-                    } else {
-                        return false;
-                    }
-                } else {
-                    return false;
-                }
-            }
-        };
-        debug!("fallback_if_possible: defaulting `{:?}` to `{:?}`", ty, fallback);
-        self.demand_eqtype(rustc_span::DUMMY_SP, ty, fallback);
-        true
-    }
-
-    pub(super) fn select_all_obligations_or_error(&self) {
-        debug!("select_all_obligations_or_error");
-        if let Err(errors) = self.fulfillment_cx.borrow_mut().select_all_or_error(&self) {
-            self.report_fulfillment_errors(&errors, self.inh.body_id, false);
-        }
-    }
-
-    /// Select as many obligations as we can at present.
-    pub(super) fn select_obligations_where_possible(
-        &self,
-        fallback_has_occurred: bool,
-        mutate_fullfillment_errors: impl Fn(&mut Vec<traits::FulfillmentError<'tcx>>),
-    ) {
-        let result = self.fulfillment_cx.borrow_mut().select_where_possible(self);
-        if let Err(mut errors) = result {
-            mutate_fullfillment_errors(&mut errors);
-            self.report_fulfillment_errors(&errors, self.inh.body_id, fallback_has_occurred);
-        }
-    }
-
-    /// For the overloaded place expressions (`*x`, `x[3]`), the trait
-    /// returns a type of `&T`, but the actual type we assign to the
-    /// *expression* is `T`. So this function just peels off the return
-    /// type by one layer to yield `T`.
-    pub(super) fn make_overloaded_place_return_type(
-        &self,
-        method: MethodCallee<'tcx>,
-    ) -> ty::TypeAndMut<'tcx> {
-        // extract method return type, which will be &T;
-        let ret_ty = method.sig.output();
-
-        // method returns &T, but the type as visible to user is T, so deref
-        ret_ty.builtin_deref(true).unwrap()
-    }
-
-    pub(super) fn check_method_argument_types(
-        &self,
-        sp: Span,
-        expr: &'tcx hir::Expr<'tcx>,
-        method: Result<MethodCallee<'tcx>, ()>,
-        args_no_rcvr: &'tcx [hir::Expr<'tcx>],
-        tuple_arguments: TupleArgumentsFlag,
-        expected: Expectation<'tcx>,
-    ) -> Ty<'tcx> {
-        let has_error = match method {
-            Ok(method) => method.substs.references_error() || method.sig.references_error(),
-            Err(_) => true,
-        };
-        if has_error {
-            let err_inputs = self.err_args(args_no_rcvr.len());
-
-            let err_inputs = match tuple_arguments {
-                DontTupleArguments => err_inputs,
-                TupleArguments => vec![self.tcx.intern_tup(&err_inputs[..])],
-            };
-
-            self.check_argument_types(
-                sp,
-                expr,
-                &err_inputs[..],
-                &[],
-                args_no_rcvr,
-                false,
-                tuple_arguments,
-                None,
-            );
-            return self.tcx.ty_error();
-        }
-
-        let method = method.unwrap();
-        // HACK(eddyb) ignore self in the definition (see above).
-        let expected_arg_tys = self.expected_inputs_for_expected_output(
-            sp,
-            expected,
-            method.sig.output(),
-            &method.sig.inputs()[1..],
-        );
-        self.check_argument_types(
-            sp,
-            expr,
-            &method.sig.inputs()[1..],
-            &expected_arg_tys[..],
-            args_no_rcvr,
-            method.sig.c_variadic,
-            tuple_arguments,
-            self.tcx.hir().span_if_local(method.def_id),
-        );
-        method.sig.output()
-    }
-
-    fn self_type_matches_expected_vid(
-        &self,
-        trait_ref: ty::PolyTraitRef<'tcx>,
-        expected_vid: ty::TyVid,
-    ) -> bool {
-        let self_ty = self.shallow_resolve(trait_ref.skip_binder().self_ty());
-        debug!(
-            "self_type_matches_expected_vid(trait_ref={:?}, self_ty={:?}, expected_vid={:?})",
-            trait_ref, self_ty, expected_vid
-        );
-        match *self_ty.kind() {
-            ty::Infer(ty::TyVar(found_vid)) => {
-                // FIXME: consider using `sub_root_var` here so we
-                // can see through subtyping.
-                let found_vid = self.root_var(found_vid);
-                debug!("self_type_matches_expected_vid - found_vid={:?}", found_vid);
-                expected_vid == found_vid
-            }
-            _ => false,
-        }
-    }
-
-    pub(super) fn obligations_for_self_ty<'b>(
-        &'b self,
-        self_ty: ty::TyVid,
-    ) -> impl Iterator<Item = (ty::PolyTraitRef<'tcx>, traits::PredicateObligation<'tcx>)>
-    + Captures<'tcx>
-    + 'b {
-        // FIXME: consider using `sub_root_var` here so we
-        // can see through subtyping.
-        let ty_var_root = self.root_var(self_ty);
-        debug!(
-            "obligations_for_self_ty: self_ty={:?} ty_var_root={:?} pending_obligations={:?}",
-            self_ty,
-            ty_var_root,
-            self.fulfillment_cx.borrow().pending_obligations()
-        );
-
-        self.fulfillment_cx
-            .borrow()
-            .pending_obligations()
-            .into_iter()
-            .filter_map(move |obligation| {
-                match obligation.predicate.skip_binders() {
-                    ty::PredicateAtom::Projection(data) => {
-                        Some((ty::Binder::bind(data).to_poly_trait_ref(self.tcx), obligation))
-                    }
-                    ty::PredicateAtom::Trait(data, _) => {
-                        Some((ty::Binder::bind(data).to_poly_trait_ref(), obligation))
-                    }
-                    ty::PredicateAtom::Subtype(..) => None,
-                    ty::PredicateAtom::RegionOutlives(..) => None,
-                    ty::PredicateAtom::TypeOutlives(..) => None,
-                    ty::PredicateAtom::WellFormed(..) => None,
-                    ty::PredicateAtom::ObjectSafe(..) => None,
-                    ty::PredicateAtom::ConstEvaluatable(..) => None,
-                    ty::PredicateAtom::ConstEquate(..) => None,
-                    // N.B., this predicate is created by breaking down a
-                    // `ClosureType: FnFoo()` predicate, where
-                    // `ClosureType` represents some `Closure`. It can't
-                    // possibly be referring to the current closure,
-                    // because we haven't produced the `Closure` for
-                    // this closure yet; this is exactly why the other
-                    // code is looking for a self type of a unresolved
-                    // inference variable.
-                    ty::PredicateAtom::ClosureKind(..) => None,
-                    ty::PredicateAtom::TypeWellFormedFromEnv(..) => None,
-                }
-            })
-            .filter(move |(tr, _)| self.self_type_matches_expected_vid(*tr, ty_var_root))
-    }
-
-    pub(super) fn type_var_is_sized(&self, self_ty: ty::TyVid) -> bool {
-        self.obligations_for_self_ty(self_ty)
-            .any(|(tr, _)| Some(tr.def_id()) == self.tcx.lang_items().sized_trait())
-    }
-
-    /// Generic function that factors out common logic from function calls,
-    /// method calls and overloaded operators.
-    pub(super) fn check_argument_types(
-        &self,
-        sp: Span,
-        expr: &'tcx hir::Expr<'tcx>,
-        fn_inputs: &[Ty<'tcx>],
-        expected_arg_tys: &[Ty<'tcx>],
-        args: &'tcx [hir::Expr<'tcx>],
-        c_variadic: bool,
-        tuple_arguments: TupleArgumentsFlag,
-        def_span: Option<Span>,
-    ) {
-        let tcx = self.tcx;
-        // Grab the argument types, supplying fresh type variables
-        // if the wrong number of arguments were supplied
-        let supplied_arg_count = if tuple_arguments == DontTupleArguments { args.len() } else { 1 };
-
-        // All the input types from the fn signature must outlive the call
-        // so as to validate implied bounds.
-        for (&fn_input_ty, arg_expr) in fn_inputs.iter().zip(args.iter()) {
-            self.register_wf_obligation(fn_input_ty.into(), arg_expr.span, traits::MiscObligation);
-        }
-
-        let expected_arg_count = fn_inputs.len();
-
-        let param_count_error = |expected_count: usize,
-                                 arg_count: usize,
-                                 error_code: &str,
-                                 c_variadic: bool,
-                                 sugg_unit: bool| {
-            let (span, start_span, args) = match &expr.kind {
-                hir::ExprKind::Call(hir::Expr { span, .. }, args) => (*span, *span, &args[..]),
-                hir::ExprKind::MethodCall(path_segment, span, args, _) => (
-                    *span,
-                    // `sp` doesn't point at the whole `foo.bar()`, only at `bar`.
-                    path_segment
-                        .args
-                        .and_then(|args| args.args.iter().last())
-                        // Account for `foo.bar::<T>()`.
-                        .map(|arg| {
-                            // Skip the closing `>`.
-                            tcx.sess
-                                .source_map()
-                                .next_point(tcx.sess.source_map().next_point(arg.span()))
-                        })
-                        .unwrap_or(*span),
-                    &args[1..], // Skip the receiver.
-                ),
-                k => span_bug!(sp, "checking argument types on a non-call: `{:?}`", k),
-            };
-            let arg_spans = if args.is_empty() {
-                // foo()
-                // ^^^-- supplied 0 arguments
-                // |
-                // expected 2 arguments
-                vec![tcx.sess.source_map().next_point(start_span).with_hi(sp.hi())]
-            } else {
-                // foo(1, 2, 3)
-                // ^^^ -  -  - supplied 3 arguments
-                // |
-                // expected 2 arguments
-                args.iter().map(|arg| arg.span).collect::<Vec<Span>>()
-            };
-
-            let mut err = tcx.sess.struct_span_err_with_code(
-                span,
-                &format!(
-                    "this function takes {}{} but {} {} supplied",
-                    if c_variadic { "at least " } else { "" },
-                    potentially_plural_count(expected_count, "argument"),
-                    potentially_plural_count(arg_count, "argument"),
-                    if arg_count == 1 { "was" } else { "were" }
-                ),
-                DiagnosticId::Error(error_code.to_owned()),
-            );
-            let label = format!("supplied {}", potentially_plural_count(arg_count, "argument"));
-            for (i, span) in arg_spans.into_iter().enumerate() {
-                err.span_label(
-                    span,
-                    if arg_count == 0 || i + 1 == arg_count { &label } else { "" },
-                );
-            }
-
-            if let Some(def_s) = def_span.map(|sp| tcx.sess.source_map().guess_head_span(sp)) {
-                err.span_label(def_s, "defined here");
-            }
-            if sugg_unit {
-                let sugg_span = tcx.sess.source_map().end_point(expr.span);
-                // remove closing `)` from the span
-                let sugg_span = sugg_span.shrink_to_lo();
-                err.span_suggestion(
-                    sugg_span,
-                    "expected the unit value `()`; create it with empty parentheses",
-                    String::from("()"),
-                    Applicability::MachineApplicable,
-                );
-            } else {
-                err.span_label(
-                    span,
-                    format!(
-                        "expected {}{}",
-                        if c_variadic { "at least " } else { "" },
-                        potentially_plural_count(expected_count, "argument")
-                    ),
-                );
-            }
-            err.emit();
-        };
-
-        let mut expected_arg_tys = expected_arg_tys.to_vec();
-
-        let formal_tys = if tuple_arguments == TupleArguments {
-            let tuple_type = self.structurally_resolved_type(sp, fn_inputs[0]);
-            match tuple_type.kind() {
-                ty::Tuple(arg_types) if arg_types.len() != args.len() => {
-                    param_count_error(arg_types.len(), args.len(), "E0057", false, false);
-                    expected_arg_tys = vec![];
-                    self.err_args(args.len())
-                }
-                ty::Tuple(arg_types) => {
-                    expected_arg_tys = match expected_arg_tys.get(0) {
-                        Some(&ty) => match ty.kind() {
-                            ty::Tuple(ref tys) => tys.iter().map(|k| k.expect_ty()).collect(),
-                            _ => vec![],
-                        },
-                        None => vec![],
-                    };
-                    arg_types.iter().map(|k| k.expect_ty()).collect()
-                }
-                _ => {
-                    struct_span_err!(
-                        tcx.sess,
-                        sp,
-                        E0059,
-                        "cannot use call notation; the first type parameter \
-                         for the function trait is neither a tuple nor unit"
-                    )
-                    .emit();
-                    expected_arg_tys = vec![];
-                    self.err_args(args.len())
-                }
-            }
-        } else if expected_arg_count == supplied_arg_count {
-            fn_inputs.to_vec()
-        } else if c_variadic {
-            if supplied_arg_count >= expected_arg_count {
-                fn_inputs.to_vec()
-            } else {
-                param_count_error(expected_arg_count, supplied_arg_count, "E0060", true, false);
-                expected_arg_tys = vec![];
-                self.err_args(supplied_arg_count)
-            }
-        } else {
-            // is the missing argument of type `()`?
-            let sugg_unit = if expected_arg_tys.len() == 1 && supplied_arg_count == 0 {
-                self.resolve_vars_if_possible(&expected_arg_tys[0]).is_unit()
-            } else if fn_inputs.len() == 1 && supplied_arg_count == 0 {
-                self.resolve_vars_if_possible(&fn_inputs[0]).is_unit()
-            } else {
-                false
-            };
-            param_count_error(expected_arg_count, supplied_arg_count, "E0061", false, sugg_unit);
-
-            expected_arg_tys = vec![];
-            self.err_args(supplied_arg_count)
-        };
-
-        debug!(
-            "check_argument_types: formal_tys={:?}",
-            formal_tys.iter().map(|t| self.ty_to_string(*t)).collect::<Vec<String>>()
-        );
-
-        // If there is no expectation, expect formal_tys.
-        let expected_arg_tys =
-            if !expected_arg_tys.is_empty() { expected_arg_tys } else { formal_tys.clone() };
-
-        let mut final_arg_types: Vec<(usize, Ty<'_>, Ty<'_>)> = vec![];
-
-        // Check the arguments.
-        // We do this in a pretty awful way: first we type-check any arguments
-        // that are not closures, then we type-check the closures. This is so
-        // that we have more information about the types of arguments when we
-        // type-check the functions. This isn't really the right way to do this.
-        for &check_closures in &[false, true] {
-            debug!("check_closures={}", check_closures);
-
-            // More awful hacks: before we check argument types, try to do
-            // an "opportunistic" trait resolution of any trait bounds on
-            // the call. This helps coercions.
-            if check_closures {
-                self.select_obligations_where_possible(false, |errors| {
-                    self.point_at_type_arg_instead_of_call_if_possible(errors, expr);
-                    self.point_at_arg_instead_of_call_if_possible(
-                        errors,
-                        &final_arg_types[..],
-                        sp,
-                        &args,
-                    );
-                })
-            }
-
-            // For C-variadic functions, we don't have a declared type for all of
-            // the arguments hence we only do our usual type checking with
-            // the arguments who's types we do know.
-            let t = if c_variadic {
-                expected_arg_count
-            } else if tuple_arguments == TupleArguments {
-                args.len()
-            } else {
-                supplied_arg_count
-            };
-            for (i, arg) in args.iter().take(t).enumerate() {
-                // Warn only for the first loop (the "no closures" one).
-                // Closure arguments themselves can't be diverging, but
-                // a previous argument can, e.g., `foo(panic!(), || {})`.
-                if !check_closures {
-                    self.warn_if_unreachable(arg.hir_id, arg.span, "expression");
-                }
-
-                let is_closure = match arg.kind {
-                    ExprKind::Closure(..) => true,
-                    _ => false,
-                };
-
-                if is_closure != check_closures {
-                    continue;
-                }
-
-                debug!("checking the argument");
-                let formal_ty = formal_tys[i];
-
-                // The special-cased logic below has three functions:
-                // 1. Provide as good of an expected type as possible.
-                let expected = Expectation::rvalue_hint(self, expected_arg_tys[i]);
-
-                let checked_ty = self.check_expr_with_expectation(&arg, expected);
-
-                // 2. Coerce to the most detailed type that could be coerced
-                //    to, which is `expected_ty` if `rvalue_hint` returns an
-                //    `ExpectHasType(expected_ty)`, or the `formal_ty` otherwise.
-                let coerce_ty = expected.only_has_type(self).unwrap_or(formal_ty);
-                // We're processing function arguments so we definitely want to use
-                // two-phase borrows.
-                self.demand_coerce(&arg, checked_ty, coerce_ty, None, AllowTwoPhase::Yes);
-                final_arg_types.push((i, checked_ty, coerce_ty));
-
-                // 3. Relate the expected type and the formal one,
-                //    if the expected type was used for the coercion.
-                self.demand_suptype(arg.span, formal_ty, coerce_ty);
-            }
-        }
-
-        // We also need to make sure we at least write the ty of the other
-        // arguments which we skipped above.
-        if c_variadic {
-            fn variadic_error<'tcx>(s: &Session, span: Span, t: Ty<'tcx>, cast_ty: &str) {
-                use crate::structured_errors::{StructuredDiagnostic, VariadicError};
-                VariadicError::new(s, span, t, cast_ty).diagnostic().emit();
-            }
-
-            for arg in args.iter().skip(expected_arg_count) {
-                let arg_ty = self.check_expr(&arg);
-
-                // There are a few types which get autopromoted when passed via varargs
-                // in C but we just error out instead and require explicit casts.
-                let arg_ty = self.structurally_resolved_type(arg.span, arg_ty);
-                match arg_ty.kind() {
-                    ty::Float(ast::FloatTy::F32) => {
-                        variadic_error(tcx.sess, arg.span, arg_ty, "c_double");
-                    }
-                    ty::Int(ast::IntTy::I8 | ast::IntTy::I16) | ty::Bool => {
-                        variadic_error(tcx.sess, arg.span, arg_ty, "c_int");
-                    }
-                    ty::Uint(ast::UintTy::U8 | ast::UintTy::U16) => {
-                        variadic_error(tcx.sess, arg.span, arg_ty, "c_uint");
-                    }
-                    ty::FnDef(..) => {
-                        let ptr_ty = self.tcx.mk_fn_ptr(arg_ty.fn_sig(self.tcx));
-                        let ptr_ty = self.resolve_vars_if_possible(&ptr_ty);
-                        variadic_error(tcx.sess, arg.span, arg_ty, &ptr_ty.to_string());
-                    }
-                    _ => {}
-                }
-            }
-        }
-    }
-
-    pub(super) fn err_args(&self, len: usize) -> Vec<Ty<'tcx>> {
-        vec![self.tcx.ty_error(); len]
-    }
-
-    /// Given a vec of evaluated `FulfillmentError`s and an `fn` call argument expressions, we walk
-    /// the checked and coerced types for each argument to see if any of the `FulfillmentError`s
-    /// reference a type argument. The reason to walk also the checked type is that the coerced type
-    /// can be not easily comparable with predicate type (because of coercion). If the types match
-    /// for either checked or coerced type, and there's only *one* argument that does, we point at
-    /// the corresponding argument's expression span instead of the `fn` call path span.
-    fn point_at_arg_instead_of_call_if_possible(
-        &self,
-        errors: &mut Vec<traits::FulfillmentError<'tcx>>,
-        final_arg_types: &[(usize, Ty<'tcx>, Ty<'tcx>)],
-        call_sp: Span,
-        args: &'tcx [hir::Expr<'tcx>],
-    ) {
-        // We *do not* do this for desugared call spans to keep good diagnostics when involving
-        // the `?` operator.
-        if call_sp.desugaring_kind().is_some() {
-            return;
-        }
-
-        for error in errors {
-            // Only if the cause is somewhere inside the expression we want try to point at arg.
-            // Otherwise, it means that the cause is somewhere else and we should not change
-            // anything because we can break the correct span.
-            if !call_sp.contains(error.obligation.cause.span) {
-                continue;
-            }
-
-            if let ty::PredicateAtom::Trait(predicate, _) =
-                error.obligation.predicate.skip_binders()
-            {
-                // Collect the argument position for all arguments that could have caused this
-                // `FulfillmentError`.
-                let mut referenced_in = final_arg_types
-                    .iter()
-                    .map(|&(i, checked_ty, _)| (i, checked_ty))
-                    .chain(final_arg_types.iter().map(|&(i, _, coerced_ty)| (i, coerced_ty)))
-                    .flat_map(|(i, ty)| {
-                        let ty = self.resolve_vars_if_possible(&ty);
-                        // We walk the argument type because the argument's type could have
-                        // been `Option<T>`, but the `FulfillmentError` references `T`.
-                        if ty.walk().any(|arg| arg == predicate.self_ty().into()) {
-                            Some(i)
-                        } else {
-                            None
-                        }
-                    })
-                    .collect::<Vec<usize>>();
-
-                // Both checked and coerced types could have matched, thus we need to remove
-                // duplicates.
-
-                // We sort primitive type usize here and can use unstable sort
-                referenced_in.sort_unstable();
-                referenced_in.dedup();
-
-                if let (Some(ref_in), None) = (referenced_in.pop(), referenced_in.pop()) {
-                    // We make sure that only *one* argument matches the obligation failure
-                    // and we assign the obligation's span to its expression's.
-                    error.obligation.cause.make_mut().span = args[ref_in].span;
-                    error.points_at_arg_span = true;
-                }
-            }
-        }
-    }
-
-    /// Given a vec of evaluated `FulfillmentError`s and an `fn` call expression, we walk the
-    /// `PathSegment`s and resolve their type parameters to see if any of the `FulfillmentError`s
-    /// were caused by them. If they were, we point at the corresponding type argument's span
-    /// instead of the `fn` call path span.
-    fn point_at_type_arg_instead_of_call_if_possible(
-        &self,
-        errors: &mut Vec<traits::FulfillmentError<'tcx>>,
-        call_expr: &'tcx hir::Expr<'tcx>,
-    ) {
-        if let hir::ExprKind::Call(path, _) = &call_expr.kind {
-            if let hir::ExprKind::Path(qpath) = &path.kind {
-                if let hir::QPath::Resolved(_, path) = &qpath {
-                    for error in errors {
-                        if let ty::PredicateAtom::Trait(predicate, _) =
-                            error.obligation.predicate.skip_binders()
-                        {
-                            // If any of the type arguments in this path segment caused the
-                            // `FullfillmentError`, point at its span (#61860).
-                            for arg in path
-                                .segments
-                                .iter()
-                                .filter_map(|seg| seg.args.as_ref())
-                                .flat_map(|a| a.args.iter())
-                            {
-                                if let hir::GenericArg::Type(hir_ty) = &arg {
-                                    if let hir::TyKind::Path(hir::QPath::TypeRelative(..)) =
-                                        &hir_ty.kind
-                                    {
-                                        // Avoid ICE with associated types. As this is best
-                                        // effort only, it's ok to ignore the case. It
-                                        // would trigger in `is_send::<T::AssocType>();`
-                                        // from `typeck-default-trait-impl-assoc-type.rs`.
-                                    } else {
-                                        let ty = AstConv::ast_ty_to_ty(self, hir_ty);
-                                        let ty = self.resolve_vars_if_possible(&ty);
-                                        if ty == predicate.self_ty() {
-                                            error.obligation.cause.make_mut().span = hir_ty.span;
-                                        }
-                                    }
-                                }
-                            }
-                        }
-                    }
-                }
-            }
-        }
-    }
-
-    // AST fragment checking
-    pub(super) fn check_lit(&self, lit: &hir::Lit, expected: Expectation<'tcx>) -> Ty<'tcx> {
-        let tcx = self.tcx;
-
-        match lit.node {
-            ast::LitKind::Str(..) => tcx.mk_static_str(),
-            ast::LitKind::ByteStr(ref v) => {
-                tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_array(tcx.types.u8, v.len() as u64))
-            }
-            ast::LitKind::Byte(_) => tcx.types.u8,
-            ast::LitKind::Char(_) => tcx.types.char,
-            ast::LitKind::Int(_, ast::LitIntType::Signed(t)) => tcx.mk_mach_int(t),
-            ast::LitKind::Int(_, ast::LitIntType::Unsigned(t)) => tcx.mk_mach_uint(t),
-            ast::LitKind::Int(_, ast::LitIntType::Unsuffixed) => {
-                let opt_ty = expected.to_option(self).and_then(|ty| match ty.kind() {
-                    ty::Int(_) | ty::Uint(_) => Some(ty),
-                    ty::Char => Some(tcx.types.u8),
-                    ty::RawPtr(..) => Some(tcx.types.usize),
-                    ty::FnDef(..) | ty::FnPtr(_) => Some(tcx.types.usize),
-                    _ => None,
-                });
-                opt_ty.unwrap_or_else(|| self.next_int_var())
-            }
-            ast::LitKind::Float(_, ast::LitFloatType::Suffixed(t)) => tcx.mk_mach_float(t),
-            ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) => {
-                let opt_ty = expected.to_option(self).and_then(|ty| match ty.kind() {
-                    ty::Float(_) => Some(ty),
-                    _ => None,
-                });
-                opt_ty.unwrap_or_else(|| self.next_float_var())
-            }
-            ast::LitKind::Bool(_) => tcx.types.bool,
-            ast::LitKind::Err(_) => tcx.ty_error(),
-        }
-    }
-
-    /// Unifies the output type with the expected type early, for more coercions
-    /// and forward type information on the input expressions.
-    pub(super) fn expected_inputs_for_expected_output(
-        &self,
-        call_span: Span,
-        expected_ret: Expectation<'tcx>,
-        formal_ret: Ty<'tcx>,
-        formal_args: &[Ty<'tcx>],
-    ) -> Vec<Ty<'tcx>> {
-        let formal_ret = self.resolve_vars_with_obligations(formal_ret);
-        let ret_ty = match expected_ret.only_has_type(self) {
-            Some(ret) => ret,
-            None => return Vec::new(),
-        };
-        let expect_args = self
-            .fudge_inference_if_ok(|| {
-                // Attempt to apply a subtyping relationship between the formal
-                // return type (likely containing type variables if the function
-                // is polymorphic) and the expected return type.
-                // No argument expectations are produced if unification fails.
-                let origin = self.misc(call_span);
-                let ures = self.at(&origin, self.param_env).sup(ret_ty, &formal_ret);
-
-                // FIXME(#27336) can't use ? here, Try::from_error doesn't default
-                // to identity so the resulting type is not constrained.
-                match ures {
-                    Ok(ok) => {
-                        // Process any obligations locally as much as
-                        // we can.  We don't care if some things turn
-                        // out unconstrained or ambiguous, as we're
-                        // just trying to get hints here.
-                        self.save_and_restore_in_snapshot_flag(|_| {
-                            let mut fulfill = TraitEngine::new(self.tcx);
-                            for obligation in ok.obligations {
-                                fulfill.register_predicate_obligation(self, obligation);
-                            }
-                            fulfill.select_where_possible(self)
-                        })
-                        .map_err(|_| ())?;
-                    }
-                    Err(_) => return Err(()),
-                }
-
-                // Record all the argument types, with the substitutions
-                // produced from the above subtyping unification.
-                Ok(formal_args.iter().map(|ty| self.resolve_vars_if_possible(ty)).collect())
-            })
-            .unwrap_or_default();
-        debug!(
-            "expected_inputs_for_expected_output(formal={:?} -> {:?}, expected={:?} -> {:?})",
-            formal_args, formal_ret, expect_args, expected_ret
-        );
-        expect_args
-    }
-
-    pub fn check_struct_path(
-        &self,
-        qpath: &QPath<'_>,
-        hir_id: hir::HirId,
-    ) -> Option<(&'tcx ty::VariantDef, Ty<'tcx>)> {
-        let path_span = qpath.qself_span();
-        let (def, ty) = self.finish_resolving_struct_path(qpath, path_span, hir_id);
-        let variant = match def {
-            Res::Err => {
-                self.set_tainted_by_errors();
-                return None;
-            }
-            Res::Def(DefKind::Variant, _) => match ty.kind() {
-                ty::Adt(adt, substs) => Some((adt.variant_of_res(def), adt.did, substs)),
-                _ => bug!("unexpected type: {:?}", ty),
-            },
-            Res::Def(DefKind::Struct | DefKind::Union | DefKind::TyAlias | DefKind::AssocTy, _)
-            | Res::SelfTy(..) => match ty.kind() {
-                ty::Adt(adt, substs) if !adt.is_enum() => {
-                    Some((adt.non_enum_variant(), adt.did, substs))
-                }
-                _ => None,
-            },
-            _ => bug!("unexpected definition: {:?}", def),
-        };
-
-        if let Some((variant, did, substs)) = variant {
-            debug!("check_struct_path: did={:?} substs={:?}", did, substs);
-            self.write_user_type_annotation_from_substs(hir_id, did, substs, None);
-
-            // Check bounds on type arguments used in the path.
-            let (bounds, _) = self.instantiate_bounds(path_span, did, substs);
-            let cause =
-                traits::ObligationCause::new(path_span, self.body_id, traits::ItemObligation(did));
-            self.add_obligations_for_parameters(cause, bounds);
-
-            Some((variant, ty))
-        } else {
-            struct_span_err!(
-                self.tcx.sess,
-                path_span,
-                E0071,
-                "expected struct, variant or union type, found {}",
-                ty.sort_string(self.tcx)
-            )
-            .span_label(path_span, "not a struct")
-            .emit();
-            None
-        }
-    }
-
-    // Finish resolving a path in a struct expression or pattern `S::A { .. }` if necessary.
-    // The newly resolved definition is written into `type_dependent_defs`.
-    fn finish_resolving_struct_path(
-        &self,
-        qpath: &QPath<'_>,
-        path_span: Span,
-        hir_id: hir::HirId,
-    ) -> (Res, Ty<'tcx>) {
-        match *qpath {
-            QPath::Resolved(ref maybe_qself, ref path) => {
-                let self_ty = maybe_qself.as_ref().map(|qself| self.to_ty(qself));
-                let ty = AstConv::res_to_ty(self, self_ty, path, true);
-                (path.res, ty)
-            }
-            QPath::TypeRelative(ref qself, ref segment) => {
-                let ty = self.to_ty(qself);
-
-                let res = if let hir::TyKind::Path(QPath::Resolved(_, ref path)) = qself.kind {
-                    path.res
-                } else {
-                    Res::Err
-                };
-                let result =
-                    AstConv::associated_path_to_ty(self, hir_id, path_span, ty, res, segment, true);
-                let ty = result.map(|(ty, _, _)| ty).unwrap_or_else(|_| self.tcx().ty_error());
-                let result = result.map(|(_, kind, def_id)| (kind, def_id));
-
-                // Write back the new resolution.
-                self.write_resolution(hir_id, result);
-
-                (result.map(|(kind, def_id)| Res::Def(kind, def_id)).unwrap_or(Res::Err), ty)
-            }
-            QPath::LangItem(lang_item, span) => {
-                self.resolve_lang_item_path(lang_item, span, hir_id)
-            }
-        }
-    }
-
-    pub(super) fn resolve_lang_item_path(
-        &self,
-        lang_item: hir::LangItem,
-        span: Span,
-        hir_id: hir::HirId,
-    ) -> (Res, Ty<'tcx>) {
-        let def_id = self.tcx.require_lang_item(lang_item, Some(span));
-        let def_kind = self.tcx.def_kind(def_id);
-
-        let item_ty = if let DefKind::Variant = def_kind {
-            self.tcx.type_of(self.tcx.parent(def_id).expect("variant w/out parent"))
-        } else {
-            self.tcx.type_of(def_id)
-        };
-        let substs = self.infcx.fresh_substs_for_item(span, def_id);
-        let ty = item_ty.subst(self.tcx, substs);
-
-        self.write_resolution(hir_id, Ok((def_kind, def_id)));
-        self.add_required_obligations(span, def_id, &substs);
-        (Res::Def(def_kind, def_id), ty)
-    }
-
-    /// Resolves an associated value path into a base type and associated constant, or method
-    /// resolution. The newly resolved definition is written into `type_dependent_defs`.
-    pub fn resolve_ty_and_res_ufcs<'b>(
-        &self,
-        qpath: &'b QPath<'b>,
-        hir_id: hir::HirId,
-        span: Span,
-    ) -> (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]) {
-        debug!("resolve_ty_and_res_ufcs: qpath={:?} hir_id={:?} span={:?}", qpath, hir_id, span);
-        let (ty, qself, item_segment) = match *qpath {
-            QPath::Resolved(ref opt_qself, ref path) => {
-                return (
-                    path.res,
-                    opt_qself.as_ref().map(|qself| self.to_ty(qself)),
-                    &path.segments[..],
-                );
-            }
-            QPath::TypeRelative(ref qself, ref segment) => (self.to_ty(qself), qself, segment),
-            QPath::LangItem(..) => bug!("`resolve_ty_and_res_ufcs` called on `LangItem`"),
-        };
-        if let Some(&cached_result) = self.typeck_results.borrow().type_dependent_defs().get(hir_id)
-        {
-            // Return directly on cache hit. This is useful to avoid doubly reporting
-            // errors with default match binding modes. See #44614.
-            let def =
-                cached_result.map(|(kind, def_id)| Res::Def(kind, def_id)).unwrap_or(Res::Err);
-            return (def, Some(ty), slice::from_ref(&**item_segment));
-        }
-        let item_name = item_segment.ident;
-        let result = self.resolve_ufcs(span, item_name, ty, hir_id).or_else(|error| {
-            let result = match error {
-                method::MethodError::PrivateMatch(kind, def_id, _) => Ok((kind, def_id)),
-                _ => Err(ErrorReported),
-            };
-            if item_name.name != kw::Invalid {
-                if let Some(mut e) = self.report_method_error(
-                    span,
-                    ty,
-                    item_name,
-                    SelfSource::QPath(qself),
-                    error,
-                    None,
-                ) {
-                    e.emit();
-                }
-            }
-            result
-        });
-
-        // Write back the new resolution.
-        self.write_resolution(hir_id, result);
-        (
-            result.map(|(kind, def_id)| Res::Def(kind, def_id)).unwrap_or(Res::Err),
-            Some(ty),
-            slice::from_ref(&**item_segment),
-        )
-    }
-
-    pub fn check_decl_initializer(
-        &self,
-        local: &'tcx hir::Local<'tcx>,
-        init: &'tcx hir::Expr<'tcx>,
-    ) -> Ty<'tcx> {
-        // FIXME(tschottdorf): `contains_explicit_ref_binding()` must be removed
-        // for #42640 (default match binding modes).
-        //
-        // See #44848.
-        let ref_bindings = local.pat.contains_explicit_ref_binding();
-
-        let local_ty = self.local_ty(init.span, local.hir_id).revealed_ty;
-        if let Some(m) = ref_bindings {
-            // Somewhat subtle: if we have a `ref` binding in the pattern,
-            // we want to avoid introducing coercions for the RHS. This is
-            // both because it helps preserve sanity and, in the case of
-            // ref mut, for soundness (issue #23116). In particular, in
-            // the latter case, we need to be clear that the type of the
-            // referent for the reference that results is *equal to* the
-            // type of the place it is referencing, and not some
-            // supertype thereof.
-            let init_ty = self.check_expr_with_needs(init, Needs::maybe_mut_place(m));
-            self.demand_eqtype(init.span, local_ty, init_ty);
-            init_ty
-        } else {
-            self.check_expr_coercable_to_type(init, local_ty, None)
-        }
-    }
-
-    /// Type check a `let` statement.
-    pub fn check_decl_local(&self, local: &'tcx hir::Local<'tcx>) {
-        // Determine and write the type which we'll check the pattern against.
-        let ty = self.local_ty(local.span, local.hir_id).decl_ty;
-        self.write_ty(local.hir_id, ty);
-
-        // Type check the initializer.
-        if let Some(ref init) = local.init {
-            let init_ty = self.check_decl_initializer(local, &init);
-            self.overwrite_local_ty_if_err(local, ty, init_ty);
-        }
-
-        // Does the expected pattern type originate from an expression and what is the span?
-        let (origin_expr, ty_span) = match (local.ty, local.init) {
-            (Some(ty), _) => (false, Some(ty.span)), // Bias towards the explicit user type.
-            (_, Some(init)) => (true, Some(init.span)), // No explicit type; so use the scrutinee.
-            _ => (false, None), // We have `let $pat;`, so the expected type is unconstrained.
-        };
-
-        // Type check the pattern. Override if necessary to avoid knock-on errors.
-        self.check_pat_top(&local.pat, ty, ty_span, origin_expr);
-        let pat_ty = self.node_ty(local.pat.hir_id);
-        self.overwrite_local_ty_if_err(local, ty, pat_ty);
-    }
-
-    fn overwrite_local_ty_if_err(
-        &self,
-        local: &'tcx hir::Local<'tcx>,
-        decl_ty: Ty<'tcx>,
-        ty: Ty<'tcx>,
-    ) {
-        if ty.references_error() {
-            // Override the types everywhere with `err()` to avoid knock on errors.
-            self.write_ty(local.hir_id, ty);
-            self.write_ty(local.pat.hir_id, ty);
-            let local_ty = LocalTy { decl_ty, revealed_ty: ty };
-            self.locals.borrow_mut().insert(local.hir_id, local_ty);
-            self.locals.borrow_mut().insert(local.pat.hir_id, local_ty);
-        }
-    }
-
-    pub(super) fn suggest_semicolon_at_end(&self, span: Span, err: &mut DiagnosticBuilder<'_>) {
-        err.span_suggestion_short(
-            span.shrink_to_hi(),
-            "consider using a semicolon here",
-            ";".to_string(),
-            Applicability::MachineApplicable,
-        );
-    }
-
-    pub fn check_stmt(&self, stmt: &'tcx hir::Stmt<'tcx>) {
-        // Don't do all the complex logic below for `DeclItem`.
-        match stmt.kind {
-            hir::StmtKind::Item(..) => return,
-            hir::StmtKind::Local(..) | hir::StmtKind::Expr(..) | hir::StmtKind::Semi(..) => {}
-        }
-
-        self.warn_if_unreachable(stmt.hir_id, stmt.span, "statement");
-
-        // Hide the outer diverging and `has_errors` flags.
-        let old_diverges = self.diverges.replace(Diverges::Maybe);
-        let old_has_errors = self.has_errors.replace(false);
-
-        match stmt.kind {
-            hir::StmtKind::Local(ref l) => {
-                self.check_decl_local(&l);
-            }
-            // Ignore for now.
-            hir::StmtKind::Item(_) => {}
-            hir::StmtKind::Expr(ref expr) => {
-                // Check with expected type of `()`.
-                self.check_expr_has_type_or_error(&expr, self.tcx.mk_unit(), |err| {
-                    self.suggest_semicolon_at_end(expr.span, err);
-                });
-            }
-            hir::StmtKind::Semi(ref expr) => {
-                self.check_expr(&expr);
-            }
-        }
-
-        // Combine the diverging and `has_error` flags.
-        self.diverges.set(self.diverges.get() | old_diverges);
-        self.has_errors.set(self.has_errors.get() | old_has_errors);
-    }
-
-    pub fn check_block_no_value(&self, blk: &'tcx hir::Block<'tcx>) {
-        let unit = self.tcx.mk_unit();
-        let ty = self.check_block_with_expected(blk, ExpectHasType(unit));
-
-        // if the block produces a `!` value, that can always be
-        // (effectively) coerced to unit.
-        if !ty.is_never() {
-            self.demand_suptype(blk.span, unit, ty);
-        }
-    }
-
-    /// If `expr` is a `match` expression that has only one non-`!` arm, use that arm's tail
-    /// expression's `Span`, otherwise return `expr.span`. This is done to give better errors
-    /// when given code like the following:
-    /// ```text
-    /// if false { return 0i32; } else { 1u32 }
-    /// //                               ^^^^ point at this instead of the whole `if` expression
-    /// ```
-    fn get_expr_coercion_span(&self, expr: &hir::Expr<'_>) -> rustc_span::Span {
-        if let hir::ExprKind::Match(_, arms, _) = &expr.kind {
-            let arm_spans: Vec<Span> = arms
-                .iter()
-                .filter_map(|arm| {
-                    self.in_progress_typeck_results
-                        .and_then(|typeck_results| {
-                            typeck_results.borrow().node_type_opt(arm.body.hir_id)
-                        })
-                        .and_then(|arm_ty| {
-                            if arm_ty.is_never() {
-                                None
-                            } else {
-                                Some(match &arm.body.kind {
-                                    // Point at the tail expression when possible.
-                                    hir::ExprKind::Block(block, _) => {
-                                        block.expr.as_ref().map(|e| e.span).unwrap_or(block.span)
-                                    }
-                                    _ => arm.body.span,
-                                })
-                            }
-                        })
-                })
-                .collect();
-            if arm_spans.len() == 1 {
-                return arm_spans[0];
-            }
-        }
-        expr.span
-    }
-
-    pub(super) fn check_block_with_expected(
-        &self,
-        blk: &'tcx hir::Block<'tcx>,
-        expected: Expectation<'tcx>,
-    ) -> Ty<'tcx> {
-        let prev = {
-            let mut fcx_ps = self.ps.borrow_mut();
-            let unsafety_state = fcx_ps.recurse(blk);
-            replace(&mut *fcx_ps, unsafety_state)
-        };
-
-        // In some cases, blocks have just one exit, but other blocks
-        // can be targeted by multiple breaks. This can happen both
-        // with labeled blocks as well as when we desugar
-        // a `try { ... }` expression.
-        //
-        // Example 1:
-        //
-        //    'a: { if true { break 'a Err(()); } Ok(()) }
-        //
-        // Here we would wind up with two coercions, one from
-        // `Err(())` and the other from the tail expression
-        // `Ok(())`. If the tail expression is omitted, that's a
-        // "forced unit" -- unless the block diverges, in which
-        // case we can ignore the tail expression (e.g., `'a: {
-        // break 'a 22; }` would not force the type of the block
-        // to be `()`).
-        let tail_expr = blk.expr.as_ref();
-        let coerce_to_ty = expected.coercion_target_type(self, blk.span);
-        let coerce = if blk.targeted_by_break {
-            CoerceMany::new(coerce_to_ty)
-        } else {
-            let tail_expr: &[&hir::Expr<'_>] = match tail_expr {
-                Some(e) => slice::from_ref(e),
-                None => &[],
-            };
-            CoerceMany::with_coercion_sites(coerce_to_ty, tail_expr)
-        };
-
-        let prev_diverges = self.diverges.get();
-        let ctxt = BreakableCtxt { coerce: Some(coerce), may_break: false };
-
-        let (ctxt, ()) = self.with_breakable_ctxt(blk.hir_id, ctxt, || {
-            for s in blk.stmts {
-                self.check_stmt(s);
-            }
-
-            // check the tail expression **without** holding the
-            // `enclosing_breakables` lock below.
-            let tail_expr_ty = tail_expr.map(|t| self.check_expr_with_expectation(t, expected));
-
-            let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
-            let ctxt = enclosing_breakables.find_breakable(blk.hir_id);
-            let coerce = ctxt.coerce.as_mut().unwrap();
-            if let Some(tail_expr_ty) = tail_expr_ty {
-                let tail_expr = tail_expr.unwrap();
-                let span = self.get_expr_coercion_span(tail_expr);
-                let cause = self.cause(span, ObligationCauseCode::BlockTailExpression(blk.hir_id));
-                coerce.coerce(self, &cause, tail_expr, tail_expr_ty);
-            } else {
-                // Subtle: if there is no explicit tail expression,
-                // that is typically equivalent to a tail expression
-                // of `()` -- except if the block diverges. In that
-                // case, there is no value supplied from the tail
-                // expression (assuming there are no other breaks,
-                // this implies that the type of the block will be
-                // `!`).
-                //
-                // #41425 -- label the implicit `()` as being the
-                // "found type" here, rather than the "expected type".
-                if !self.diverges.get().is_always() {
-                    // #50009 -- Do not point at the entire fn block span, point at the return type
-                    // span, as it is the cause of the requirement, and
-                    // `consider_hint_about_removing_semicolon` will point at the last expression
-                    // if it were a relevant part of the error. This improves usability in editors
-                    // that highlight errors inline.
-                    let mut sp = blk.span;
-                    let mut fn_span = None;
-                    if let Some((decl, ident)) = self.get_parent_fn_decl(blk.hir_id) {
-                        let ret_sp = decl.output.span();
-                        if let Some(block_sp) = self.parent_item_span(blk.hir_id) {
-                            // HACK: on some cases (`ui/liveness/liveness-issue-2163.rs`) the
-                            // output would otherwise be incorrect and even misleading. Make sure
-                            // the span we're aiming at correspond to a `fn` body.
-                            if block_sp == blk.span {
-                                sp = ret_sp;
-                                fn_span = Some(ident.span);
-                            }
-                        }
-                    }
-                    coerce.coerce_forced_unit(
-                        self,
-                        &self.misc(sp),
-                        &mut |err| {
-                            if let Some(expected_ty) = expected.only_has_type(self) {
-                                self.consider_hint_about_removing_semicolon(blk, expected_ty, err);
-                            }
-                            if let Some(fn_span) = fn_span {
-                                err.span_label(
-                                    fn_span,
-                                    "implicitly returns `()` as its body has no tail or `return` \
-                                     expression",
-                                );
-                            }
-                        },
-                        false,
-                    );
-                }
-            }
-        });
-
-        if ctxt.may_break {
-            // If we can break from the block, then the block's exit is always reachable
-            // (... as long as the entry is reachable) - regardless of the tail of the block.
-            self.diverges.set(prev_diverges);
-        }
-
-        let mut ty = ctxt.coerce.unwrap().complete(self);
-
-        if self.has_errors.get() || ty.references_error() {
-            ty = self.tcx.ty_error()
-        }
-
-        self.write_ty(blk.hir_id, ty);
-
-        *self.ps.borrow_mut() = prev;
-        ty
-    }
-
-    fn parent_item_span(&self, id: hir::HirId) -> Option<Span> {
-        let node = self.tcx.hir().get(self.tcx.hir().get_parent_item(id));
-        match node {
-            Node::Item(&hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. })
-            | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(_, body_id), .. }) => {
-                let body = self.tcx.hir().body(body_id);
-                if let ExprKind::Block(block, _) = &body.value.kind {
-                    return Some(block.span);
-                }
-            }
-            _ => {}
-        }
-        None
-    }
-
-    /// Given a function block's `HirId`, returns its `FnDecl` if it exists, or `None` otherwise.
-    fn get_parent_fn_decl(&self, blk_id: hir::HirId) -> Option<(&'tcx hir::FnDecl<'tcx>, Ident)> {
-        let parent = self.tcx.hir().get(self.tcx.hir().get_parent_item(blk_id));
-        self.get_node_fn_decl(parent).map(|(fn_decl, ident, _)| (fn_decl, ident))
-    }
-
-    /// Given a function `Node`, return its `FnDecl` if it exists, or `None` otherwise.
-    pub(super) fn get_node_fn_decl(
-        &self,
-        node: Node<'tcx>,
-    ) -> Option<(&'tcx hir::FnDecl<'tcx>, Ident, bool)> {
-        match node {
-            Node::Item(&hir::Item { ident, kind: hir::ItemKind::Fn(ref sig, ..), .. }) => {
-                // This is less than ideal, it will not suggest a return type span on any
-                // method called `main`, regardless of whether it is actually the entry point,
-                // but it will still present it as the reason for the expected type.
-                Some((&sig.decl, ident, ident.name != sym::main))
-            }
-            Node::TraitItem(&hir::TraitItem {
-                ident,
-                kind: hir::TraitItemKind::Fn(ref sig, ..),
-                ..
-            }) => Some((&sig.decl, ident, true)),
-            Node::ImplItem(&hir::ImplItem {
-                ident,
-                kind: hir::ImplItemKind::Fn(ref sig, ..),
-                ..
-            }) => Some((&sig.decl, ident, false)),
-            _ => None,
-        }
-    }
-
-    /// Given a `HirId`, return the `FnDecl` of the method it is enclosed by and whether a
-    /// suggestion can be made, `None` otherwise.
-    pub fn get_fn_decl(&self, blk_id: hir::HirId) -> Option<(&'tcx hir::FnDecl<'tcx>, bool)> {
-        // Get enclosing Fn, if it is a function or a trait method, unless there's a `loop` or
-        // `while` before reaching it, as block tail returns are not available in them.
-        self.tcx.hir().get_return_block(blk_id).and_then(|blk_id| {
-            let parent = self.tcx.hir().get(blk_id);
-            self.get_node_fn_decl(parent).map(|(fn_decl, _, is_main)| (fn_decl, is_main))
-        })
-    }
-
-    /// On implicit return expressions with mismatched types, provides the following suggestions:
-    ///
-    /// - Points out the method's return type as the reason for the expected type.
-    /// - Possible missing semicolon.
-    /// - Possible missing return type if the return type is the default, and not `fn main()`.
-    pub fn suggest_mismatched_types_on_tail(
-        &self,
-        err: &mut DiagnosticBuilder<'_>,
-        expr: &'tcx hir::Expr<'tcx>,
-        expected: Ty<'tcx>,
-        found: Ty<'tcx>,
-        cause_span: Span,
-        blk_id: hir::HirId,
-    ) -> bool {
-        let expr = expr.peel_drop_temps();
-        self.suggest_missing_semicolon(err, expr, expected, cause_span);
-        let mut pointing_at_return_type = false;
-        if let Some((fn_decl, can_suggest)) = self.get_fn_decl(blk_id) {
-            pointing_at_return_type =
-                self.suggest_missing_return_type(err, &fn_decl, expected, found, can_suggest);
-        }
-        pointing_at_return_type
-    }
-
-    /// When encountering an fn-like ctor that needs to unify with a value, check whether calling
-    /// the ctor would successfully solve the type mismatch and if so, suggest it:
-    /// ```
-    /// fn foo(x: usize) -> usize { x }
-    /// let x: usize = foo;  // suggest calling the `foo` function: `foo(42)`
-    /// ```
-    fn suggest_fn_call(
-        &self,
-        err: &mut DiagnosticBuilder<'_>,
-        expr: &hir::Expr<'_>,
-        expected: Ty<'tcx>,
-        found: Ty<'tcx>,
-    ) -> bool {
-        let hir = self.tcx.hir();
-        let (def_id, sig) = match *found.kind() {
-            ty::FnDef(def_id, _) => (def_id, found.fn_sig(self.tcx)),
-            ty::Closure(def_id, substs) => (def_id, substs.as_closure().sig()),
-            _ => return false,
-        };
-
-        let sig = self.replace_bound_vars_with_fresh_vars(expr.span, infer::FnCall, &sig).0;
-        let sig = self.normalize_associated_types_in(expr.span, &sig);
-        if self.can_coerce(sig.output(), expected) {
-            let (mut sugg_call, applicability) = if sig.inputs().is_empty() {
-                (String::new(), Applicability::MachineApplicable)
-            } else {
-                ("...".to_string(), Applicability::HasPlaceholders)
-            };
-            let mut msg = "call this function";
-            match hir.get_if_local(def_id) {
-                Some(
-                    Node::Item(hir::Item { kind: ItemKind::Fn(.., body_id), .. })
-                    | Node::ImplItem(hir::ImplItem {
-                        kind: hir::ImplItemKind::Fn(_, body_id), ..
-                    })
-                    | Node::TraitItem(hir::TraitItem {
-                        kind: hir::TraitItemKind::Fn(.., hir::TraitFn::Provided(body_id)),
-                        ..
-                    }),
-                ) => {
-                    let body = hir.body(*body_id);
-                    sugg_call = body
-                        .params
-                        .iter()
-                        .map(|param| match &param.pat.kind {
-                            hir::PatKind::Binding(_, _, ident, None)
-                                if ident.name != kw::SelfLower =>
-                            {
-                                ident.to_string()
-                            }
-                            _ => "_".to_string(),
-                        })
-                        .collect::<Vec<_>>()
-                        .join(", ");
-                }
-                Some(Node::Expr(hir::Expr {
-                    kind: ExprKind::Closure(_, _, body_id, _, _),
-                    span: full_closure_span,
-                    ..
-                })) => {
-                    if *full_closure_span == expr.span {
-                        return false;
-                    }
-                    msg = "call this closure";
-                    let body = hir.body(*body_id);
-                    sugg_call = body
-                        .params
-                        .iter()
-                        .map(|param| match &param.pat.kind {
-                            hir::PatKind::Binding(_, _, ident, None)
-                                if ident.name != kw::SelfLower =>
-                            {
-                                ident.to_string()
-                            }
-                            _ => "_".to_string(),
-                        })
-                        .collect::<Vec<_>>()
-                        .join(", ");
-                }
-                Some(Node::Ctor(hir::VariantData::Tuple(fields, _))) => {
-                    sugg_call = fields.iter().map(|_| "_").collect::<Vec<_>>().join(", ");
-                    match def_id.as_local().map(|def_id| hir.def_kind(def_id)) {
-                        Some(DefKind::Ctor(hir::def::CtorOf::Variant, _)) => {
-                            msg = "instantiate this tuple variant";
-                        }
-                        Some(DefKind::Ctor(CtorOf::Struct, _)) => {
-                            msg = "instantiate this tuple struct";
-                        }
-                        _ => {}
-                    }
-                }
-                Some(Node::ForeignItem(hir::ForeignItem {
-                    kind: hir::ForeignItemKind::Fn(_, idents, _),
-                    ..
-                })) => {
-                    sugg_call = idents
-                        .iter()
-                        .map(|ident| {
-                            if ident.name != kw::SelfLower {
-                                ident.to_string()
-                            } else {
-                                "_".to_string()
-                            }
-                        })
-                        .collect::<Vec<_>>()
-                        .join(", ")
-                }
-                Some(Node::TraitItem(hir::TraitItem {
-                    kind: hir::TraitItemKind::Fn(.., hir::TraitFn::Required(idents)),
-                    ..
-                })) => {
-                    sugg_call = idents
-                        .iter()
-                        .map(|ident| {
-                            if ident.name != kw::SelfLower {
-                                ident.to_string()
-                            } else {
-                                "_".to_string()
-                            }
-                        })
-                        .collect::<Vec<_>>()
-                        .join(", ")
-                }
-                _ => {}
-            }
-            err.span_suggestion_verbose(
-                expr.span.shrink_to_hi(),
-                &format!("use parentheses to {}", msg),
-                format!("({})", sugg_call),
-                applicability,
-            );
-            return true;
-        }
-        false
-    }
-
-    pub fn suggest_deref_ref_or_into(
-        &self,
-        err: &mut DiagnosticBuilder<'_>,
-        expr: &hir::Expr<'_>,
-        expected: Ty<'tcx>,
-        found: Ty<'tcx>,
-        expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
-    ) {
-        if let Some((sp, msg, suggestion, applicability)) = self.check_ref(expr, found, expected) {
-            err.span_suggestion(sp, msg, suggestion, applicability);
-        } else if let (ty::FnDef(def_id, ..), true) =
-            (&found.kind(), self.suggest_fn_call(err, expr, expected, found))
-        {
-            if let Some(sp) = self.tcx.hir().span_if_local(*def_id) {
-                let sp = self.sess().source_map().guess_head_span(sp);
-                err.span_label(sp, &format!("{} defined here", found));
-            }
-        } else if !self.check_for_cast(err, expr, found, expected, expected_ty_expr) {
-            let is_struct_pat_shorthand_field =
-                self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, expr.span);
-            let methods = self.get_conversion_methods(expr.span, expected, found, expr.hir_id);
-            if let Ok(expr_text) = self.sess().source_map().span_to_snippet(expr.span) {
-                let mut suggestions = iter::repeat(&expr_text)
-                    .zip(methods.iter())
-                    .filter_map(|(receiver, method)| {
-                        let method_call = format!(".{}()", method.ident);
-                        if receiver.ends_with(&method_call) {
-                            None // do not suggest code that is already there (#53348)
-                        } else {
-                            let method_call_list = [".to_vec()", ".to_string()"];
-                            let sugg = if receiver.ends_with(".clone()")
-                                && method_call_list.contains(&method_call.as_str())
-                            {
-                                let max_len = receiver.rfind('.').unwrap();
-                                format!("{}{}", &receiver[..max_len], method_call)
-                            } else {
-                                if expr.precedence().order() < ExprPrecedence::MethodCall.order() {
-                                    format!("({}){}", receiver, method_call)
-                                } else {
-                                    format!("{}{}", receiver, method_call)
-                                }
-                            };
-                            Some(if is_struct_pat_shorthand_field {
-                                format!("{}: {}", receiver, sugg)
-                            } else {
-                                sugg
-                            })
-                        }
-                    })
-                    .peekable();
-                if suggestions.peek().is_some() {
-                    err.span_suggestions(
-                        expr.span,
-                        "try using a conversion method",
-                        suggestions,
-                        Applicability::MaybeIncorrect,
-                    );
-                }
-            }
-        }
-    }
-
-    /// When encountering the expected boxed value allocated in the stack, suggest allocating it
-    /// in the heap by calling `Box::new()`.
-    pub(super) fn suggest_boxing_when_appropriate(
-        &self,
-        err: &mut DiagnosticBuilder<'_>,
-        expr: &hir::Expr<'_>,
-        expected: Ty<'tcx>,
-        found: Ty<'tcx>,
-    ) {
-        if self.tcx.hir().is_inside_const_context(expr.hir_id) {
-            // Do not suggest `Box::new` in const context.
-            return;
-        }
-        if !expected.is_box() || found.is_box() {
-            return;
-        }
-        let boxed_found = self.tcx.mk_box(found);
-        if let (true, Ok(snippet)) = (
-            self.can_coerce(boxed_found, expected),
-            self.sess().source_map().span_to_snippet(expr.span),
-        ) {
-            err.span_suggestion(
-                expr.span,
-                "store this in the heap by calling `Box::new`",
-                format!("Box::new({})", snippet),
-                Applicability::MachineApplicable,
-            );
-            err.note(
-                "for more on the distinction between the stack and the heap, read \
-                 https://doc.rust-lang.org/book/ch15-01-box.html, \
-                 https://doc.rust-lang.org/rust-by-example/std/box.html, and \
-                 https://doc.rust-lang.org/std/boxed/index.html",
-            );
-        }
-    }
-
-    pub(super) fn note_internal_mutation_in_method(
-        &self,
-        err: &mut DiagnosticBuilder<'_>,
-        expr: &hir::Expr<'_>,
-        expected: Ty<'tcx>,
-        found: Ty<'tcx>,
-    ) {
-        if found != self.tcx.types.unit {
-            return;
-        }
-        if let ExprKind::MethodCall(path_segment, _, [rcvr, ..], _) = expr.kind {
-            if self
-                .typeck_results
-                .borrow()
-                .expr_ty_adjusted_opt(rcvr)
-                .map_or(true, |ty| expected.peel_refs() != ty.peel_refs())
-            {
-                return;
-            }
-            let mut sp = MultiSpan::from_span(path_segment.ident.span);
-            sp.push_span_label(
-                path_segment.ident.span,
-                format!(
-                    "this call modifies {} in-place",
-                    match rcvr.kind {
-                        ExprKind::Path(QPath::Resolved(
-                            None,
-                            hir::Path { segments: [segment], .. },
-                        )) => format!("`{}`", segment.ident),
-                        _ => "its receiver".to_string(),
-                    }
-                ),
-            );
-            sp.push_span_label(
-                rcvr.span,
-                "you probably want to use this value after calling the method...".to_string(),
-            );
-            err.span_note(
-                sp,
-                &format!("method `{}` modifies its receiver in-place", path_segment.ident),
-            );
-            err.note(&format!("...instead of the `()` output of method `{}`", path_segment.ident));
-        }
-    }
-
-    /// When encountering an `impl Future` where `BoxFuture` is expected, suggest `Box::pin`.
-    pub(super) fn suggest_calling_boxed_future_when_appropriate(
-        &self,
-        err: &mut DiagnosticBuilder<'_>,
-        expr: &hir::Expr<'_>,
-        expected: Ty<'tcx>,
-        found: Ty<'tcx>,
-    ) -> bool {
-        // Handle #68197.
-
-        if self.tcx.hir().is_inside_const_context(expr.hir_id) {
-            // Do not suggest `Box::new` in const context.
-            return false;
-        }
-        let pin_did = self.tcx.lang_items().pin_type();
-        match expected.kind() {
-            ty::Adt(def, _) if Some(def.did) != pin_did => return false,
-            // This guards the `unwrap` and `mk_box` below.
-            _ if pin_did.is_none() || self.tcx.lang_items().owned_box().is_none() => return false,
-            _ => {}
-        }
-        let boxed_found = self.tcx.mk_box(found);
-        let new_found = self.tcx.mk_lang_item(boxed_found, LangItem::Pin).unwrap();
-        if let (true, Ok(snippet)) = (
-            self.can_coerce(new_found, expected),
-            self.sess().source_map().span_to_snippet(expr.span),
-        ) {
-            match found.kind() {
-                ty::Adt(def, _) if def.is_box() => {
-                    err.help("use `Box::pin`");
-                }
-                _ => {
-                    err.span_suggestion(
-                        expr.span,
-                        "you need to pin and box this expression",
-                        format!("Box::pin({})", snippet),
-                        Applicability::MachineApplicable,
-                    );
-                }
-            }
-            true
-        } else {
-            false
-        }
-    }
-
-    /// A common error is to forget to add a semicolon at the end of a block, e.g.,
-    ///
-    /// ```
-    /// fn foo() {
-    ///     bar_that_returns_u32()
-    /// }
-    /// ```
-    ///
-    /// This routine checks if the return expression in a block would make sense on its own as a
-    /// statement and the return type has been left as default or has been specified as `()`. If so,
-    /// it suggests adding a semicolon.
-    fn suggest_missing_semicolon(
-        &self,
-        err: &mut DiagnosticBuilder<'_>,
-        expression: &'tcx hir::Expr<'tcx>,
-        expected: Ty<'tcx>,
-        cause_span: Span,
-    ) {
-        if expected.is_unit() {
-            // `BlockTailExpression` only relevant if the tail expr would be
-            // useful on its own.
-            match expression.kind {
-                ExprKind::Call(..)
-                | ExprKind::MethodCall(..)
-                | ExprKind::Loop(..)
-                | ExprKind::Match(..)
-                | ExprKind::Block(..) => {
-                    err.span_suggestion(
-                        cause_span.shrink_to_hi(),
-                        "try adding a semicolon",
-                        ";".to_string(),
-                        Applicability::MachineApplicable,
-                    );
-                }
-                _ => (),
-            }
-        }
-    }
-
-    /// A possible error is to forget to add a return type that is needed:
-    ///
-    /// ```
-    /// fn foo() {
-    ///     bar_that_returns_u32()
-    /// }
-    /// ```
-    ///
-    /// This routine checks if the return type is left as default, the method is not part of an
-    /// `impl` block and that it isn't the `main` method. If so, it suggests setting the return
-    /// type.
-    pub(super) fn suggest_missing_return_type(
-        &self,
-        err: &mut DiagnosticBuilder<'_>,
-        fn_decl: &hir::FnDecl<'_>,
-        expected: Ty<'tcx>,
-        found: Ty<'tcx>,
-        can_suggest: bool,
-    ) -> bool {
-        // Only suggest changing the return type for methods that
-        // haven't set a return type at all (and aren't `fn main()` or an impl).
-        match (&fn_decl.output, found.is_suggestable(), can_suggest, expected.is_unit()) {
-            (&hir::FnRetTy::DefaultReturn(span), true, true, true) => {
-                err.span_suggestion(
-                    span,
-                    "try adding a return type",
-                    format!("-> {} ", self.resolve_vars_with_obligations(found)),
-                    Applicability::MachineApplicable,
-                );
-                true
-            }
-            (&hir::FnRetTy::DefaultReturn(span), false, true, true) => {
-                err.span_label(span, "possibly return type missing here?");
-                true
-            }
-            (&hir::FnRetTy::DefaultReturn(span), _, false, true) => {
-                // `fn main()` must return `()`, do not suggest changing return type
-                err.span_label(span, "expected `()` because of default return type");
-                true
-            }
-            // expectation was caused by something else, not the default return
-            (&hir::FnRetTy::DefaultReturn(_), _, _, false) => false,
-            (&hir::FnRetTy::Return(ref ty), _, _, _) => {
-                // Only point to return type if the expected type is the return type, as if they
-                // are not, the expectation must have been caused by something else.
-                debug!("suggest_missing_return_type: return type {:?} node {:?}", ty, ty.kind);
-                let sp = ty.span;
-                let ty = AstConv::ast_ty_to_ty(self, ty);
-                debug!("suggest_missing_return_type: return type {:?}", ty);
-                debug!("suggest_missing_return_type: expected type {:?}", ty);
-                if ty.kind() == expected.kind() {
-                    err.span_label(sp, format!("expected `{}` because of return type", expected));
-                    return true;
-                }
-                false
-            }
-        }
-    }
-
-    /// A possible error is to forget to add `.await` when using futures:
-    ///
-    /// ```
-    /// async fn make_u32() -> u32 {
-    ///     22
-    /// }
-    ///
-    /// fn take_u32(x: u32) {}
-    ///
-    /// async fn foo() {
-    ///     let x = make_u32();
-    ///     take_u32(x);
-    /// }
-    /// ```
-    ///
-    /// This routine checks if the found type `T` implements `Future<Output=U>` where `U` is the
-    /// expected type. If this is the case, and we are inside of an async body, it suggests adding
-    /// `.await` to the tail of the expression.
-    pub(super) fn suggest_missing_await(
-        &self,
-        err: &mut DiagnosticBuilder<'_>,
-        expr: &hir::Expr<'_>,
-        expected: Ty<'tcx>,
-        found: Ty<'tcx>,
-    ) {
-        debug!("suggest_missing_await: expr={:?} expected={:?}, found={:?}", expr, expected, found);
-        // `.await` is not permitted outside of `async` bodies, so don't bother to suggest if the
-        // body isn't `async`.
-        let item_id = self.tcx().hir().get_parent_node(self.body_id);
-        if let Some(body_id) = self.tcx().hir().maybe_body_owned_by(item_id) {
-            let body = self.tcx().hir().body(body_id);
-            if let Some(hir::GeneratorKind::Async(_)) = body.generator_kind {
-                let sp = expr.span;
-                // Check for `Future` implementations by constructing a predicate to
-                // prove: `<T as Future>::Output == U`
-                let future_trait = self.tcx.require_lang_item(LangItem::Future, Some(sp));
-                let item_def_id = self
-                    .tcx
-                    .associated_items(future_trait)
-                    .in_definition_order()
-                    .next()
-                    .unwrap()
-                    .def_id;
-                // `<T as Future>::Output`
-                let projection_ty = ty::ProjectionTy {
-                    // `T`
-                    substs: self
-                        .tcx
-                        .mk_substs_trait(found, self.fresh_substs_for_item(sp, item_def_id)),
-                    // `Future::Output`
-                    item_def_id,
-                };
-
-                let predicate = ty::PredicateAtom::Projection(ty::ProjectionPredicate {
-                    projection_ty,
-                    ty: expected,
-                })
-                .potentially_quantified(self.tcx, ty::PredicateKind::ForAll);
-                let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
-
-                debug!("suggest_missing_await: trying obligation {:?}", obligation);
-
-                if self.infcx.predicate_may_hold(&obligation) {
-                    debug!("suggest_missing_await: obligation held: {:?}", obligation);
-                    if let Ok(code) = self.sess().source_map().span_to_snippet(sp) {
-                        err.span_suggestion(
-                            sp,
-                            "consider using `.await` here",
-                            format!("{}.await", code),
-                            Applicability::MaybeIncorrect,
-                        );
-                    } else {
-                        debug!("suggest_missing_await: no snippet for {:?}", sp);
-                    }
-                } else {
-                    debug!("suggest_missing_await: obligation did not hold: {:?}", obligation)
-                }
-            }
-        }
-    }
-
-    pub(super) fn suggest_missing_parentheses(
-        &self,
-        err: &mut DiagnosticBuilder<'_>,
-        expr: &hir::Expr<'_>,
-    ) {
-        let sp = self.tcx.sess.source_map().start_point(expr.span);
-        if let Some(sp) = self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp) {
-            // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`
-            self.tcx.sess.parse_sess.expr_parentheses_needed(err, *sp, None);
-        }
-    }
-
-    pub(super) fn note_need_for_fn_pointer(
-        &self,
-        err: &mut DiagnosticBuilder<'_>,
-        expected: Ty<'tcx>,
-        found: Ty<'tcx>,
-    ) {
-        let (sig, did, substs) = match (&expected.kind(), &found.kind()) {
-            (ty::FnDef(did1, substs1), ty::FnDef(did2, substs2)) => {
-                let sig1 = self.tcx.fn_sig(*did1).subst(self.tcx, substs1);
-                let sig2 = self.tcx.fn_sig(*did2).subst(self.tcx, substs2);
-                if sig1 != sig2 {
-                    return;
-                }
-                err.note(
-                    "different `fn` items always have unique types, even if their signatures are \
-                     the same",
-                );
-                (sig1, *did1, substs1)
-            }
-            (ty::FnDef(did, substs), ty::FnPtr(sig2)) => {
-                let sig1 = self.tcx.fn_sig(*did).subst(self.tcx, substs);
-                if sig1 != *sig2 {
-                    return;
-                }
-                (sig1, *did, substs)
-            }
-            _ => return,
-        };
-        err.help(&format!("change the expected type to be function pointer `{}`", sig));
-        err.help(&format!(
-            "if the expected type is due to type inference, cast the expected `fn` to a function \
-             pointer: `{} as {}`",
-            self.tcx.def_path_str_with_substs(did, substs),
-            sig
-        ));
-    }
-
-    /// A common error is to add an extra semicolon:
-    ///
-    /// ```
-    /// fn foo() -> usize {
-    ///     22;
-    /// }
-    /// ```
-    ///
-    /// This routine checks if the final statement in a block is an
-    /// expression with an explicit semicolon whose type is compatible
-    /// with `expected_ty`. If so, it suggests removing the semicolon.
-    fn consider_hint_about_removing_semicolon(
-        &self,
-        blk: &'tcx hir::Block<'tcx>,
-        expected_ty: Ty<'tcx>,
-        err: &mut DiagnosticBuilder<'_>,
-    ) {
-        if let Some(span_semi) = self.could_remove_semicolon(blk, expected_ty) {
-            err.span_suggestion(
-                span_semi,
-                "consider removing this semicolon",
-                String::new(),
-                Applicability::MachineApplicable,
-            );
-        }
-    }
-
-    pub(super) fn could_remove_semicolon(
-        &self,
-        blk: &'tcx hir::Block<'tcx>,
-        expected_ty: Ty<'tcx>,
-    ) -> Option<Span> {
-        // Be helpful when the user wrote `{... expr;}` and
-        // taking the `;` off is enough to fix the error.
-        let last_stmt = blk.stmts.last()?;
-        let last_expr = match last_stmt.kind {
-            hir::StmtKind::Semi(ref e) => e,
-            _ => return None,
-        };
-        let last_expr_ty = self.node_ty(last_expr.hir_id);
-        if matches!(last_expr_ty.kind(), ty::Error(_))
-            || self.can_sub(self.param_env, last_expr_ty, expected_ty).is_err()
-        {
-            return None;
-        }
-        let original_span = original_sp(last_stmt.span, blk.span);
-        Some(original_span.with_lo(original_span.hi() - BytePos(1)))
-    }
-
-    // Instantiates the given path, which must refer to an item with the given
-    // number of type parameters and type.
-    pub fn instantiate_value_path(
-        &self,
-        segments: &[hir::PathSegment<'_>],
-        self_ty: Option<Ty<'tcx>>,
-        res: Res,
-        span: Span,
-        hir_id: hir::HirId,
-    ) -> (Ty<'tcx>, Res) {
-        debug!(
-            "instantiate_value_path(segments={:?}, self_ty={:?}, res={:?}, hir_id={})",
-            segments, self_ty, res, hir_id,
-        );
-
-        let tcx = self.tcx;
-
-        let path_segs = match res {
-            Res::Local(_) | Res::SelfCtor(_) => vec![],
-            Res::Def(kind, def_id) => {
-                AstConv::def_ids_for_value_path_segments(self, segments, self_ty, kind, def_id)
-            }
-            _ => bug!("instantiate_value_path on {:?}", res),
-        };
-
-        let mut user_self_ty = None;
-        let mut is_alias_variant_ctor = false;
-        match res {
-            Res::Def(DefKind::Ctor(CtorOf::Variant, _), _) => {
-                if let Some(self_ty) = self_ty {
-                    let adt_def = self_ty.ty_adt_def().unwrap();
-                    user_self_ty = Some(UserSelfTy { impl_def_id: adt_def.did, self_ty });
-                    is_alias_variant_ctor = true;
-                }
-            }
-            Res::Def(DefKind::AssocFn | DefKind::AssocConst, def_id) => {
-                let container = tcx.associated_item(def_id).container;
-                debug!("instantiate_value_path: def_id={:?} container={:?}", def_id, container);
-                match container {
-                    ty::TraitContainer(trait_did) => {
-                        callee::check_legal_trait_for_method_call(tcx, span, None, trait_did)
-                    }
-                    ty::ImplContainer(impl_def_id) => {
-                        if segments.len() == 1 {
-                            // `<T>::assoc` will end up here, and so
-                            // can `T::assoc`. It this came from an
-                            // inherent impl, we need to record the
-                            // `T` for posterity (see `UserSelfTy` for
-                            // details).
-                            let self_ty = self_ty.expect("UFCS sugared assoc missing Self");
-                            user_self_ty = Some(UserSelfTy { impl_def_id, self_ty });
-                        }
-                    }
-                }
-            }
-            _ => {}
-        }
-
-        // Now that we have categorized what space the parameters for each
-        // segment belong to, let's sort out the parameters that the user
-        // provided (if any) into their appropriate spaces. We'll also report
-        // errors if type parameters are provided in an inappropriate place.
-
-        let generic_segs: FxHashSet<_> = path_segs.iter().map(|PathSeg(_, index)| index).collect();
-        let generics_has_err = AstConv::prohibit_generics(
-            self,
-            segments.iter().enumerate().filter_map(|(index, seg)| {
-                if !generic_segs.contains(&index) || is_alias_variant_ctor {
-                    Some(seg)
-                } else {
-                    None
-                }
-            }),
-        );
-
-        if let Res::Local(hid) = res {
-            let ty = self.local_ty(span, hid).decl_ty;
-            let ty = self.normalize_associated_types_in(span, &ty);
-            self.write_ty(hir_id, ty);
-            return (ty, res);
-        }
-
-        if generics_has_err {
-            // Don't try to infer type parameters when prohibited generic arguments were given.
-            user_self_ty = None;
-        }
-
-        // Now we have to compare the types that the user *actually*
-        // provided against the types that were *expected*. If the user
-        // did not provide any types, then we want to substitute inference
-        // variables. If the user provided some types, we may still need
-        // to add defaults. If the user provided *too many* types, that's
-        // a problem.
-
-        let mut infer_args_for_err = FxHashSet::default();
-        for &PathSeg(def_id, index) in &path_segs {
-            let seg = &segments[index];
-            let generics = tcx.generics_of(def_id);
-            // Argument-position `impl Trait` is treated as a normal generic
-            // parameter internally, but we don't allow users to specify the
-            // parameter's value explicitly, so we have to do some error-
-            // checking here.
-            if let GenericArgCountResult {
-                correct: Err(GenericArgCountMismatch { reported: Some(ErrorReported), .. }),
-                ..
-            } = AstConv::check_generic_arg_count_for_call(
-                tcx, span, &generics, &seg, false, // `is_method_call`
-            ) {
-                infer_args_for_err.insert(index);
-                self.set_tainted_by_errors(); // See issue #53251.
-            }
-        }
-
-        let has_self = path_segs
-            .last()
-            .map(|PathSeg(def_id, _)| tcx.generics_of(*def_id).has_self)
-            .unwrap_or(false);
-
-        let (res, self_ctor_substs) = if let Res::SelfCtor(impl_def_id) = res {
-            let ty = self.normalize_ty(span, tcx.at(span).type_of(impl_def_id));
-            match *ty.kind() {
-                ty::Adt(adt_def, substs) if adt_def.has_ctor() => {
-                    let variant = adt_def.non_enum_variant();
-                    let ctor_def_id = variant.ctor_def_id.unwrap();
-                    (
-                        Res::Def(DefKind::Ctor(CtorOf::Struct, variant.ctor_kind), ctor_def_id),
-                        Some(substs),
-                    )
-                }
-                _ => {
-                    let mut err = tcx.sess.struct_span_err(
-                        span,
-                        "the `Self` constructor can only be used with tuple or unit structs",
-                    );
-                    if let Some(adt_def) = ty.ty_adt_def() {
-                        match adt_def.adt_kind() {
-                            AdtKind::Enum => {
-                                err.help("did you mean to use one of the enum's variants?");
-                            }
-                            AdtKind::Struct | AdtKind::Union => {
-                                err.span_suggestion(
-                                    span,
-                                    "use curly brackets",
-                                    String::from("Self { /* fields */ }"),
-                                    Applicability::HasPlaceholders,
-                                );
-                            }
-                        }
-                    }
-                    err.emit();
-
-                    return (tcx.ty_error(), res);
-                }
-            }
-        } else {
-            (res, None)
-        };
-        let def_id = res.def_id();
-
-        // The things we are substituting into the type should not contain
-        // escaping late-bound regions, and nor should the base type scheme.
-        let ty = tcx.type_of(def_id);
-
-        let arg_count = GenericArgCountResult {
-            explicit_late_bound: ExplicitLateBound::No,
-            correct: if infer_args_for_err.is_empty() {
-                Ok(())
-            } else {
-                Err(GenericArgCountMismatch::default())
-            },
-        };
-
-        let substs = self_ctor_substs.unwrap_or_else(|| {
-            AstConv::create_substs_for_generic_args(
-                tcx,
-                def_id,
-                &[][..],
-                has_self,
-                self_ty,
-                arg_count,
-                // Provide the generic args, and whether types should be inferred.
-                |def_id| {
-                    if let Some(&PathSeg(_, index)) =
-                        path_segs.iter().find(|&PathSeg(did, _)| *did == def_id)
-                    {
-                        // If we've encountered an `impl Trait`-related error, we're just
-                        // going to infer the arguments for better error messages.
-                        if !infer_args_for_err.contains(&index) {
-                            // Check whether the user has provided generic arguments.
-                            if let Some(ref data) = segments[index].args {
-                                return (Some(data), segments[index].infer_args);
-                            }
-                        }
-                        return (None, segments[index].infer_args);
-                    }
-
-                    (None, true)
-                },
-                // Provide substitutions for parameters for which (valid) arguments have been provided.
-                |param, arg| match (&param.kind, arg) {
-                    (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
-                        AstConv::ast_region_to_region(self, lt, Some(param)).into()
-                    }
-                    (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
-                        self.to_ty(ty).into()
-                    }
-                    (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
-                        self.const_arg_to_const(&ct.value, param.def_id).into()
-                    }
-                    _ => unreachable!(),
-                },
-                // Provide substitutions for parameters for which arguments are inferred.
-                |substs, param, infer_args| {
-                    match param.kind {
-                        GenericParamDefKind::Lifetime => {
-                            self.re_infer(Some(param), span).unwrap().into()
-                        }
-                        GenericParamDefKind::Type { has_default, .. } => {
-                            if !infer_args && has_default {
-                                // If we have a default, then we it doesn't matter that we're not
-                                // inferring the type arguments: we provide the default where any
-                                // is missing.
-                                let default = tcx.type_of(param.def_id);
-                                self.normalize_ty(
-                                    span,
-                                    default.subst_spanned(tcx, substs.unwrap(), Some(span)),
-                                )
-                                .into()
-                            } else {
-                                // If no type arguments were provided, we have to infer them.
-                                // This case also occurs as a result of some malformed input, e.g.
-                                // a lifetime argument being given instead of a type parameter.
-                                // Using inference instead of `Error` gives better error messages.
-                                self.var_for_def(span, param)
-                            }
-                        }
-                        GenericParamDefKind::Const => {
-                            // FIXME(const_generics:defaults)
-                            // No const parameters were provided, we have to infer them.
-                            self.var_for_def(span, param)
-                        }
-                    }
-                },
-            )
-        });
-        assert!(!substs.has_escaping_bound_vars());
-        assert!(!ty.has_escaping_bound_vars());
-
-        // First, store the "user substs" for later.
-        self.write_user_type_annotation_from_substs(hir_id, def_id, substs, user_self_ty);
-
-        self.add_required_obligations(span, def_id, &substs);
-
-        // Substitute the values for the type parameters into the type of
-        // the referenced item.
-        let ty_substituted = self.instantiate_type_scheme(span, &substs, &ty);
-
-        if let Some(UserSelfTy { impl_def_id, self_ty }) = user_self_ty {
-            // In the case of `Foo<T>::method` and `<Foo<T>>::method`, if `method`
-            // is inherent, there is no `Self` parameter; instead, the impl needs
-            // type parameters, which we can infer by unifying the provided `Self`
-            // with the substituted impl type.
-            // This also occurs for an enum variant on a type alias.
-            let ty = tcx.type_of(impl_def_id);
-
-            let impl_ty = self.instantiate_type_scheme(span, &substs, &ty);
-            match self.at(&self.misc(span), self.param_env).sup(impl_ty, self_ty) {
-                Ok(ok) => self.register_infer_ok_obligations(ok),
-                Err(_) => {
-                    self.tcx.sess.delay_span_bug(
-                        span,
-                        &format!(
-                        "instantiate_value_path: (UFCS) {:?} was a subtype of {:?} but now is not?",
-                        self_ty,
-                        impl_ty,
-                    ),
-                    );
-                }
-            }
-        }
-
-        self.check_rustc_args_require_const(def_id, hir_id, span);
-
-        debug!("instantiate_value_path: type of {:?} is {:?}", hir_id, ty_substituted);
-        self.write_substs(hir_id, substs);
-
-        (ty_substituted, res)
-    }
-
-    /// Add all the obligations that are required, substituting and normalized appropriately.
-    fn add_required_obligations(&self, span: Span, def_id: DefId, substs: &SubstsRef<'tcx>) {
-        let (bounds, spans) = self.instantiate_bounds(span, def_id, &substs);
-
-        for (i, mut obligation) in traits::predicates_for_generics(
-            traits::ObligationCause::new(span, self.body_id, traits::ItemObligation(def_id)),
-            self.param_env,
-            bounds,
-        )
-        .enumerate()
-        {
-            // This makes the error point at the bound, but we want to point at the argument
-            if let Some(span) = spans.get(i) {
-                obligation.cause.make_mut().code = traits::BindingObligation(def_id, *span);
-            }
-            self.register_predicate(obligation);
-        }
-    }
-
-    fn check_rustc_args_require_const(&self, def_id: DefId, hir_id: hir::HirId, span: Span) {
-        // We're only interested in functions tagged with
-        // #[rustc_args_required_const], so ignore anything that's not.
-        if !self.tcx.has_attr(def_id, sym::rustc_args_required_const) {
-            return;
-        }
-
-        // If our calling expression is indeed the function itself, we're good!
-        // If not, generate an error that this can only be called directly.
-        if let Node::Expr(expr) = self.tcx.hir().get(self.tcx.hir().get_parent_node(hir_id)) {
-            if let ExprKind::Call(ref callee, ..) = expr.kind {
-                if callee.hir_id == hir_id {
-                    return;
-                }
-            }
-        }
-
-        self.tcx.sess.span_err(
-            span,
-            "this function can only be invoked directly, not through a function pointer",
-        );
-    }
-
-    /// Resolves `typ` by a single level if `typ` is a type variable.
-    /// If no resolution is possible, then an error is reported.
-    /// Numeric inference variables may be left unresolved.
-    pub fn structurally_resolved_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
-        let ty = self.resolve_vars_with_obligations(ty);
-        if !ty.is_ty_var() {
-            ty
-        } else {
-            if !self.is_tainted_by_errors() {
-                self.emit_inference_failure_err((**self).body_id, sp, ty.into(), E0282)
-                    .note("type must be known at this point")
-                    .emit();
-            }
-            let err = self.tcx.ty_error();
-            self.demand_suptype(sp, err, ty);
-            err
-        }
-    }
-
-    pub(super) fn with_breakable_ctxt<F: FnOnce() -> R, R>(
-        &self,
-        id: hir::HirId,
-        ctxt: BreakableCtxt<'tcx>,
-        f: F,
-    ) -> (BreakableCtxt<'tcx>, R) {
-        let index;
-        {
-            let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
-            index = enclosing_breakables.stack.len();
-            enclosing_breakables.by_id.insert(id, index);
-            enclosing_breakables.stack.push(ctxt);
-        }
-        let result = f();
-        let ctxt = {
-            let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
-            debug_assert!(enclosing_breakables.stack.len() == index + 1);
-            enclosing_breakables.by_id.remove(&id).expect("missing breakable context");
-            enclosing_breakables.stack.pop().expect("missing breakable context")
-        };
-        (ctxt, result)
-    }
-
-    /// Instantiate a QueryResponse in a probe context, without a
-    /// good ObligationCause.
-    pub(super) fn probe_instantiate_query_response(
-        &self,
-        span: Span,
-        original_values: &OriginalQueryValues<'tcx>,
-        query_result: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>,
-    ) -> InferResult<'tcx, Ty<'tcx>> {
-        self.instantiate_query_response_and_region_obligations(
-            &traits::ObligationCause::misc(span, self.body_id),
-            self.param_env,
-            original_values,
-            query_result,
-        )
-    }
-
-    /// Returns `true` if an expression is contained inside the LHS of an assignment expression.
-    pub(super) fn expr_in_place(&self, mut expr_id: hir::HirId) -> bool {
-        let mut contained_in_place = false;
-
-        while let hir::Node::Expr(parent_expr) =
-            self.tcx.hir().get(self.tcx.hir().get_parent_node(expr_id))
-        {
-            match &parent_expr.kind {
-                hir::ExprKind::Assign(lhs, ..) | hir::ExprKind::AssignOp(_, lhs, ..) => {
-                    if lhs.hir_id == expr_id {
-                        contained_in_place = true;
-                        break;
-                    }
-                }
-                _ => (),
-            }
-            expr_id = parent_expr.hir_id;
-        }
-
-        contained_in_place
-    }
-}
-impl<'a, 'tcx> Deref for FnCtxt<'a, 'tcx> {
-    type Target = Inherited<'a, 'tcx>;
-    fn deref(&self) -> &Self::Target {
-        &self.inh
-    }
-}
-
-impl<'a, 'tcx> AstConv<'tcx> for FnCtxt<'a, 'tcx> {
-    fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
-        self.tcx
-    }
-
-    fn item_def_id(&self) -> Option<DefId> {
-        None
-    }
-
-    fn default_constness_for_trait_bounds(&self) -> hir::Constness {
-        // FIXME: refactor this into a method
-        let node = self.tcx.hir().get(self.body_id);
-        if let Some(fn_like) = FnLikeNode::from_node(node) {
-            fn_like.constness()
-        } else {
-            hir::Constness::NotConst
-        }
-    }
-
-    fn get_type_parameter_bounds(&self, _: Span, def_id: DefId) -> ty::GenericPredicates<'tcx> {
-        let tcx = self.tcx;
-        let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
-        let item_id = tcx.hir().ty_param_owner(hir_id);
-        let item_def_id = tcx.hir().local_def_id(item_id);
-        let generics = tcx.generics_of(item_def_id);
-        let index = generics.param_def_id_to_index[&def_id];
-        ty::GenericPredicates {
-            parent: None,
-            predicates: tcx.arena.alloc_from_iter(
-                self.param_env.caller_bounds().iter().filter_map(|predicate| {
-                    match predicate.skip_binders() {
-                        ty::PredicateAtom::Trait(data, _) if data.self_ty().is_param(index) => {
-                            // HACK(eddyb) should get the original `Span`.
-                            let span = tcx.def_span(def_id);
-                            Some((predicate, span))
-                        }
-                        _ => None,
-                    }
-                }),
-            ),
-        }
-    }
-
-    fn re_infer(&self, def: Option<&ty::GenericParamDef>, span: Span) -> Option<ty::Region<'tcx>> {
-        let v = match def {
-            Some(def) => infer::EarlyBoundRegion(span, def.name),
-            None => infer::MiscVariable(span),
-        };
-        Some(self.next_region_var(v))
-    }
-
-    fn allow_ty_infer(&self) -> bool {
-        true
-    }
-
-    fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
-        if let Some(param) = param {
-            if let GenericArgKind::Type(ty) = self.var_for_def(span, param).unpack() {
-                return ty;
-            }
-            unreachable!()
-        } else {
-            self.next_ty_var(TypeVariableOrigin {
-                kind: TypeVariableOriginKind::TypeInference,
-                span,
-            })
-        }
-    }
-
-    fn ct_infer(
-        &self,
-        ty: Ty<'tcx>,
-        param: Option<&ty::GenericParamDef>,
-        span: Span,
-    ) -> &'tcx Const<'tcx> {
-        if let Some(param) = param {
-            if let GenericArgKind::Const(ct) = self.var_for_def(span, param).unpack() {
-                return ct;
-            }
-            unreachable!()
-        } else {
-            self.next_const_var(
-                ty,
-                ConstVariableOrigin { kind: ConstVariableOriginKind::ConstInference, span },
-            )
-        }
-    }
-
-    fn projected_ty_from_poly_trait_ref(
-        &self,
-        span: Span,
-        item_def_id: DefId,
-        item_segment: &hir::PathSegment<'_>,
-        poly_trait_ref: ty::PolyTraitRef<'tcx>,
-    ) -> Ty<'tcx> {
-        let (trait_ref, _) = self.replace_bound_vars_with_fresh_vars(
-            span,
-            infer::LateBoundRegionConversionTime::AssocTypeProjection(item_def_id),
-            &poly_trait_ref,
-        );
-
-        let item_substs = <dyn AstConv<'tcx>>::create_substs_for_associated_item(
-            self,
-            self.tcx,
-            span,
-            item_def_id,
-            item_segment,
-            trait_ref.substs,
-        );
-
-        self.tcx().mk_projection(item_def_id, item_substs)
-    }
-
-    fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
-        if ty.has_escaping_bound_vars() {
-            ty // FIXME: normalization and escaping regions
-        } else {
-            self.normalize_associated_types_in(span, &ty)
-        }
-    }
-
-    fn set_tainted_by_errors(&self) {
-        self.infcx.set_tainted_by_errors()
-    }
-
-    fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, _span: Span) {
-        self.write_ty(hir_id, ty)
-    }
-}
diff --git a/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs b/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
new file mode 100644
index 00000000000..017b0abd1d6
--- /dev/null
+++ b/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
@@ -0,0 +1,1469 @@
+use crate::astconv::{
+    AstConv, ExplicitLateBound, GenericArgCountMismatch, GenericArgCountResult, PathSeg,
+};
+use crate::check::callee::{self, DeferredCallResolution};
+use crate::check::method::{self, MethodCallee, SelfSource};
+use crate::check::{BreakableCtxt, Diverges, Expectation, FallbackMode, FnCtxt, LocalTy};
+
+use rustc_data_structures::captures::Captures;
+use rustc_data_structures::fx::FxHashSet;
+use rustc_errors::{Applicability, DiagnosticBuilder, ErrorReported};
+use rustc_hir as hir;
+use rustc_hir::def::{CtorOf, DefKind, Res};
+use rustc_hir::def_id::DefId;
+use rustc_hir::lang_items::LangItem;
+use rustc_hir::{ExprKind, GenericArg, Node, QPath};
+use rustc_infer::infer::canonical::{Canonical, OriginalQueryValues, QueryResponse};
+use rustc_infer::infer::error_reporting::TypeAnnotationNeeded::E0282;
+use rustc_infer::infer::{InferOk, InferResult};
+use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
+use rustc_middle::ty::fold::TypeFoldable;
+use rustc_middle::ty::subst::{
+    self, GenericArgKind, InternalSubsts, Subst, SubstsRef, UserSelfTy, UserSubsts,
+};
+use rustc_middle::ty::{
+    self, AdtKind, CanonicalUserType, DefIdTree, GenericParamDefKind, ToPolyTraitRef, ToPredicate,
+    Ty, UserType,
+};
+use rustc_session::lint;
+use rustc_span::hygiene::DesugaringKind;
+use rustc_span::source_map::{original_sp, DUMMY_SP};
+use rustc_span::symbol::{kw, sym, Ident};
+use rustc_span::{self, BytePos, MultiSpan, Span};
+use rustc_trait_selection::infer::InferCtxtExt as _;
+use rustc_trait_selection::opaque_types::InferCtxtExt as _;
+use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
+use rustc_trait_selection::traits::{self, ObligationCauseCode, TraitEngine, TraitEngineExt};
+
+use std::collections::hash_map::Entry;
+use std::slice;
+
+impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
+    /// Produces warning on the given node, if the current point in the
+    /// function is unreachable, and there hasn't been another warning.
+    pub(in super::super) fn warn_if_unreachable(&self, id: hir::HirId, span: Span, kind: &str) {
+        // FIXME: Combine these two 'if' expressions into one once
+        // let chains are implemented
+        if let Diverges::Always { span: orig_span, custom_note } = self.diverges.get() {
+            // If span arose from a desugaring of `if` or `while`, then it is the condition itself,
+            // which diverges, that we are about to lint on. This gives suboptimal diagnostics.
+            // Instead, stop here so that the `if`- or `while`-expression's block is linted instead.
+            if !span.is_desugaring(DesugaringKind::CondTemporary)
+                && !span.is_desugaring(DesugaringKind::Async)
+                && !orig_span.is_desugaring(DesugaringKind::Await)
+            {
+                self.diverges.set(Diverges::WarnedAlways);
+
+                debug!("warn_if_unreachable: id={:?} span={:?} kind={}", id, span, kind);
+
+                self.tcx().struct_span_lint_hir(lint::builtin::UNREACHABLE_CODE, id, span, |lint| {
+                    let msg = format!("unreachable {}", kind);
+                    lint.build(&msg)
+                        .span_label(span, &msg)
+                        .span_label(
+                            orig_span,
+                            custom_note
+                                .unwrap_or("any code following this expression is unreachable"),
+                        )
+                        .emit();
+                })
+            }
+        }
+    }
+
+    /// Resolves type and const variables in `ty` if possible. Unlike the infcx
+    /// version (resolve_vars_if_possible), this version will
+    /// also select obligations if it seems useful, in an effort
+    /// to get more type information.
+    pub(in super::super) fn resolve_vars_with_obligations(&self, mut ty: Ty<'tcx>) -> Ty<'tcx> {
+        debug!("resolve_vars_with_obligations(ty={:?})", ty);
+
+        // No Infer()? Nothing needs doing.
+        if !ty.has_infer_types_or_consts() {
+            debug!("resolve_vars_with_obligations: ty={:?}", ty);
+            return ty;
+        }
+
+        // If `ty` is a type variable, see whether we already know what it is.
+        ty = self.resolve_vars_if_possible(&ty);
+        if !ty.has_infer_types_or_consts() {
+            debug!("resolve_vars_with_obligations: ty={:?}", ty);
+            return ty;
+        }
+
+        // If not, try resolving pending obligations as much as
+        // possible. This can help substantially when there are
+        // indirect dependencies that don't seem worth tracking
+        // precisely.
+        self.select_obligations_where_possible(false, |_| {});
+        ty = self.resolve_vars_if_possible(&ty);
+
+        debug!("resolve_vars_with_obligations: ty={:?}", ty);
+        ty
+    }
+
+    pub(in super::super) fn record_deferred_call_resolution(
+        &self,
+        closure_def_id: DefId,
+        r: DeferredCallResolution<'tcx>,
+    ) {
+        let mut deferred_call_resolutions = self.deferred_call_resolutions.borrow_mut();
+        deferred_call_resolutions.entry(closure_def_id).or_default().push(r);
+    }
+
+    pub(in super::super) fn remove_deferred_call_resolutions(
+        &self,
+        closure_def_id: DefId,
+    ) -> Vec<DeferredCallResolution<'tcx>> {
+        let mut deferred_call_resolutions = self.deferred_call_resolutions.borrow_mut();
+        deferred_call_resolutions.remove(&closure_def_id).unwrap_or(vec![])
+    }
+
+    pub fn tag(&self) -> String {
+        format!("{:p}", self)
+    }
+
+    pub fn local_ty(&self, span: Span, nid: hir::HirId) -> LocalTy<'tcx> {
+        self.locals.borrow().get(&nid).cloned().unwrap_or_else(|| {
+            span_bug!(span, "no type for local variable {}", self.tcx.hir().node_to_string(nid))
+        })
+    }
+
+    #[inline]
+    pub fn write_ty(&self, id: hir::HirId, ty: Ty<'tcx>) {
+        debug!(
+            "write_ty({:?}, {:?}) in fcx {}",
+            id,
+            self.resolve_vars_if_possible(&ty),
+            self.tag()
+        );
+        self.typeck_results.borrow_mut().node_types_mut().insert(id, ty);
+
+        if ty.references_error() {
+            self.has_errors.set(true);
+            self.set_tainted_by_errors();
+        }
+    }
+
+    pub fn write_field_index(&self, hir_id: hir::HirId, index: usize) {
+        self.typeck_results.borrow_mut().field_indices_mut().insert(hir_id, index);
+    }
+
+    pub(in super::super) fn write_resolution(
+        &self,
+        hir_id: hir::HirId,
+        r: Result<(DefKind, DefId), ErrorReported>,
+    ) {
+        self.typeck_results.borrow_mut().type_dependent_defs_mut().insert(hir_id, r);
+    }
+
+    pub fn write_method_call(&self, hir_id: hir::HirId, method: MethodCallee<'tcx>) {
+        debug!("write_method_call(hir_id={:?}, method={:?})", hir_id, method);
+        self.write_resolution(hir_id, Ok((DefKind::AssocFn, method.def_id)));
+        self.write_substs(hir_id, method.substs);
+
+        // When the method is confirmed, the `method.substs` includes
+        // parameters from not just the method, but also the impl of
+        // the method -- in particular, the `Self` type will be fully
+        // resolved. However, those are not something that the "user
+        // specified" -- i.e., those types come from the inferred type
+        // of the receiver, not something the user wrote. So when we
+        // create the user-substs, we want to replace those earlier
+        // types with just the types that the user actually wrote --
+        // that is, those that appear on the *method itself*.
+        //
+        // As an example, if the user wrote something like
+        // `foo.bar::<u32>(...)` -- the `Self` type here will be the
+        // type of `foo` (possibly adjusted), but we don't want to
+        // include that. We want just the `[_, u32]` part.
+        if !method.substs.is_noop() {
+            let method_generics = self.tcx.generics_of(method.def_id);
+            if !method_generics.params.is_empty() {
+                let user_type_annotation = self.infcx.probe(|_| {
+                    let user_substs = UserSubsts {
+                        substs: InternalSubsts::for_item(self.tcx, method.def_id, |param, _| {
+                            let i = param.index as usize;
+                            if i < method_generics.parent_count {
+                                self.infcx.var_for_def(DUMMY_SP, param)
+                            } else {
+                                method.substs[i]
+                            }
+                        }),
+                        user_self_ty: None, // not relevant here
+                    };
+
+                    self.infcx.canonicalize_user_type_annotation(&UserType::TypeOf(
+                        method.def_id,
+                        user_substs,
+                    ))
+                });
+
+                debug!("write_method_call: user_type_annotation={:?}", user_type_annotation);
+                self.write_user_type_annotation(hir_id, user_type_annotation);
+            }
+        }
+    }
+
+    pub fn write_substs(&self, node_id: hir::HirId, substs: SubstsRef<'tcx>) {
+        if !substs.is_noop() {
+            debug!("write_substs({:?}, {:?}) in fcx {}", node_id, substs, self.tag());
+
+            self.typeck_results.borrow_mut().node_substs_mut().insert(node_id, substs);
+        }
+    }
+
+    /// Given the substs that we just converted from the HIR, try to
+    /// canonicalize them and store them as user-given substitutions
+    /// (i.e., substitutions that must be respected by the NLL check).
+    ///
+    /// This should be invoked **before any unifications have
+    /// occurred**, so that annotations like `Vec<_>` are preserved
+    /// properly.
+    pub fn write_user_type_annotation_from_substs(
+        &self,
+        hir_id: hir::HirId,
+        def_id: DefId,
+        substs: SubstsRef<'tcx>,
+        user_self_ty: Option<UserSelfTy<'tcx>>,
+    ) {
+        debug!(
+            "write_user_type_annotation_from_substs: hir_id={:?} def_id={:?} substs={:?} \
+             user_self_ty={:?} in fcx {}",
+            hir_id,
+            def_id,
+            substs,
+            user_self_ty,
+            self.tag(),
+        );
+
+        if Self::can_contain_user_lifetime_bounds((substs, user_self_ty)) {
+            let canonicalized = self.infcx.canonicalize_user_type_annotation(&UserType::TypeOf(
+                def_id,
+                UserSubsts { substs, user_self_ty },
+            ));
+            debug!("write_user_type_annotation_from_substs: canonicalized={:?}", canonicalized);
+            self.write_user_type_annotation(hir_id, canonicalized);
+        }
+    }
+
+    pub fn write_user_type_annotation(
+        &self,
+        hir_id: hir::HirId,
+        canonical_user_type_annotation: CanonicalUserType<'tcx>,
+    ) {
+        debug!(
+            "write_user_type_annotation: hir_id={:?} canonical_user_type_annotation={:?} tag={}",
+            hir_id,
+            canonical_user_type_annotation,
+            self.tag(),
+        );
+
+        if !canonical_user_type_annotation.is_identity() {
+            self.typeck_results
+                .borrow_mut()
+                .user_provided_types_mut()
+                .insert(hir_id, canonical_user_type_annotation);
+        } else {
+            debug!("write_user_type_annotation: skipping identity substs");
+        }
+    }
+
+    pub fn apply_adjustments(&self, expr: &hir::Expr<'_>, adj: Vec<Adjustment<'tcx>>) {
+        debug!("apply_adjustments(expr={:?}, adj={:?})", expr, adj);
+
+        if adj.is_empty() {
+            return;
+        }
+
+        let autoborrow_mut = adj.iter().any(|adj| {
+            matches!(adj, &Adjustment {
+                kind: Adjust::Borrow(AutoBorrow::Ref(_, AutoBorrowMutability::Mut { .. })),
+                ..
+            })
+        });
+
+        match self.typeck_results.borrow_mut().adjustments_mut().entry(expr.hir_id) {
+            Entry::Vacant(entry) => {
+                entry.insert(adj);
+            }
+            Entry::Occupied(mut entry) => {
+                debug!(" - composing on top of {:?}", entry.get());
+                match (&entry.get()[..], &adj[..]) {
+                    // Applying any adjustment on top of a NeverToAny
+                    // is a valid NeverToAny adjustment, because it can't
+                    // be reached.
+                    (&[Adjustment { kind: Adjust::NeverToAny, .. }], _) => return,
+                    (&[
+                        Adjustment { kind: Adjust::Deref(_), .. },
+                        Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(..)), .. },
+                    ], &[
+                        Adjustment { kind: Adjust::Deref(_), .. },
+                        .. // Any following adjustments are allowed.
+                    ]) => {
+                        // A reborrow has no effect before a dereference.
+                    }
+                    // FIXME: currently we never try to compose autoderefs
+                    // and ReifyFnPointer/UnsafeFnPointer, but we could.
+                    _ =>
+                        bug!("while adjusting {:?}, can't compose {:?} and {:?}",
+                             expr, entry.get(), adj)
+                };
+                *entry.get_mut() = adj;
+            }
+        }
+
+        // If there is an mutable auto-borrow, it is equivalent to `&mut <expr>`.
+        // In this case implicit use of `Deref` and `Index` within `<expr>` should
+        // instead be `DerefMut` and `IndexMut`, so fix those up.
+        if autoborrow_mut {
+            self.convert_place_derefs_to_mutable(expr);
+        }
+    }
+
+    /// Basically whenever we are converting from a type scheme into
+    /// the fn body space, we always want to normalize associated
+    /// types as well. This function combines the two.
+    fn instantiate_type_scheme<T>(&self, span: Span, substs: SubstsRef<'tcx>, value: &T) -> T
+    where
+        T: TypeFoldable<'tcx>,
+    {
+        let value = value.subst(self.tcx, substs);
+        let result = self.normalize_associated_types_in(span, &value);
+        debug!("instantiate_type_scheme(value={:?}, substs={:?}) = {:?}", value, substs, result);
+        result
+    }
+
+    /// As `instantiate_type_scheme`, but for the bounds found in a
+    /// generic type scheme.
+    pub(in super::super) fn instantiate_bounds(
+        &self,
+        span: Span,
+        def_id: DefId,
+        substs: SubstsRef<'tcx>,
+    ) -> (ty::InstantiatedPredicates<'tcx>, Vec<Span>) {
+        let bounds = self.tcx.predicates_of(def_id);
+        let spans: Vec<Span> = bounds.predicates.iter().map(|(_, span)| *span).collect();
+        let result = bounds.instantiate(self.tcx, substs);
+        let result = self.normalize_associated_types_in(span, &result);
+        debug!(
+            "instantiate_bounds(bounds={:?}, substs={:?}) = {:?}, {:?}",
+            bounds, substs, result, spans,
+        );
+        (result, spans)
+    }
+
+    /// Replaces the opaque types from the given value with type variables,
+    /// and records the `OpaqueTypeMap` for later use during writeback. See
+    /// `InferCtxt::instantiate_opaque_types` for more details.
+    pub(in super::super) fn instantiate_opaque_types_from_value<T: TypeFoldable<'tcx>>(
+        &self,
+        parent_id: hir::HirId,
+        value: &T,
+        value_span: Span,
+    ) -> T {
+        let parent_def_id = self.tcx.hir().local_def_id(parent_id);
+        debug!(
+            "instantiate_opaque_types_from_value(parent_def_id={:?}, value={:?})",
+            parent_def_id, value
+        );
+
+        let (value, opaque_type_map) =
+            self.register_infer_ok_obligations(self.instantiate_opaque_types(
+                parent_def_id,
+                self.body_id,
+                self.param_env,
+                value,
+                value_span,
+            ));
+
+        let mut opaque_types = self.opaque_types.borrow_mut();
+        let mut opaque_types_vars = self.opaque_types_vars.borrow_mut();
+        for (ty, decl) in opaque_type_map {
+            let _ = opaque_types.insert(ty, decl);
+            let _ = opaque_types_vars.insert(decl.concrete_ty, decl.opaque_type);
+        }
+
+        value
+    }
+
+    pub(in super::super) fn normalize_associated_types_in<T>(&self, span: Span, value: &T) -> T
+    where
+        T: TypeFoldable<'tcx>,
+    {
+        self.inh.normalize_associated_types_in(span, self.body_id, self.param_env, value)
+    }
+
+    pub(in super::super) fn normalize_associated_types_in_as_infer_ok<T>(
+        &self,
+        span: Span,
+        value: &T,
+    ) -> InferOk<'tcx, T>
+    where
+        T: TypeFoldable<'tcx>,
+    {
+        self.inh.partially_normalize_associated_types_in(span, self.body_id, self.param_env, value)
+    }
+
+    pub fn require_type_meets(
+        &self,
+        ty: Ty<'tcx>,
+        span: Span,
+        code: traits::ObligationCauseCode<'tcx>,
+        def_id: DefId,
+    ) {
+        self.register_bound(ty, def_id, traits::ObligationCause::new(span, self.body_id, code));
+    }
+
+    pub fn require_type_is_sized(
+        &self,
+        ty: Ty<'tcx>,
+        span: Span,
+        code: traits::ObligationCauseCode<'tcx>,
+    ) {
+        if !ty.references_error() {
+            let lang_item = self.tcx.require_lang_item(LangItem::Sized, None);
+            self.require_type_meets(ty, span, code, lang_item);
+        }
+    }
+
+    pub fn require_type_is_sized_deferred(
+        &self,
+        ty: Ty<'tcx>,
+        span: Span,
+        code: traits::ObligationCauseCode<'tcx>,
+    ) {
+        if !ty.references_error() {
+            self.deferred_sized_obligations.borrow_mut().push((ty, span, code));
+        }
+    }
+
+    pub fn register_bound(
+        &self,
+        ty: Ty<'tcx>,
+        def_id: DefId,
+        cause: traits::ObligationCause<'tcx>,
+    ) {
+        if !ty.references_error() {
+            self.fulfillment_cx.borrow_mut().register_bound(
+                self,
+                self.param_env,
+                ty,
+                def_id,
+                cause,
+            );
+        }
+    }
+
+    pub fn to_ty(&self, ast_t: &hir::Ty<'_>) -> Ty<'tcx> {
+        let t = AstConv::ast_ty_to_ty(self, ast_t);
+        self.register_wf_obligation(t.into(), ast_t.span, traits::MiscObligation);
+        t
+    }
+
+    pub fn to_ty_saving_user_provided_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
+        let ty = self.to_ty(ast_ty);
+        debug!("to_ty_saving_user_provided_ty: ty={:?}", ty);
+
+        if Self::can_contain_user_lifetime_bounds(ty) {
+            let c_ty = self.infcx.canonicalize_response(&UserType::Ty(ty));
+            debug!("to_ty_saving_user_provided_ty: c_ty={:?}", c_ty);
+            self.typeck_results.borrow_mut().user_provided_types_mut().insert(ast_ty.hir_id, c_ty);
+        }
+
+        ty
+    }
+
+    pub fn to_const(&self, ast_c: &hir::AnonConst) -> &'tcx ty::Const<'tcx> {
+        let const_def_id = self.tcx.hir().local_def_id(ast_c.hir_id);
+        let c = ty::Const::from_anon_const(self.tcx, const_def_id);
+        self.register_wf_obligation(
+            c.into(),
+            self.tcx.hir().span(ast_c.hir_id),
+            ObligationCauseCode::MiscObligation,
+        );
+        c
+    }
+
+    pub fn const_arg_to_const(
+        &self,
+        ast_c: &hir::AnonConst,
+        param_def_id: DefId,
+    ) -> &'tcx ty::Const<'tcx> {
+        let const_def = ty::WithOptConstParam {
+            did: self.tcx.hir().local_def_id(ast_c.hir_id),
+            const_param_did: Some(param_def_id),
+        };
+        let c = ty::Const::from_opt_const_arg_anon_const(self.tcx, const_def);
+        self.register_wf_obligation(
+            c.into(),
+            self.tcx.hir().span(ast_c.hir_id),
+            ObligationCauseCode::MiscObligation,
+        );
+        c
+    }
+
+    // If the type given by the user has free regions, save it for later, since
+    // NLL would like to enforce those. Also pass in types that involve
+    // projections, since those can resolve to `'static` bounds (modulo #54940,
+    // which hopefully will be fixed by the time you see this comment, dear
+    // reader, although I have my doubts). Also pass in types with inference
+    // types, because they may be repeated. Other sorts of things are already
+    // sufficiently enforced with erased regions. =)
+    fn can_contain_user_lifetime_bounds<T>(t: T) -> bool
+    where
+        T: TypeFoldable<'tcx>,
+    {
+        t.has_free_regions() || t.has_projections() || t.has_infer_types()
+    }
+
+    pub fn node_ty(&self, id: hir::HirId) -> Ty<'tcx> {
+        match self.typeck_results.borrow().node_types().get(id) {
+            Some(&t) => t,
+            None if self.is_tainted_by_errors() => self.tcx.ty_error(),
+            None => {
+                bug!(
+                    "no type for node {}: {} in fcx {}",
+                    id,
+                    self.tcx.hir().node_to_string(id),
+                    self.tag()
+                );
+            }
+        }
+    }
+
+    /// Registers an obligation for checking later, during regionck, that `arg` is well-formed.
+    pub fn register_wf_obligation(
+        &self,
+        arg: subst::GenericArg<'tcx>,
+        span: Span,
+        code: traits::ObligationCauseCode<'tcx>,
+    ) {
+        // WF obligations never themselves fail, so no real need to give a detailed cause:
+        let cause = traits::ObligationCause::new(span, self.body_id, code);
+        self.register_predicate(traits::Obligation::new(
+            cause,
+            self.param_env,
+            ty::PredicateAtom::WellFormed(arg).to_predicate(self.tcx),
+        ));
+    }
+
+    /// Registers obligations that all `substs` are well-formed.
+    pub fn add_wf_bounds(&self, substs: SubstsRef<'tcx>, expr: &hir::Expr<'_>) {
+        for arg in substs.iter().filter(|arg| {
+            matches!(arg.unpack(), GenericArgKind::Type(..) | GenericArgKind::Const(..))
+        }) {
+            self.register_wf_obligation(arg, expr.span, traits::MiscObligation);
+        }
+    }
+
+    /// Given a fully substituted set of bounds (`generic_bounds`), and the values with which each
+    /// type/region parameter was instantiated (`substs`), creates and registers suitable
+    /// trait/region obligations.
+    ///
+    /// For example, if there is a function:
+    ///
+    /// ```
+    /// fn foo<'a,T:'a>(...)
+    /// ```
+    ///
+    /// and a reference:
+    ///
+    /// ```
+    /// let f = foo;
+    /// ```
+    ///
+    /// Then we will create a fresh region variable `'$0` and a fresh type variable `$1` for `'a`
+    /// and `T`. This routine will add a region obligation `$1:'$0` and register it locally.
+    pub fn add_obligations_for_parameters(
+        &self,
+        cause: traits::ObligationCause<'tcx>,
+        predicates: ty::InstantiatedPredicates<'tcx>,
+    ) {
+        assert!(!predicates.has_escaping_bound_vars());
+
+        debug!("add_obligations_for_parameters(predicates={:?})", predicates);
+
+        for obligation in traits::predicates_for_generics(cause, self.param_env, predicates) {
+            self.register_predicate(obligation);
+        }
+    }
+
+    // FIXME(arielb1): use this instead of field.ty everywhere
+    // Only for fields! Returns <none> for methods>
+    // Indifferent to privacy flags
+    pub fn field_ty(
+        &self,
+        span: Span,
+        field: &'tcx ty::FieldDef,
+        substs: SubstsRef<'tcx>,
+    ) -> Ty<'tcx> {
+        self.normalize_associated_types_in(span, &field.ty(self.tcx, substs))
+    }
+
+    pub(in super::super) fn resolve_generator_interiors(&self, def_id: DefId) {
+        let mut generators = self.deferred_generator_interiors.borrow_mut();
+        for (body_id, interior, kind) in generators.drain(..) {
+            self.select_obligations_where_possible(false, |_| {});
+            crate::check::generator_interior::resolve_interior(
+                self, def_id, body_id, interior, kind,
+            );
+        }
+    }
+
+    // Tries to apply a fallback to `ty` if it is an unsolved variable.
+    //
+    // - Unconstrained ints are replaced with `i32`.
+    //
+    // - Unconstrained floats are replaced with with `f64`.
+    //
+    // - Non-numerics get replaced with `!` when `#![feature(never_type_fallback)]`
+    //   is enabled. Otherwise, they are replaced with `()`.
+    //
+    // Fallback becomes very dubious if we have encountered type-checking errors.
+    // In that case, fallback to Error.
+    // The return value indicates whether fallback has occurred.
+    pub(in super::super) fn fallback_if_possible(&self, ty: Ty<'tcx>, mode: FallbackMode) -> bool {
+        use rustc_middle::ty::error::UnconstrainedNumeric::Neither;
+        use rustc_middle::ty::error::UnconstrainedNumeric::{UnconstrainedFloat, UnconstrainedInt};
+
+        assert!(ty.is_ty_infer());
+        let fallback = match self.type_is_unconstrained_numeric(ty) {
+            _ if self.is_tainted_by_errors() => self.tcx().ty_error(),
+            UnconstrainedInt => self.tcx.types.i32,
+            UnconstrainedFloat => self.tcx.types.f64,
+            Neither if self.type_var_diverges(ty) => self.tcx.mk_diverging_default(),
+            Neither => {
+                // This type variable was created from the instantiation of an opaque
+                // type. The fact that we're attempting to perform fallback for it
+                // means that the function neither constrained it to a concrete
+                // type, nor to the opaque type itself.
+                //
+                // For example, in this code:
+                //
+                //```
+                // type MyType = impl Copy;
+                // fn defining_use() -> MyType { true }
+                // fn other_use() -> MyType { defining_use() }
+                // ```
+                //
+                // `defining_use` will constrain the instantiated inference
+                // variable to `bool`, while `other_use` will constrain
+                // the instantiated inference variable to `MyType`.
+                //
+                // When we process opaque types during writeback, we
+                // will handle cases like `other_use`, and not count
+                // them as defining usages
+                //
+                // However, we also need to handle cases like this:
+                //
+                // ```rust
+                // pub type Foo = impl Copy;
+                // fn produce() -> Option<Foo> {
+                //     None
+                //  }
+                //  ```
+                //
+                // In the above snippet, the inference variable created by
+                // instantiating `Option<Foo>` will be completely unconstrained.
+                // We treat this as a non-defining use by making the inference
+                // variable fall back to the opaque type itself.
+                if let FallbackMode::All = mode {
+                    if let Some(opaque_ty) = self.opaque_types_vars.borrow().get(ty) {
+                        debug!(
+                            "fallback_if_possible: falling back opaque type var {:?} to {:?}",
+                            ty, opaque_ty
+                        );
+                        *opaque_ty
+                    } else {
+                        return false;
+                    }
+                } else {
+                    return false;
+                }
+            }
+        };
+        debug!("fallback_if_possible: defaulting `{:?}` to `{:?}`", ty, fallback);
+        self.demand_eqtype(rustc_span::DUMMY_SP, ty, fallback);
+        true
+    }
+
+    pub(in super::super) fn select_all_obligations_or_error(&self) {
+        debug!("select_all_obligations_or_error");
+        if let Err(errors) = self.fulfillment_cx.borrow_mut().select_all_or_error(&self) {
+            self.report_fulfillment_errors(&errors, self.inh.body_id, false);
+        }
+    }
+
+    /// Select as many obligations as we can at present.
+    pub(in super::super) fn select_obligations_where_possible(
+        &self,
+        fallback_has_occurred: bool,
+        mutate_fullfillment_errors: impl Fn(&mut Vec<traits::FulfillmentError<'tcx>>),
+    ) {
+        let result = self.fulfillment_cx.borrow_mut().select_where_possible(self);
+        if let Err(mut errors) = result {
+            mutate_fullfillment_errors(&mut errors);
+            self.report_fulfillment_errors(&errors, self.inh.body_id, fallback_has_occurred);
+        }
+    }
+
+    /// For the overloaded place expressions (`*x`, `x[3]`), the trait
+    /// returns a type of `&T`, but the actual type we assign to the
+    /// *expression* is `T`. So this function just peels off the return
+    /// type by one layer to yield `T`.
+    pub(in super::super) fn make_overloaded_place_return_type(
+        &self,
+        method: MethodCallee<'tcx>,
+    ) -> ty::TypeAndMut<'tcx> {
+        // extract method return type, which will be &T;
+        let ret_ty = method.sig.output();
+
+        // method returns &T, but the type as visible to user is T, so deref
+        ret_ty.builtin_deref(true).unwrap()
+    }
+
+    fn self_type_matches_expected_vid(
+        &self,
+        trait_ref: ty::PolyTraitRef<'tcx>,
+        expected_vid: ty::TyVid,
+    ) -> bool {
+        let self_ty = self.shallow_resolve(trait_ref.skip_binder().self_ty());
+        debug!(
+            "self_type_matches_expected_vid(trait_ref={:?}, self_ty={:?}, expected_vid={:?})",
+            trait_ref, self_ty, expected_vid
+        );
+        match *self_ty.kind() {
+            ty::Infer(ty::TyVar(found_vid)) => {
+                // FIXME: consider using `sub_root_var` here so we
+                // can see through subtyping.
+                let found_vid = self.root_var(found_vid);
+                debug!("self_type_matches_expected_vid - found_vid={:?}", found_vid);
+                expected_vid == found_vid
+            }
+            _ => false,
+        }
+    }
+
+    pub(in super::super) fn obligations_for_self_ty<'b>(
+        &'b self,
+        self_ty: ty::TyVid,
+    ) -> impl Iterator<Item = (ty::PolyTraitRef<'tcx>, traits::PredicateObligation<'tcx>)>
+    + Captures<'tcx>
+    + 'b {
+        // FIXME: consider using `sub_root_var` here so we
+        // can see through subtyping.
+        let ty_var_root = self.root_var(self_ty);
+        debug!(
+            "obligations_for_self_ty: self_ty={:?} ty_var_root={:?} pending_obligations={:?}",
+            self_ty,
+            ty_var_root,
+            self.fulfillment_cx.borrow().pending_obligations()
+        );
+
+        self.fulfillment_cx
+            .borrow()
+            .pending_obligations()
+            .into_iter()
+            .filter_map(move |obligation| {
+                match obligation.predicate.skip_binders() {
+                    ty::PredicateAtom::Projection(data) => {
+                        Some((ty::Binder::bind(data).to_poly_trait_ref(self.tcx), obligation))
+                    }
+                    ty::PredicateAtom::Trait(data, _) => {
+                        Some((ty::Binder::bind(data).to_poly_trait_ref(), obligation))
+                    }
+                    ty::PredicateAtom::Subtype(..) => None,
+                    ty::PredicateAtom::RegionOutlives(..) => None,
+                    ty::PredicateAtom::TypeOutlives(..) => None,
+                    ty::PredicateAtom::WellFormed(..) => None,
+                    ty::PredicateAtom::ObjectSafe(..) => None,
+                    ty::PredicateAtom::ConstEvaluatable(..) => None,
+                    ty::PredicateAtom::ConstEquate(..) => None,
+                    // N.B., this predicate is created by breaking down a
+                    // `ClosureType: FnFoo()` predicate, where
+                    // `ClosureType` represents some `Closure`. It can't
+                    // possibly be referring to the current closure,
+                    // because we haven't produced the `Closure` for
+                    // this closure yet; this is exactly why the other
+                    // code is looking for a self type of a unresolved
+                    // inference variable.
+                    ty::PredicateAtom::ClosureKind(..) => None,
+                    ty::PredicateAtom::TypeWellFormedFromEnv(..) => None,
+                }
+            })
+            .filter(move |(tr, _)| self.self_type_matches_expected_vid(*tr, ty_var_root))
+    }
+
+    pub(in super::super) fn type_var_is_sized(&self, self_ty: ty::TyVid) -> bool {
+        self.obligations_for_self_ty(self_ty)
+            .any(|(tr, _)| Some(tr.def_id()) == self.tcx.lang_items().sized_trait())
+    }
+
+    pub(in super::super) fn err_args(&self, len: usize) -> Vec<Ty<'tcx>> {
+        vec![self.tcx.ty_error(); len]
+    }
+
+    /// Unifies the output type with the expected type early, for more coercions
+    /// and forward type information on the input expressions.
+    pub(in super::super) fn expected_inputs_for_expected_output(
+        &self,
+        call_span: Span,
+        expected_ret: Expectation<'tcx>,
+        formal_ret: Ty<'tcx>,
+        formal_args: &[Ty<'tcx>],
+    ) -> Vec<Ty<'tcx>> {
+        let formal_ret = self.resolve_vars_with_obligations(formal_ret);
+        let ret_ty = match expected_ret.only_has_type(self) {
+            Some(ret) => ret,
+            None => return Vec::new(),
+        };
+        let expect_args = self
+            .fudge_inference_if_ok(|| {
+                // Attempt to apply a subtyping relationship between the formal
+                // return type (likely containing type variables if the function
+                // is polymorphic) and the expected return type.
+                // No argument expectations are produced if unification fails.
+                let origin = self.misc(call_span);
+                let ures = self.at(&origin, self.param_env).sup(ret_ty, &formal_ret);
+
+                // FIXME(#27336) can't use ? here, Try::from_error doesn't default
+                // to identity so the resulting type is not constrained.
+                match ures {
+                    Ok(ok) => {
+                        // Process any obligations locally as much as
+                        // we can.  We don't care if some things turn
+                        // out unconstrained or ambiguous, as we're
+                        // just trying to get hints here.
+                        self.save_and_restore_in_snapshot_flag(|_| {
+                            let mut fulfill = TraitEngine::new(self.tcx);
+                            for obligation in ok.obligations {
+                                fulfill.register_predicate_obligation(self, obligation);
+                            }
+                            fulfill.select_where_possible(self)
+                        })
+                        .map_err(|_| ())?;
+                    }
+                    Err(_) => return Err(()),
+                }
+
+                // Record all the argument types, with the substitutions
+                // produced from the above subtyping unification.
+                Ok(formal_args.iter().map(|ty| self.resolve_vars_if_possible(ty)).collect())
+            })
+            .unwrap_or_default();
+        debug!(
+            "expected_inputs_for_expected_output(formal={:?} -> {:?}, expected={:?} -> {:?})",
+            formal_args, formal_ret, expect_args, expected_ret
+        );
+        expect_args
+    }
+
+    pub(in super::super) fn resolve_lang_item_path(
+        &self,
+        lang_item: hir::LangItem,
+        span: Span,
+        hir_id: hir::HirId,
+    ) -> (Res, Ty<'tcx>) {
+        let def_id = self.tcx.require_lang_item(lang_item, Some(span));
+        let def_kind = self.tcx.def_kind(def_id);
+
+        let item_ty = if let DefKind::Variant = def_kind {
+            self.tcx.type_of(self.tcx.parent(def_id).expect("variant w/out parent"))
+        } else {
+            self.tcx.type_of(def_id)
+        };
+        let substs = self.infcx.fresh_substs_for_item(span, def_id);
+        let ty = item_ty.subst(self.tcx, substs);
+
+        self.write_resolution(hir_id, Ok((def_kind, def_id)));
+        self.add_required_obligations(span, def_id, &substs);
+        (Res::Def(def_kind, def_id), ty)
+    }
+
+    /// Resolves an associated value path into a base type and associated constant, or method
+    /// resolution. The newly resolved definition is written into `type_dependent_defs`.
+    pub fn resolve_ty_and_res_ufcs<'b>(
+        &self,
+        qpath: &'b QPath<'b>,
+        hir_id: hir::HirId,
+        span: Span,
+    ) -> (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]) {
+        debug!("resolve_ty_and_res_ufcs: qpath={:?} hir_id={:?} span={:?}", qpath, hir_id, span);
+        let (ty, qself, item_segment) = match *qpath {
+            QPath::Resolved(ref opt_qself, ref path) => {
+                return (
+                    path.res,
+                    opt_qself.as_ref().map(|qself| self.to_ty(qself)),
+                    &path.segments[..],
+                );
+            }
+            QPath::TypeRelative(ref qself, ref segment) => (self.to_ty(qself), qself, segment),
+            QPath::LangItem(..) => bug!("`resolve_ty_and_res_ufcs` called on `LangItem`"),
+        };
+        if let Some(&cached_result) = self.typeck_results.borrow().type_dependent_defs().get(hir_id)
+        {
+            // Return directly on cache hit. This is useful to avoid doubly reporting
+            // errors with default match binding modes. See #44614.
+            let def =
+                cached_result.map(|(kind, def_id)| Res::Def(kind, def_id)).unwrap_or(Res::Err);
+            return (def, Some(ty), slice::from_ref(&**item_segment));
+        }
+        let item_name = item_segment.ident;
+        let result = self.resolve_ufcs(span, item_name, ty, hir_id).or_else(|error| {
+            let result = match error {
+                method::MethodError::PrivateMatch(kind, def_id, _) => Ok((kind, def_id)),
+                _ => Err(ErrorReported),
+            };
+            if item_name.name != kw::Invalid {
+                if let Some(mut e) = self.report_method_error(
+                    span,
+                    ty,
+                    item_name,
+                    SelfSource::QPath(qself),
+                    error,
+                    None,
+                ) {
+                    e.emit();
+                }
+            }
+            result
+        });
+
+        // Write back the new resolution.
+        self.write_resolution(hir_id, result);
+        (
+            result.map(|(kind, def_id)| Res::Def(kind, def_id)).unwrap_or(Res::Err),
+            Some(ty),
+            slice::from_ref(&**item_segment),
+        )
+    }
+
+    /// Given a function `Node`, return its `FnDecl` if it exists, or `None` otherwise.
+    pub(in super::super) fn get_node_fn_decl(
+        &self,
+        node: Node<'tcx>,
+    ) -> Option<(&'tcx hir::FnDecl<'tcx>, Ident, bool)> {
+        match node {
+            Node::Item(&hir::Item { ident, kind: hir::ItemKind::Fn(ref sig, ..), .. }) => {
+                // This is less than ideal, it will not suggest a return type span on any
+                // method called `main`, regardless of whether it is actually the entry point,
+                // but it will still present it as the reason for the expected type.
+                Some((&sig.decl, ident, ident.name != sym::main))
+            }
+            Node::TraitItem(&hir::TraitItem {
+                ident,
+                kind: hir::TraitItemKind::Fn(ref sig, ..),
+                ..
+            }) => Some((&sig.decl, ident, true)),
+            Node::ImplItem(&hir::ImplItem {
+                ident,
+                kind: hir::ImplItemKind::Fn(ref sig, ..),
+                ..
+            }) => Some((&sig.decl, ident, false)),
+            _ => None,
+        }
+    }
+
+    /// Given a `HirId`, return the `FnDecl` of the method it is enclosed by and whether a
+    /// suggestion can be made, `None` otherwise.
+    pub fn get_fn_decl(&self, blk_id: hir::HirId) -> Option<(&'tcx hir::FnDecl<'tcx>, bool)> {
+        // Get enclosing Fn, if it is a function or a trait method, unless there's a `loop` or
+        // `while` before reaching it, as block tail returns are not available in them.
+        self.tcx.hir().get_return_block(blk_id).and_then(|blk_id| {
+            let parent = self.tcx.hir().get(blk_id);
+            self.get_node_fn_decl(parent).map(|(fn_decl, _, is_main)| (fn_decl, is_main))
+        })
+    }
+
+    pub(in super::super) fn note_internal_mutation_in_method(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        expr: &hir::Expr<'_>,
+        expected: Ty<'tcx>,
+        found: Ty<'tcx>,
+    ) {
+        if found != self.tcx.types.unit {
+            return;
+        }
+        if let ExprKind::MethodCall(path_segment, _, [rcvr, ..], _) = expr.kind {
+            if self
+                .typeck_results
+                .borrow()
+                .expr_ty_adjusted_opt(rcvr)
+                .map_or(true, |ty| expected.peel_refs() != ty.peel_refs())
+            {
+                return;
+            }
+            let mut sp = MultiSpan::from_span(path_segment.ident.span);
+            sp.push_span_label(
+                path_segment.ident.span,
+                format!(
+                    "this call modifies {} in-place",
+                    match rcvr.kind {
+                        ExprKind::Path(QPath::Resolved(
+                            None,
+                            hir::Path { segments: [segment], .. },
+                        )) => format!("`{}`", segment.ident),
+                        _ => "its receiver".to_string(),
+                    }
+                ),
+            );
+            sp.push_span_label(
+                rcvr.span,
+                "you probably want to use this value after calling the method...".to_string(),
+            );
+            err.span_note(
+                sp,
+                &format!("method `{}` modifies its receiver in-place", path_segment.ident),
+            );
+            err.note(&format!("...instead of the `()` output of method `{}`", path_segment.ident));
+        }
+    }
+
+    pub(in super::super) fn note_need_for_fn_pointer(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        expected: Ty<'tcx>,
+        found: Ty<'tcx>,
+    ) {
+        let (sig, did, substs) = match (&expected.kind(), &found.kind()) {
+            (ty::FnDef(did1, substs1), ty::FnDef(did2, substs2)) => {
+                let sig1 = self.tcx.fn_sig(*did1).subst(self.tcx, substs1);
+                let sig2 = self.tcx.fn_sig(*did2).subst(self.tcx, substs2);
+                if sig1 != sig2 {
+                    return;
+                }
+                err.note(
+                    "different `fn` items always have unique types, even if their signatures are \
+                     the same",
+                );
+                (sig1, *did1, substs1)
+            }
+            (ty::FnDef(did, substs), ty::FnPtr(sig2)) => {
+                let sig1 = self.tcx.fn_sig(*did).subst(self.tcx, substs);
+                if sig1 != *sig2 {
+                    return;
+                }
+                (sig1, *did, substs)
+            }
+            _ => return,
+        };
+        err.help(&format!("change the expected type to be function pointer `{}`", sig));
+        err.help(&format!(
+            "if the expected type is due to type inference, cast the expected `fn` to a function \
+             pointer: `{} as {}`",
+            self.tcx.def_path_str_with_substs(did, substs),
+            sig
+        ));
+    }
+
+    pub(in super::super) fn could_remove_semicolon(
+        &self,
+        blk: &'tcx hir::Block<'tcx>,
+        expected_ty: Ty<'tcx>,
+    ) -> Option<Span> {
+        // Be helpful when the user wrote `{... expr;}` and
+        // taking the `;` off is enough to fix the error.
+        let last_stmt = blk.stmts.last()?;
+        let last_expr = match last_stmt.kind {
+            hir::StmtKind::Semi(ref e) => e,
+            _ => return None,
+        };
+        let last_expr_ty = self.node_ty(last_expr.hir_id);
+        if matches!(last_expr_ty.kind(), ty::Error(_))
+            || self.can_sub(self.param_env, last_expr_ty, expected_ty).is_err()
+        {
+            return None;
+        }
+        let original_span = original_sp(last_stmt.span, blk.span);
+        Some(original_span.with_lo(original_span.hi() - BytePos(1)))
+    }
+
+    // Instantiates the given path, which must refer to an item with the given
+    // number of type parameters and type.
+    pub fn instantiate_value_path(
+        &self,
+        segments: &[hir::PathSegment<'_>],
+        self_ty: Option<Ty<'tcx>>,
+        res: Res,
+        span: Span,
+        hir_id: hir::HirId,
+    ) -> (Ty<'tcx>, Res) {
+        debug!(
+            "instantiate_value_path(segments={:?}, self_ty={:?}, res={:?}, hir_id={})",
+            segments, self_ty, res, hir_id,
+        );
+
+        let tcx = self.tcx;
+
+        let path_segs = match res {
+            Res::Local(_) | Res::SelfCtor(_) => vec![],
+            Res::Def(kind, def_id) => {
+                AstConv::def_ids_for_value_path_segments(self, segments, self_ty, kind, def_id)
+            }
+            _ => bug!("instantiate_value_path on {:?}", res),
+        };
+
+        let mut user_self_ty = None;
+        let mut is_alias_variant_ctor = false;
+        match res {
+            Res::Def(DefKind::Ctor(CtorOf::Variant, _), _) => {
+                if let Some(self_ty) = self_ty {
+                    let adt_def = self_ty.ty_adt_def().unwrap();
+                    user_self_ty = Some(UserSelfTy { impl_def_id: adt_def.did, self_ty });
+                    is_alias_variant_ctor = true;
+                }
+            }
+            Res::Def(DefKind::AssocFn | DefKind::AssocConst, def_id) => {
+                let container = tcx.associated_item(def_id).container;
+                debug!("instantiate_value_path: def_id={:?} container={:?}", def_id, container);
+                match container {
+                    ty::TraitContainer(trait_did) => {
+                        callee::check_legal_trait_for_method_call(tcx, span, None, trait_did)
+                    }
+                    ty::ImplContainer(impl_def_id) => {
+                        if segments.len() == 1 {
+                            // `<T>::assoc` will end up here, and so
+                            // can `T::assoc`. It this came from an
+                            // inherent impl, we need to record the
+                            // `T` for posterity (see `UserSelfTy` for
+                            // details).
+                            let self_ty = self_ty.expect("UFCS sugared assoc missing Self");
+                            user_self_ty = Some(UserSelfTy { impl_def_id, self_ty });
+                        }
+                    }
+                }
+            }
+            _ => {}
+        }
+
+        // Now that we have categorized what space the parameters for each
+        // segment belong to, let's sort out the parameters that the user
+        // provided (if any) into their appropriate spaces. We'll also report
+        // errors if type parameters are provided in an inappropriate place.
+
+        let generic_segs: FxHashSet<_> = path_segs.iter().map(|PathSeg(_, index)| index).collect();
+        let generics_has_err = AstConv::prohibit_generics(
+            self,
+            segments.iter().enumerate().filter_map(|(index, seg)| {
+                if !generic_segs.contains(&index) || is_alias_variant_ctor {
+                    Some(seg)
+                } else {
+                    None
+                }
+            }),
+        );
+
+        if let Res::Local(hid) = res {
+            let ty = self.local_ty(span, hid).decl_ty;
+            let ty = self.normalize_associated_types_in(span, &ty);
+            self.write_ty(hir_id, ty);
+            return (ty, res);
+        }
+
+        if generics_has_err {
+            // Don't try to infer type parameters when prohibited generic arguments were given.
+            user_self_ty = None;
+        }
+
+        // Now we have to compare the types that the user *actually*
+        // provided against the types that were *expected*. If the user
+        // did not provide any types, then we want to substitute inference
+        // variables. If the user provided some types, we may still need
+        // to add defaults. If the user provided *too many* types, that's
+        // a problem.
+
+        let mut infer_args_for_err = FxHashSet::default();
+        for &PathSeg(def_id, index) in &path_segs {
+            let seg = &segments[index];
+            let generics = tcx.generics_of(def_id);
+            // Argument-position `impl Trait` is treated as a normal generic
+            // parameter internally, but we don't allow users to specify the
+            // parameter's value explicitly, so we have to do some error-
+            // checking here.
+            if let GenericArgCountResult {
+                correct: Err(GenericArgCountMismatch { reported: Some(ErrorReported), .. }),
+                ..
+            } = AstConv::check_generic_arg_count_for_call(
+                tcx, span, &generics, &seg, false, // `is_method_call`
+            ) {
+                infer_args_for_err.insert(index);
+                self.set_tainted_by_errors(); // See issue #53251.
+            }
+        }
+
+        let has_self = path_segs
+            .last()
+            .map(|PathSeg(def_id, _)| tcx.generics_of(*def_id).has_self)
+            .unwrap_or(false);
+
+        let (res, self_ctor_substs) = if let Res::SelfCtor(impl_def_id) = res {
+            let ty = self.normalize_ty(span, tcx.at(span).type_of(impl_def_id));
+            match *ty.kind() {
+                ty::Adt(adt_def, substs) if adt_def.has_ctor() => {
+                    let variant = adt_def.non_enum_variant();
+                    let ctor_def_id = variant.ctor_def_id.unwrap();
+                    (
+                        Res::Def(DefKind::Ctor(CtorOf::Struct, variant.ctor_kind), ctor_def_id),
+                        Some(substs),
+                    )
+                }
+                _ => {
+                    let mut err = tcx.sess.struct_span_err(
+                        span,
+                        "the `Self` constructor can only be used with tuple or unit structs",
+                    );
+                    if let Some(adt_def) = ty.ty_adt_def() {
+                        match adt_def.adt_kind() {
+                            AdtKind::Enum => {
+                                err.help("did you mean to use one of the enum's variants?");
+                            }
+                            AdtKind::Struct | AdtKind::Union => {
+                                err.span_suggestion(
+                                    span,
+                                    "use curly brackets",
+                                    String::from("Self { /* fields */ }"),
+                                    Applicability::HasPlaceholders,
+                                );
+                            }
+                        }
+                    }
+                    err.emit();
+
+                    return (tcx.ty_error(), res);
+                }
+            }
+        } else {
+            (res, None)
+        };
+        let def_id = res.def_id();
+
+        // The things we are substituting into the type should not contain
+        // escaping late-bound regions, and nor should the base type scheme.
+        let ty = tcx.type_of(def_id);
+
+        let arg_count = GenericArgCountResult {
+            explicit_late_bound: ExplicitLateBound::No,
+            correct: if infer_args_for_err.is_empty() {
+                Ok(())
+            } else {
+                Err(GenericArgCountMismatch::default())
+            },
+        };
+
+        let substs = self_ctor_substs.unwrap_or_else(|| {
+            AstConv::create_substs_for_generic_args(
+                tcx,
+                def_id,
+                &[][..],
+                has_self,
+                self_ty,
+                arg_count,
+                // Provide the generic args, and whether types should be inferred.
+                |def_id| {
+                    if let Some(&PathSeg(_, index)) =
+                        path_segs.iter().find(|&PathSeg(did, _)| *did == def_id)
+                    {
+                        // If we've encountered an `impl Trait`-related error, we're just
+                        // going to infer the arguments for better error messages.
+                        if !infer_args_for_err.contains(&index) {
+                            // Check whether the user has provided generic arguments.
+                            if let Some(ref data) = segments[index].args {
+                                return (Some(data), segments[index].infer_args);
+                            }
+                        }
+                        return (None, segments[index].infer_args);
+                    }
+
+                    (None, true)
+                },
+                // Provide substitutions for parameters for which (valid) arguments have been provided.
+                |param, arg| match (&param.kind, arg) {
+                    (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
+                        AstConv::ast_region_to_region(self, lt, Some(param)).into()
+                    }
+                    (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
+                        self.to_ty(ty).into()
+                    }
+                    (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
+                        self.const_arg_to_const(&ct.value, param.def_id).into()
+                    }
+                    _ => unreachable!(),
+                },
+                // Provide substitutions for parameters for which arguments are inferred.
+                |substs, param, infer_args| {
+                    match param.kind {
+                        GenericParamDefKind::Lifetime => {
+                            self.re_infer(Some(param), span).unwrap().into()
+                        }
+                        GenericParamDefKind::Type { has_default, .. } => {
+                            if !infer_args && has_default {
+                                // If we have a default, then we it doesn't matter that we're not
+                                // inferring the type arguments: we provide the default where any
+                                // is missing.
+                                let default = tcx.type_of(param.def_id);
+                                self.normalize_ty(
+                                    span,
+                                    default.subst_spanned(tcx, substs.unwrap(), Some(span)),
+                                )
+                                .into()
+                            } else {
+                                // If no type arguments were provided, we have to infer them.
+                                // This case also occurs as a result of some malformed input, e.g.
+                                // a lifetime argument being given instead of a type parameter.
+                                // Using inference instead of `Error` gives better error messages.
+                                self.var_for_def(span, param)
+                            }
+                        }
+                        GenericParamDefKind::Const => {
+                            // FIXME(const_generics:defaults)
+                            // No const parameters were provided, we have to infer them.
+                            self.var_for_def(span, param)
+                        }
+                    }
+                },
+            )
+        });
+        assert!(!substs.has_escaping_bound_vars());
+        assert!(!ty.has_escaping_bound_vars());
+
+        // First, store the "user substs" for later.
+        self.write_user_type_annotation_from_substs(hir_id, def_id, substs, user_self_ty);
+
+        self.add_required_obligations(span, def_id, &substs);
+
+        // Substitute the values for the type parameters into the type of
+        // the referenced item.
+        let ty_substituted = self.instantiate_type_scheme(span, &substs, &ty);
+
+        if let Some(UserSelfTy { impl_def_id, self_ty }) = user_self_ty {
+            // In the case of `Foo<T>::method` and `<Foo<T>>::method`, if `method`
+            // is inherent, there is no `Self` parameter; instead, the impl needs
+            // type parameters, which we can infer by unifying the provided `Self`
+            // with the substituted impl type.
+            // This also occurs for an enum variant on a type alias.
+            let ty = tcx.type_of(impl_def_id);
+
+            let impl_ty = self.instantiate_type_scheme(span, &substs, &ty);
+            match self.at(&self.misc(span), self.param_env).sup(impl_ty, self_ty) {
+                Ok(ok) => self.register_infer_ok_obligations(ok),
+                Err(_) => {
+                    self.tcx.sess.delay_span_bug(
+                        span,
+                        &format!(
+                        "instantiate_value_path: (UFCS) {:?} was a subtype of {:?} but now is not?",
+                        self_ty,
+                        impl_ty,
+                    ),
+                    );
+                }
+            }
+        }
+
+        self.check_rustc_args_require_const(def_id, hir_id, span);
+
+        debug!("instantiate_value_path: type of {:?} is {:?}", hir_id, ty_substituted);
+        self.write_substs(hir_id, substs);
+
+        (ty_substituted, res)
+    }
+
+    /// Add all the obligations that are required, substituting and normalized appropriately.
+    fn add_required_obligations(&self, span: Span, def_id: DefId, substs: &SubstsRef<'tcx>) {
+        let (bounds, spans) = self.instantiate_bounds(span, def_id, &substs);
+
+        for (i, mut obligation) in traits::predicates_for_generics(
+            traits::ObligationCause::new(span, self.body_id, traits::ItemObligation(def_id)),
+            self.param_env,
+            bounds,
+        )
+        .enumerate()
+        {
+            // This makes the error point at the bound, but we want to point at the argument
+            if let Some(span) = spans.get(i) {
+                obligation.cause.make_mut().code = traits::BindingObligation(def_id, *span);
+            }
+            self.register_predicate(obligation);
+        }
+    }
+
+    /// Resolves `typ` by a single level if `typ` is a type variable.
+    /// If no resolution is possible, then an error is reported.
+    /// Numeric inference variables may be left unresolved.
+    pub fn structurally_resolved_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
+        let ty = self.resolve_vars_with_obligations(ty);
+        if !ty.is_ty_var() {
+            ty
+        } else {
+            if !self.is_tainted_by_errors() {
+                self.emit_inference_failure_err((**self).body_id, sp, ty.into(), E0282)
+                    .note("type must be known at this point")
+                    .emit();
+            }
+            let err = self.tcx.ty_error();
+            self.demand_suptype(sp, err, ty);
+            err
+        }
+    }
+
+    pub(in super::super) fn with_breakable_ctxt<F: FnOnce() -> R, R>(
+        &self,
+        id: hir::HirId,
+        ctxt: BreakableCtxt<'tcx>,
+        f: F,
+    ) -> (BreakableCtxt<'tcx>, R) {
+        let index;
+        {
+            let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
+            index = enclosing_breakables.stack.len();
+            enclosing_breakables.by_id.insert(id, index);
+            enclosing_breakables.stack.push(ctxt);
+        }
+        let result = f();
+        let ctxt = {
+            let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
+            debug_assert!(enclosing_breakables.stack.len() == index + 1);
+            enclosing_breakables.by_id.remove(&id).expect("missing breakable context");
+            enclosing_breakables.stack.pop().expect("missing breakable context")
+        };
+        (ctxt, result)
+    }
+
+    /// Instantiate a QueryResponse in a probe context, without a
+    /// good ObligationCause.
+    pub(in super::super) fn probe_instantiate_query_response(
+        &self,
+        span: Span,
+        original_values: &OriginalQueryValues<'tcx>,
+        query_result: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>,
+    ) -> InferResult<'tcx, Ty<'tcx>> {
+        self.instantiate_query_response_and_region_obligations(
+            &traits::ObligationCause::misc(span, self.body_id),
+            self.param_env,
+            original_values,
+            query_result,
+        )
+    }
+
+    /// Returns `true` if an expression is contained inside the LHS of an assignment expression.
+    pub(in super::super) fn expr_in_place(&self, mut expr_id: hir::HirId) -> bool {
+        let mut contained_in_place = false;
+
+        while let hir::Node::Expr(parent_expr) =
+            self.tcx.hir().get(self.tcx.hir().get_parent_node(expr_id))
+        {
+            match &parent_expr.kind {
+                hir::ExprKind::Assign(lhs, ..) | hir::ExprKind::AssignOp(_, lhs, ..) => {
+                    if lhs.hir_id == expr_id {
+                        contained_in_place = true;
+                        break;
+                    }
+                }
+                _ => (),
+            }
+            expr_id = parent_expr.hir_id;
+        }
+
+        contained_in_place
+    }
+}
diff --git a/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs b/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs
new file mode 100644
index 00000000000..3224e04ee49
--- /dev/null
+++ b/compiler/rustc_typeck/src/check/fn_ctxt/checks.rs
@@ -0,0 +1,979 @@
+use crate::astconv::AstConv;
+use crate::check::coercion::CoerceMany;
+use crate::check::method::MethodCallee;
+use crate::check::Expectation::*;
+use crate::check::TupleArgumentsFlag::*;
+use crate::check::{
+    potentially_plural_count, struct_span_err, BreakableCtxt, Diverges, Expectation, FnCtxt,
+    LocalTy, Needs, TupleArgumentsFlag,
+};
+
+use rustc_ast as ast;
+use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticId};
+use rustc_hir as hir;
+use rustc_hir::def::{DefKind, Res};
+use rustc_hir::def_id::DefId;
+use rustc_hir::{ExprKind, Node, QPath};
+use rustc_middle::ty::adjustment::AllowTwoPhase;
+use rustc_middle::ty::fold::TypeFoldable;
+use rustc_middle::ty::{self, Ty};
+use rustc_session::Session;
+use rustc_span::symbol::{sym, Ident};
+use rustc_span::{self, Span};
+use rustc_trait_selection::traits::{self, ObligationCauseCode};
+
+use std::mem::replace;
+use std::slice;
+
+impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
+    pub(in super::super) fn check_casts(&self) {
+        let mut deferred_cast_checks = self.deferred_cast_checks.borrow_mut();
+        for cast in deferred_cast_checks.drain(..) {
+            cast.check(self);
+        }
+    }
+
+    pub(in super::super) fn check_method_argument_types(
+        &self,
+        sp: Span,
+        expr: &'tcx hir::Expr<'tcx>,
+        method: Result<MethodCallee<'tcx>, ()>,
+        args_no_rcvr: &'tcx [hir::Expr<'tcx>],
+        tuple_arguments: TupleArgumentsFlag,
+        expected: Expectation<'tcx>,
+    ) -> Ty<'tcx> {
+        let has_error = match method {
+            Ok(method) => method.substs.references_error() || method.sig.references_error(),
+            Err(_) => true,
+        };
+        if has_error {
+            let err_inputs = self.err_args(args_no_rcvr.len());
+
+            let err_inputs = match tuple_arguments {
+                DontTupleArguments => err_inputs,
+                TupleArguments => vec![self.tcx.intern_tup(&err_inputs[..])],
+            };
+
+            self.check_argument_types(
+                sp,
+                expr,
+                &err_inputs[..],
+                &[],
+                args_no_rcvr,
+                false,
+                tuple_arguments,
+                None,
+            );
+            return self.tcx.ty_error();
+        }
+
+        let method = method.unwrap();
+        // HACK(eddyb) ignore self in the definition (see above).
+        let expected_arg_tys = self.expected_inputs_for_expected_output(
+            sp,
+            expected,
+            method.sig.output(),
+            &method.sig.inputs()[1..],
+        );
+        self.check_argument_types(
+            sp,
+            expr,
+            &method.sig.inputs()[1..],
+            &expected_arg_tys[..],
+            args_no_rcvr,
+            method.sig.c_variadic,
+            tuple_arguments,
+            self.tcx.hir().span_if_local(method.def_id),
+        );
+        method.sig.output()
+    }
+
+    /// Generic function that factors out common logic from function calls,
+    /// method calls and overloaded operators.
+    pub(in super::super) fn check_argument_types(
+        &self,
+        sp: Span,
+        expr: &'tcx hir::Expr<'tcx>,
+        fn_inputs: &[Ty<'tcx>],
+        expected_arg_tys: &[Ty<'tcx>],
+        args: &'tcx [hir::Expr<'tcx>],
+        c_variadic: bool,
+        tuple_arguments: TupleArgumentsFlag,
+        def_span: Option<Span>,
+    ) {
+        let tcx = self.tcx;
+        // Grab the argument types, supplying fresh type variables
+        // if the wrong number of arguments were supplied
+        let supplied_arg_count = if tuple_arguments == DontTupleArguments { args.len() } else { 1 };
+
+        // All the input types from the fn signature must outlive the call
+        // so as to validate implied bounds.
+        for (&fn_input_ty, arg_expr) in fn_inputs.iter().zip(args.iter()) {
+            self.register_wf_obligation(fn_input_ty.into(), arg_expr.span, traits::MiscObligation);
+        }
+
+        let expected_arg_count = fn_inputs.len();
+
+        let param_count_error = |expected_count: usize,
+                                 arg_count: usize,
+                                 error_code: &str,
+                                 c_variadic: bool,
+                                 sugg_unit: bool| {
+            let (span, start_span, args) = match &expr.kind {
+                hir::ExprKind::Call(hir::Expr { span, .. }, args) => (*span, *span, &args[..]),
+                hir::ExprKind::MethodCall(path_segment, span, args, _) => (
+                    *span,
+                    // `sp` doesn't point at the whole `foo.bar()`, only at `bar`.
+                    path_segment
+                        .args
+                        .and_then(|args| args.args.iter().last())
+                        // Account for `foo.bar::<T>()`.
+                        .map(|arg| {
+                            // Skip the closing `>`.
+                            tcx.sess
+                                .source_map()
+                                .next_point(tcx.sess.source_map().next_point(arg.span()))
+                        })
+                        .unwrap_or(*span),
+                    &args[1..], // Skip the receiver.
+                ),
+                k => span_bug!(sp, "checking argument types on a non-call: `{:?}`", k),
+            };
+            let arg_spans = if args.is_empty() {
+                // foo()
+                // ^^^-- supplied 0 arguments
+                // |
+                // expected 2 arguments
+                vec![tcx.sess.source_map().next_point(start_span).with_hi(sp.hi())]
+            } else {
+                // foo(1, 2, 3)
+                // ^^^ -  -  - supplied 3 arguments
+                // |
+                // expected 2 arguments
+                args.iter().map(|arg| arg.span).collect::<Vec<Span>>()
+            };
+
+            let mut err = tcx.sess.struct_span_err_with_code(
+                span,
+                &format!(
+                    "this function takes {}{} but {} {} supplied",
+                    if c_variadic { "at least " } else { "" },
+                    potentially_plural_count(expected_count, "argument"),
+                    potentially_plural_count(arg_count, "argument"),
+                    if arg_count == 1 { "was" } else { "were" }
+                ),
+                DiagnosticId::Error(error_code.to_owned()),
+            );
+            let label = format!("supplied {}", potentially_plural_count(arg_count, "argument"));
+            for (i, span) in arg_spans.into_iter().enumerate() {
+                err.span_label(
+                    span,
+                    if arg_count == 0 || i + 1 == arg_count { &label } else { "" },
+                );
+            }
+
+            if let Some(def_s) = def_span.map(|sp| tcx.sess.source_map().guess_head_span(sp)) {
+                err.span_label(def_s, "defined here");
+            }
+            if sugg_unit {
+                let sugg_span = tcx.sess.source_map().end_point(expr.span);
+                // remove closing `)` from the span
+                let sugg_span = sugg_span.shrink_to_lo();
+                err.span_suggestion(
+                    sugg_span,
+                    "expected the unit value `()`; create it with empty parentheses",
+                    String::from("()"),
+                    Applicability::MachineApplicable,
+                );
+            } else {
+                err.span_label(
+                    span,
+                    format!(
+                        "expected {}{}",
+                        if c_variadic { "at least " } else { "" },
+                        potentially_plural_count(expected_count, "argument")
+                    ),
+                );
+            }
+            err.emit();
+        };
+
+        let mut expected_arg_tys = expected_arg_tys.to_vec();
+
+        let formal_tys = if tuple_arguments == TupleArguments {
+            let tuple_type = self.structurally_resolved_type(sp, fn_inputs[0]);
+            match tuple_type.kind() {
+                ty::Tuple(arg_types) if arg_types.len() != args.len() => {
+                    param_count_error(arg_types.len(), args.len(), "E0057", false, false);
+                    expected_arg_tys = vec![];
+                    self.err_args(args.len())
+                }
+                ty::Tuple(arg_types) => {
+                    expected_arg_tys = match expected_arg_tys.get(0) {
+                        Some(&ty) => match ty.kind() {
+                            ty::Tuple(ref tys) => tys.iter().map(|k| k.expect_ty()).collect(),
+                            _ => vec![],
+                        },
+                        None => vec![],
+                    };
+                    arg_types.iter().map(|k| k.expect_ty()).collect()
+                }
+                _ => {
+                    struct_span_err!(
+                        tcx.sess,
+                        sp,
+                        E0059,
+                        "cannot use call notation; the first type parameter \
+                         for the function trait is neither a tuple nor unit"
+                    )
+                    .emit();
+                    expected_arg_tys = vec![];
+                    self.err_args(args.len())
+                }
+            }
+        } else if expected_arg_count == supplied_arg_count {
+            fn_inputs.to_vec()
+        } else if c_variadic {
+            if supplied_arg_count >= expected_arg_count {
+                fn_inputs.to_vec()
+            } else {
+                param_count_error(expected_arg_count, supplied_arg_count, "E0060", true, false);
+                expected_arg_tys = vec![];
+                self.err_args(supplied_arg_count)
+            }
+        } else {
+            // is the missing argument of type `()`?
+            let sugg_unit = if expected_arg_tys.len() == 1 && supplied_arg_count == 0 {
+                self.resolve_vars_if_possible(&expected_arg_tys[0]).is_unit()
+            } else if fn_inputs.len() == 1 && supplied_arg_count == 0 {
+                self.resolve_vars_if_possible(&fn_inputs[0]).is_unit()
+            } else {
+                false
+            };
+            param_count_error(expected_arg_count, supplied_arg_count, "E0061", false, sugg_unit);
+
+            expected_arg_tys = vec![];
+            self.err_args(supplied_arg_count)
+        };
+
+        debug!(
+            "check_argument_types: formal_tys={:?}",
+            formal_tys.iter().map(|t| self.ty_to_string(*t)).collect::<Vec<String>>()
+        );
+
+        // If there is no expectation, expect formal_tys.
+        let expected_arg_tys =
+            if !expected_arg_tys.is_empty() { expected_arg_tys } else { formal_tys.clone() };
+
+        let mut final_arg_types: Vec<(usize, Ty<'_>, Ty<'_>)> = vec![];
+
+        // Check the arguments.
+        // We do this in a pretty awful way: first we type-check any arguments
+        // that are not closures, then we type-check the closures. This is so
+        // that we have more information about the types of arguments when we
+        // type-check the functions. This isn't really the right way to do this.
+        for &check_closures in &[false, true] {
+            debug!("check_closures={}", check_closures);
+
+            // More awful hacks: before we check argument types, try to do
+            // an "opportunistic" trait resolution of any trait bounds on
+            // the call. This helps coercions.
+            if check_closures {
+                self.select_obligations_where_possible(false, |errors| {
+                    self.point_at_type_arg_instead_of_call_if_possible(errors, expr);
+                    self.point_at_arg_instead_of_call_if_possible(
+                        errors,
+                        &final_arg_types[..],
+                        sp,
+                        &args,
+                    );
+                })
+            }
+
+            // For C-variadic functions, we don't have a declared type for all of
+            // the arguments hence we only do our usual type checking with
+            // the arguments who's types we do know.
+            let t = if c_variadic {
+                expected_arg_count
+            } else if tuple_arguments == TupleArguments {
+                args.len()
+            } else {
+                supplied_arg_count
+            };
+            for (i, arg) in args.iter().take(t).enumerate() {
+                // Warn only for the first loop (the "no closures" one).
+                // Closure arguments themselves can't be diverging, but
+                // a previous argument can, e.g., `foo(panic!(), || {})`.
+                if !check_closures {
+                    self.warn_if_unreachable(arg.hir_id, arg.span, "expression");
+                }
+
+                let is_closure = match arg.kind {
+                    ExprKind::Closure(..) => true,
+                    _ => false,
+                };
+
+                if is_closure != check_closures {
+                    continue;
+                }
+
+                debug!("checking the argument");
+                let formal_ty = formal_tys[i];
+
+                // The special-cased logic below has three functions:
+                // 1. Provide as good of an expected type as possible.
+                let expected = Expectation::rvalue_hint(self, expected_arg_tys[i]);
+
+                let checked_ty = self.check_expr_with_expectation(&arg, expected);
+
+                // 2. Coerce to the most detailed type that could be coerced
+                //    to, which is `expected_ty` if `rvalue_hint` returns an
+                //    `ExpectHasType(expected_ty)`, or the `formal_ty` otherwise.
+                let coerce_ty = expected.only_has_type(self).unwrap_or(formal_ty);
+                // We're processing function arguments so we definitely want to use
+                // two-phase borrows.
+                self.demand_coerce(&arg, checked_ty, coerce_ty, None, AllowTwoPhase::Yes);
+                final_arg_types.push((i, checked_ty, coerce_ty));
+
+                // 3. Relate the expected type and the formal one,
+                //    if the expected type was used for the coercion.
+                self.demand_suptype(arg.span, formal_ty, coerce_ty);
+            }
+        }
+
+        // We also need to make sure we at least write the ty of the other
+        // arguments which we skipped above.
+        if c_variadic {
+            fn variadic_error<'tcx>(s: &Session, span: Span, t: Ty<'tcx>, cast_ty: &str) {
+                use crate::structured_errors::{StructuredDiagnostic, VariadicError};
+                VariadicError::new(s, span, t, cast_ty).diagnostic().emit();
+            }
+
+            for arg in args.iter().skip(expected_arg_count) {
+                let arg_ty = self.check_expr(&arg);
+
+                // There are a few types which get autopromoted when passed via varargs
+                // in C but we just error out instead and require explicit casts.
+                let arg_ty = self.structurally_resolved_type(arg.span, arg_ty);
+                match arg_ty.kind() {
+                    ty::Float(ast::FloatTy::F32) => {
+                        variadic_error(tcx.sess, arg.span, arg_ty, "c_double");
+                    }
+                    ty::Int(ast::IntTy::I8 | ast::IntTy::I16) | ty::Bool => {
+                        variadic_error(tcx.sess, arg.span, arg_ty, "c_int");
+                    }
+                    ty::Uint(ast::UintTy::U8 | ast::UintTy::U16) => {
+                        variadic_error(tcx.sess, arg.span, arg_ty, "c_uint");
+                    }
+                    ty::FnDef(..) => {
+                        let ptr_ty = self.tcx.mk_fn_ptr(arg_ty.fn_sig(self.tcx));
+                        let ptr_ty = self.resolve_vars_if_possible(&ptr_ty);
+                        variadic_error(tcx.sess, arg.span, arg_ty, &ptr_ty.to_string());
+                    }
+                    _ => {}
+                }
+            }
+        }
+    }
+
+    // AST fragment checking
+    pub(in super::super) fn check_lit(
+        &self,
+        lit: &hir::Lit,
+        expected: Expectation<'tcx>,
+    ) -> Ty<'tcx> {
+        let tcx = self.tcx;
+
+        match lit.node {
+            ast::LitKind::Str(..) => tcx.mk_static_str(),
+            ast::LitKind::ByteStr(ref v) => {
+                tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_array(tcx.types.u8, v.len() as u64))
+            }
+            ast::LitKind::Byte(_) => tcx.types.u8,
+            ast::LitKind::Char(_) => tcx.types.char,
+            ast::LitKind::Int(_, ast::LitIntType::Signed(t)) => tcx.mk_mach_int(t),
+            ast::LitKind::Int(_, ast::LitIntType::Unsigned(t)) => tcx.mk_mach_uint(t),
+            ast::LitKind::Int(_, ast::LitIntType::Unsuffixed) => {
+                let opt_ty = expected.to_option(self).and_then(|ty| match ty.kind() {
+                    ty::Int(_) | ty::Uint(_) => Some(ty),
+                    ty::Char => Some(tcx.types.u8),
+                    ty::RawPtr(..) => Some(tcx.types.usize),
+                    ty::FnDef(..) | ty::FnPtr(_) => Some(tcx.types.usize),
+                    _ => None,
+                });
+                opt_ty.unwrap_or_else(|| self.next_int_var())
+            }
+            ast::LitKind::Float(_, ast::LitFloatType::Suffixed(t)) => tcx.mk_mach_float(t),
+            ast::LitKind::Float(_, ast::LitFloatType::Unsuffixed) => {
+                let opt_ty = expected.to_option(self).and_then(|ty| match ty.kind() {
+                    ty::Float(_) => Some(ty),
+                    _ => None,
+                });
+                opt_ty.unwrap_or_else(|| self.next_float_var())
+            }
+            ast::LitKind::Bool(_) => tcx.types.bool,
+            ast::LitKind::Err(_) => tcx.ty_error(),
+        }
+    }
+
+    pub fn check_struct_path(
+        &self,
+        qpath: &QPath<'_>,
+        hir_id: hir::HirId,
+    ) -> Option<(&'tcx ty::VariantDef, Ty<'tcx>)> {
+        let path_span = qpath.qself_span();
+        let (def, ty) = self.finish_resolving_struct_path(qpath, path_span, hir_id);
+        let variant = match def {
+            Res::Err => {
+                self.set_tainted_by_errors();
+                return None;
+            }
+            Res::Def(DefKind::Variant, _) => match ty.kind() {
+                ty::Adt(adt, substs) => Some((adt.variant_of_res(def), adt.did, substs)),
+                _ => bug!("unexpected type: {:?}", ty),
+            },
+            Res::Def(DefKind::Struct | DefKind::Union | DefKind::TyAlias | DefKind::AssocTy, _)
+            | Res::SelfTy(..) => match ty.kind() {
+                ty::Adt(adt, substs) if !adt.is_enum() => {
+                    Some((adt.non_enum_variant(), adt.did, substs))
+                }
+                _ => None,
+            },
+            _ => bug!("unexpected definition: {:?}", def),
+        };
+
+        if let Some((variant, did, substs)) = variant {
+            debug!("check_struct_path: did={:?} substs={:?}", did, substs);
+            self.write_user_type_annotation_from_substs(hir_id, did, substs, None);
+
+            // Check bounds on type arguments used in the path.
+            let (bounds, _) = self.instantiate_bounds(path_span, did, substs);
+            let cause =
+                traits::ObligationCause::new(path_span, self.body_id, traits::ItemObligation(did));
+            self.add_obligations_for_parameters(cause, bounds);
+
+            Some((variant, ty))
+        } else {
+            struct_span_err!(
+                self.tcx.sess,
+                path_span,
+                E0071,
+                "expected struct, variant or union type, found {}",
+                ty.sort_string(self.tcx)
+            )
+            .span_label(path_span, "not a struct")
+            .emit();
+            None
+        }
+    }
+
+    pub fn check_decl_initializer(
+        &self,
+        local: &'tcx hir::Local<'tcx>,
+        init: &'tcx hir::Expr<'tcx>,
+    ) -> Ty<'tcx> {
+        // FIXME(tschottdorf): `contains_explicit_ref_binding()` must be removed
+        // for #42640 (default match binding modes).
+        //
+        // See #44848.
+        let ref_bindings = local.pat.contains_explicit_ref_binding();
+
+        let local_ty = self.local_ty(init.span, local.hir_id).revealed_ty;
+        if let Some(m) = ref_bindings {
+            // Somewhat subtle: if we have a `ref` binding in the pattern,
+            // we want to avoid introducing coercions for the RHS. This is
+            // both because it helps preserve sanity and, in the case of
+            // ref mut, for soundness (issue #23116). In particular, in
+            // the latter case, we need to be clear that the type of the
+            // referent for the reference that results is *equal to* the
+            // type of the place it is referencing, and not some
+            // supertype thereof.
+            let init_ty = self.check_expr_with_needs(init, Needs::maybe_mut_place(m));
+            self.demand_eqtype(init.span, local_ty, init_ty);
+            init_ty
+        } else {
+            self.check_expr_coercable_to_type(init, local_ty, None)
+        }
+    }
+
+    /// Type check a `let` statement.
+    pub fn check_decl_local(&self, local: &'tcx hir::Local<'tcx>) {
+        // Determine and write the type which we'll check the pattern against.
+        let ty = self.local_ty(local.span, local.hir_id).decl_ty;
+        self.write_ty(local.hir_id, ty);
+
+        // Type check the initializer.
+        if let Some(ref init) = local.init {
+            let init_ty = self.check_decl_initializer(local, &init);
+            self.overwrite_local_ty_if_err(local, ty, init_ty);
+        }
+
+        // Does the expected pattern type originate from an expression and what is the span?
+        let (origin_expr, ty_span) = match (local.ty, local.init) {
+            (Some(ty), _) => (false, Some(ty.span)), // Bias towards the explicit user type.
+            (_, Some(init)) => (true, Some(init.span)), // No explicit type; so use the scrutinee.
+            _ => (false, None), // We have `let $pat;`, so the expected type is unconstrained.
+        };
+
+        // Type check the pattern. Override if necessary to avoid knock-on errors.
+        self.check_pat_top(&local.pat, ty, ty_span, origin_expr);
+        let pat_ty = self.node_ty(local.pat.hir_id);
+        self.overwrite_local_ty_if_err(local, ty, pat_ty);
+    }
+
+    pub fn check_stmt(&self, stmt: &'tcx hir::Stmt<'tcx>) {
+        // Don't do all the complex logic below for `DeclItem`.
+        match stmt.kind {
+            hir::StmtKind::Item(..) => return,
+            hir::StmtKind::Local(..) | hir::StmtKind::Expr(..) | hir::StmtKind::Semi(..) => {}
+        }
+
+        self.warn_if_unreachable(stmt.hir_id, stmt.span, "statement");
+
+        // Hide the outer diverging and `has_errors` flags.
+        let old_diverges = self.diverges.replace(Diverges::Maybe);
+        let old_has_errors = self.has_errors.replace(false);
+
+        match stmt.kind {
+            hir::StmtKind::Local(ref l) => {
+                self.check_decl_local(&l);
+            }
+            // Ignore for now.
+            hir::StmtKind::Item(_) => {}
+            hir::StmtKind::Expr(ref expr) => {
+                // Check with expected type of `()`.
+                self.check_expr_has_type_or_error(&expr, self.tcx.mk_unit(), |err| {
+                    self.suggest_semicolon_at_end(expr.span, err);
+                });
+            }
+            hir::StmtKind::Semi(ref expr) => {
+                self.check_expr(&expr);
+            }
+        }
+
+        // Combine the diverging and `has_error` flags.
+        self.diverges.set(self.diverges.get() | old_diverges);
+        self.has_errors.set(self.has_errors.get() | old_has_errors);
+    }
+
+    pub fn check_block_no_value(&self, blk: &'tcx hir::Block<'tcx>) {
+        let unit = self.tcx.mk_unit();
+        let ty = self.check_block_with_expected(blk, ExpectHasType(unit));
+
+        // if the block produces a `!` value, that can always be
+        // (effectively) coerced to unit.
+        if !ty.is_never() {
+            self.demand_suptype(blk.span, unit, ty);
+        }
+    }
+
+    pub(in super::super) fn check_block_with_expected(
+        &self,
+        blk: &'tcx hir::Block<'tcx>,
+        expected: Expectation<'tcx>,
+    ) -> Ty<'tcx> {
+        let prev = {
+            let mut fcx_ps = self.ps.borrow_mut();
+            let unsafety_state = fcx_ps.recurse(blk);
+            replace(&mut *fcx_ps, unsafety_state)
+        };
+
+        // In some cases, blocks have just one exit, but other blocks
+        // can be targeted by multiple breaks. This can happen both
+        // with labeled blocks as well as when we desugar
+        // a `try { ... }` expression.
+        //
+        // Example 1:
+        //
+        //    'a: { if true { break 'a Err(()); } Ok(()) }
+        //
+        // Here we would wind up with two coercions, one from
+        // `Err(())` and the other from the tail expression
+        // `Ok(())`. If the tail expression is omitted, that's a
+        // "forced unit" -- unless the block diverges, in which
+        // case we can ignore the tail expression (e.g., `'a: {
+        // break 'a 22; }` would not force the type of the block
+        // to be `()`).
+        let tail_expr = blk.expr.as_ref();
+        let coerce_to_ty = expected.coercion_target_type(self, blk.span);
+        let coerce = if blk.targeted_by_break {
+            CoerceMany::new(coerce_to_ty)
+        } else {
+            let tail_expr: &[&hir::Expr<'_>] = match tail_expr {
+                Some(e) => slice::from_ref(e),
+                None => &[],
+            };
+            CoerceMany::with_coercion_sites(coerce_to_ty, tail_expr)
+        };
+
+        let prev_diverges = self.diverges.get();
+        let ctxt = BreakableCtxt { coerce: Some(coerce), may_break: false };
+
+        let (ctxt, ()) = self.with_breakable_ctxt(blk.hir_id, ctxt, || {
+            for s in blk.stmts {
+                self.check_stmt(s);
+            }
+
+            // check the tail expression **without** holding the
+            // `enclosing_breakables` lock below.
+            let tail_expr_ty = tail_expr.map(|t| self.check_expr_with_expectation(t, expected));
+
+            let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
+            let ctxt = enclosing_breakables.find_breakable(blk.hir_id);
+            let coerce = ctxt.coerce.as_mut().unwrap();
+            if let Some(tail_expr_ty) = tail_expr_ty {
+                let tail_expr = tail_expr.unwrap();
+                let span = self.get_expr_coercion_span(tail_expr);
+                let cause = self.cause(span, ObligationCauseCode::BlockTailExpression(blk.hir_id));
+                coerce.coerce(self, &cause, tail_expr, tail_expr_ty);
+            } else {
+                // Subtle: if there is no explicit tail expression,
+                // that is typically equivalent to a tail expression
+                // of `()` -- except if the block diverges. In that
+                // case, there is no value supplied from the tail
+                // expression (assuming there are no other breaks,
+                // this implies that the type of the block will be
+                // `!`).
+                //
+                // #41425 -- label the implicit `()` as being the
+                // "found type" here, rather than the "expected type".
+                if !self.diverges.get().is_always() {
+                    // #50009 -- Do not point at the entire fn block span, point at the return type
+                    // span, as it is the cause of the requirement, and
+                    // `consider_hint_about_removing_semicolon` will point at the last expression
+                    // if it were a relevant part of the error. This improves usability in editors
+                    // that highlight errors inline.
+                    let mut sp = blk.span;
+                    let mut fn_span = None;
+                    if let Some((decl, ident)) = self.get_parent_fn_decl(blk.hir_id) {
+                        let ret_sp = decl.output.span();
+                        if let Some(block_sp) = self.parent_item_span(blk.hir_id) {
+                            // HACK: on some cases (`ui/liveness/liveness-issue-2163.rs`) the
+                            // output would otherwise be incorrect and even misleading. Make sure
+                            // the span we're aiming at correspond to a `fn` body.
+                            if block_sp == blk.span {
+                                sp = ret_sp;
+                                fn_span = Some(ident.span);
+                            }
+                        }
+                    }
+                    coerce.coerce_forced_unit(
+                        self,
+                        &self.misc(sp),
+                        &mut |err| {
+                            if let Some(expected_ty) = expected.only_has_type(self) {
+                                self.consider_hint_about_removing_semicolon(blk, expected_ty, err);
+                            }
+                            if let Some(fn_span) = fn_span {
+                                err.span_label(
+                                    fn_span,
+                                    "implicitly returns `()` as its body has no tail or `return` \
+                                     expression",
+                                );
+                            }
+                        },
+                        false,
+                    );
+                }
+            }
+        });
+
+        if ctxt.may_break {
+            // If we can break from the block, then the block's exit is always reachable
+            // (... as long as the entry is reachable) - regardless of the tail of the block.
+            self.diverges.set(prev_diverges);
+        }
+
+        let mut ty = ctxt.coerce.unwrap().complete(self);
+
+        if self.has_errors.get() || ty.references_error() {
+            ty = self.tcx.ty_error()
+        }
+
+        self.write_ty(blk.hir_id, ty);
+
+        *self.ps.borrow_mut() = prev;
+        ty
+    }
+
+    pub(in super::super) fn check_rustc_args_require_const(
+        &self,
+        def_id: DefId,
+        hir_id: hir::HirId,
+        span: Span,
+    ) {
+        // We're only interested in functions tagged with
+        // #[rustc_args_required_const], so ignore anything that's not.
+        if !self.tcx.has_attr(def_id, sym::rustc_args_required_const) {
+            return;
+        }
+
+        // If our calling expression is indeed the function itself, we're good!
+        // If not, generate an error that this can only be called directly.
+        if let Node::Expr(expr) = self.tcx.hir().get(self.tcx.hir().get_parent_node(hir_id)) {
+            if let ExprKind::Call(ref callee, ..) = expr.kind {
+                if callee.hir_id == hir_id {
+                    return;
+                }
+            }
+        }
+
+        self.tcx.sess.span_err(
+            span,
+            "this function can only be invoked directly, not through a function pointer",
+        );
+    }
+
+    /// A common error is to add an extra semicolon:
+    ///
+    /// ```
+    /// fn foo() -> usize {
+    ///     22;
+    /// }
+    /// ```
+    ///
+    /// This routine checks if the final statement in a block is an
+    /// expression with an explicit semicolon whose type is compatible
+    /// with `expected_ty`. If so, it suggests removing the semicolon.
+    fn consider_hint_about_removing_semicolon(
+        &self,
+        blk: &'tcx hir::Block<'tcx>,
+        expected_ty: Ty<'tcx>,
+        err: &mut DiagnosticBuilder<'_>,
+    ) {
+        if let Some(span_semi) = self.could_remove_semicolon(blk, expected_ty) {
+            err.span_suggestion(
+                span_semi,
+                "consider removing this semicolon",
+                String::new(),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+
+    fn parent_item_span(&self, id: hir::HirId) -> Option<Span> {
+        let node = self.tcx.hir().get(self.tcx.hir().get_parent_item(id));
+        match node {
+            Node::Item(&hir::Item { kind: hir::ItemKind::Fn(_, _, body_id), .. })
+            | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(_, body_id), .. }) => {
+                let body = self.tcx.hir().body(body_id);
+                if let ExprKind::Block(block, _) = &body.value.kind {
+                    return Some(block.span);
+                }
+            }
+            _ => {}
+        }
+        None
+    }
+
+    /// Given a function block's `HirId`, returns its `FnDecl` if it exists, or `None` otherwise.
+    fn get_parent_fn_decl(&self, blk_id: hir::HirId) -> Option<(&'tcx hir::FnDecl<'tcx>, Ident)> {
+        let parent = self.tcx.hir().get(self.tcx.hir().get_parent_item(blk_id));
+        self.get_node_fn_decl(parent).map(|(fn_decl, ident, _)| (fn_decl, ident))
+    }
+
+    /// If `expr` is a `match` expression that has only one non-`!` arm, use that arm's tail
+    /// expression's `Span`, otherwise return `expr.span`. This is done to give better errors
+    /// when given code like the following:
+    /// ```text
+    /// if false { return 0i32; } else { 1u32 }
+    /// //                               ^^^^ point at this instead of the whole `if` expression
+    /// ```
+    fn get_expr_coercion_span(&self, expr: &hir::Expr<'_>) -> rustc_span::Span {
+        if let hir::ExprKind::Match(_, arms, _) = &expr.kind {
+            let arm_spans: Vec<Span> = arms
+                .iter()
+                .filter_map(|arm| {
+                    self.in_progress_typeck_results
+                        .and_then(|typeck_results| {
+                            typeck_results.borrow().node_type_opt(arm.body.hir_id)
+                        })
+                        .and_then(|arm_ty| {
+                            if arm_ty.is_never() {
+                                None
+                            } else {
+                                Some(match &arm.body.kind {
+                                    // Point at the tail expression when possible.
+                                    hir::ExprKind::Block(block, _) => {
+                                        block.expr.as_ref().map(|e| e.span).unwrap_or(block.span)
+                                    }
+                                    _ => arm.body.span,
+                                })
+                            }
+                        })
+                })
+                .collect();
+            if arm_spans.len() == 1 {
+                return arm_spans[0];
+            }
+        }
+        expr.span
+    }
+
+    fn overwrite_local_ty_if_err(
+        &self,
+        local: &'tcx hir::Local<'tcx>,
+        decl_ty: Ty<'tcx>,
+        ty: Ty<'tcx>,
+    ) {
+        if ty.references_error() {
+            // Override the types everywhere with `err()` to avoid knock on errors.
+            self.write_ty(local.hir_id, ty);
+            self.write_ty(local.pat.hir_id, ty);
+            let local_ty = LocalTy { decl_ty, revealed_ty: ty };
+            self.locals.borrow_mut().insert(local.hir_id, local_ty);
+            self.locals.borrow_mut().insert(local.pat.hir_id, local_ty);
+        }
+    }
+
+    // Finish resolving a path in a struct expression or pattern `S::A { .. }` if necessary.
+    // The newly resolved definition is written into `type_dependent_defs`.
+    fn finish_resolving_struct_path(
+        &self,
+        qpath: &QPath<'_>,
+        path_span: Span,
+        hir_id: hir::HirId,
+    ) -> (Res, Ty<'tcx>) {
+        match *qpath {
+            QPath::Resolved(ref maybe_qself, ref path) => {
+                let self_ty = maybe_qself.as_ref().map(|qself| self.to_ty(qself));
+                let ty = AstConv::res_to_ty(self, self_ty, path, true);
+                (path.res, ty)
+            }
+            QPath::TypeRelative(ref qself, ref segment) => {
+                let ty = self.to_ty(qself);
+
+                let res = if let hir::TyKind::Path(QPath::Resolved(_, ref path)) = qself.kind {
+                    path.res
+                } else {
+                    Res::Err
+                };
+                let result =
+                    AstConv::associated_path_to_ty(self, hir_id, path_span, ty, res, segment, true);
+                let ty = result.map(|(ty, _, _)| ty).unwrap_or_else(|_| self.tcx().ty_error());
+                let result = result.map(|(_, kind, def_id)| (kind, def_id));
+
+                // Write back the new resolution.
+                self.write_resolution(hir_id, result);
+
+                (result.map(|(kind, def_id)| Res::Def(kind, def_id)).unwrap_or(Res::Err), ty)
+            }
+            QPath::LangItem(lang_item, span) => {
+                self.resolve_lang_item_path(lang_item, span, hir_id)
+            }
+        }
+    }
+
+    /// Given a vec of evaluated `FulfillmentError`s and an `fn` call argument expressions, we walk
+    /// the checked and coerced types for each argument to see if any of the `FulfillmentError`s
+    /// reference a type argument. The reason to walk also the checked type is that the coerced type
+    /// can be not easily comparable with predicate type (because of coercion). If the types match
+    /// for either checked or coerced type, and there's only *one* argument that does, we point at
+    /// the corresponding argument's expression span instead of the `fn` call path span.
+    fn point_at_arg_instead_of_call_if_possible(
+        &self,
+        errors: &mut Vec<traits::FulfillmentError<'tcx>>,
+        final_arg_types: &[(usize, Ty<'tcx>, Ty<'tcx>)],
+        call_sp: Span,
+        args: &'tcx [hir::Expr<'tcx>],
+    ) {
+        // We *do not* do this for desugared call spans to keep good diagnostics when involving
+        // the `?` operator.
+        if call_sp.desugaring_kind().is_some() {
+            return;
+        }
+
+        for error in errors {
+            // Only if the cause is somewhere inside the expression we want try to point at arg.
+            // Otherwise, it means that the cause is somewhere else and we should not change
+            // anything because we can break the correct span.
+            if !call_sp.contains(error.obligation.cause.span) {
+                continue;
+            }
+
+            if let ty::PredicateAtom::Trait(predicate, _) =
+                error.obligation.predicate.skip_binders()
+            {
+                // Collect the argument position for all arguments that could have caused this
+                // `FulfillmentError`.
+                let mut referenced_in = final_arg_types
+                    .iter()
+                    .map(|&(i, checked_ty, _)| (i, checked_ty))
+                    .chain(final_arg_types.iter().map(|&(i, _, coerced_ty)| (i, coerced_ty)))
+                    .flat_map(|(i, ty)| {
+                        let ty = self.resolve_vars_if_possible(&ty);
+                        // We walk the argument type because the argument's type could have
+                        // been `Option<T>`, but the `FulfillmentError` references `T`.
+                        if ty.walk().any(|arg| arg == predicate.self_ty().into()) {
+                            Some(i)
+                        } else {
+                            None
+                        }
+                    })
+                    .collect::<Vec<usize>>();
+
+                // Both checked and coerced types could have matched, thus we need to remove
+                // duplicates.
+
+                // We sort primitive type usize here and can use unstable sort
+                referenced_in.sort_unstable();
+                referenced_in.dedup();
+
+                if let (Some(ref_in), None) = (referenced_in.pop(), referenced_in.pop()) {
+                    // We make sure that only *one* argument matches the obligation failure
+                    // and we assign the obligation's span to its expression's.
+                    error.obligation.cause.make_mut().span = args[ref_in].span;
+                    error.points_at_arg_span = true;
+                }
+            }
+        }
+    }
+
+    /// Given a vec of evaluated `FulfillmentError`s and an `fn` call expression, we walk the
+    /// `PathSegment`s and resolve their type parameters to see if any of the `FulfillmentError`s
+    /// were caused by them. If they were, we point at the corresponding type argument's span
+    /// instead of the `fn` call path span.
+    fn point_at_type_arg_instead_of_call_if_possible(
+        &self,
+        errors: &mut Vec<traits::FulfillmentError<'tcx>>,
+        call_expr: &'tcx hir::Expr<'tcx>,
+    ) {
+        if let hir::ExprKind::Call(path, _) = &call_expr.kind {
+            if let hir::ExprKind::Path(qpath) = &path.kind {
+                if let hir::QPath::Resolved(_, path) = &qpath {
+                    for error in errors {
+                        if let ty::PredicateAtom::Trait(predicate, _) =
+                            error.obligation.predicate.skip_binders()
+                        {
+                            // If any of the type arguments in this path segment caused the
+                            // `FullfillmentError`, point at its span (#61860).
+                            for arg in path
+                                .segments
+                                .iter()
+                                .filter_map(|seg| seg.args.as_ref())
+                                .flat_map(|a| a.args.iter())
+                            {
+                                if let hir::GenericArg::Type(hir_ty) = &arg {
+                                    if let hir::TyKind::Path(hir::QPath::TypeRelative(..)) =
+                                        &hir_ty.kind
+                                    {
+                                        // Avoid ICE with associated types. As this is best
+                                        // effort only, it's ok to ignore the case. It
+                                        // would trigger in `is_send::<T::AssocType>();`
+                                        // from `typeck-default-trait-impl-assoc-type.rs`.
+                                    } else {
+                                        let ty = AstConv::ast_ty_to_ty(self, hir_ty);
+                                        let ty = self.resolve_vars_if_possible(&ty);
+                                        if ty == predicate.self_ty() {
+                                            error.obligation.cause.make_mut().span = hir_ty.span;
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/compiler/rustc_typeck/src/check/fn_ctxt/mod.rs b/compiler/rustc_typeck/src/check/fn_ctxt/mod.rs
new file mode 100644
index 00000000000..72c3b233ed9
--- /dev/null
+++ b/compiler/rustc_typeck/src/check/fn_ctxt/mod.rs
@@ -0,0 +1,295 @@
+mod _impl;
+mod checks;
+mod suggestions;
+
+pub use _impl::*;
+pub use checks::*;
+pub use suggestions::*;
+
+use crate::astconv::AstConv;
+use crate::check::coercion::DynamicCoerceMany;
+use crate::check::{Diverges, EnclosingBreakables, Inherited, UnsafetyState};
+
+use rustc_hir as hir;
+use rustc_hir::def_id::DefId;
+use rustc_infer::infer;
+use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
+use rustc_infer::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
+use rustc_middle::hir::map::blocks::FnLikeNode;
+use rustc_middle::ty::fold::TypeFoldable;
+use rustc_middle::ty::subst::GenericArgKind;
+use rustc_middle::ty::{self, Const, Ty, TyCtxt};
+use rustc_session::Session;
+use rustc_span::{self, Span};
+use rustc_trait_selection::traits::{ObligationCause, ObligationCauseCode};
+
+use std::cell::{Cell, RefCell};
+use std::ops::Deref;
+
+pub struct FnCtxt<'a, 'tcx> {
+    pub(super) body_id: hir::HirId,
+
+    /// The parameter environment used for proving trait obligations
+    /// in this function. This can change when we descend into
+    /// closures (as they bring new things into scope), hence it is
+    /// not part of `Inherited` (as of the time of this writing,
+    /// closures do not yet change the environment, but they will
+    /// eventually).
+    pub(super) param_env: ty::ParamEnv<'tcx>,
+
+    /// Number of errors that had been reported when we started
+    /// checking this function. On exit, if we find that *more* errors
+    /// have been reported, we will skip regionck and other work that
+    /// expects the types within the function to be consistent.
+    // FIXME(matthewjasper) This should not exist, and it's not correct
+    // if type checking is run in parallel.
+    err_count_on_creation: usize,
+
+    /// If `Some`, this stores coercion information for returned
+    /// expressions. If `None`, this is in a context where return is
+    /// inappropriate, such as a const expression.
+    ///
+    /// This is a `RefCell<DynamicCoerceMany>`, which means that we
+    /// can track all the return expressions and then use them to
+    /// compute a useful coercion from the set, similar to a match
+    /// expression or other branching context. You can use methods
+    /// like `expected_ty` to access the declared return type (if
+    /// any).
+    pub(super) ret_coercion: Option<RefCell<DynamicCoerceMany<'tcx>>>,
+
+    pub(super) ret_coercion_impl_trait: Option<Ty<'tcx>>,
+
+    pub(super) ret_type_span: Option<Span>,
+
+    /// Used exclusively to reduce cost of advanced evaluation used for
+    /// more helpful diagnostics.
+    pub(super) in_tail_expr: bool,
+
+    /// First span of a return site that we find. Used in error messages.
+    pub(super) ret_coercion_span: RefCell<Option<Span>>,
+
+    pub(super) resume_yield_tys: Option<(Ty<'tcx>, Ty<'tcx>)>,
+
+    pub(super) ps: RefCell<UnsafetyState>,
+
+    /// Whether the last checked node generates a divergence (e.g.,
+    /// `return` will set this to `Always`). In general, when entering
+    /// an expression or other node in the tree, the initial value
+    /// indicates whether prior parts of the containing expression may
+    /// have diverged. It is then typically set to `Maybe` (and the
+    /// old value remembered) for processing the subparts of the
+    /// current expression. As each subpart is processed, they may set
+    /// the flag to `Always`, etc. Finally, at the end, we take the
+    /// result and "union" it with the original value, so that when we
+    /// return the flag indicates if any subpart of the parent
+    /// expression (up to and including this part) has diverged. So,
+    /// if you read it after evaluating a subexpression `X`, the value
+    /// you get indicates whether any subexpression that was
+    /// evaluating up to and including `X` diverged.
+    ///
+    /// We currently use this flag only for diagnostic purposes:
+    ///
+    /// - To warn about unreachable code: if, after processing a
+    ///   sub-expression but before we have applied the effects of the
+    ///   current node, we see that the flag is set to `Always`, we
+    ///   can issue a warning. This corresponds to something like
+    ///   `foo(return)`; we warn on the `foo()` expression. (We then
+    ///   update the flag to `WarnedAlways` to suppress duplicate
+    ///   reports.) Similarly, if we traverse to a fresh statement (or
+    ///   tail expression) from a `Always` setting, we will issue a
+    ///   warning. This corresponds to something like `{return;
+    ///   foo();}` or `{return; 22}`, where we would warn on the
+    ///   `foo()` or `22`.
+    ///
+    /// An expression represents dead code if, after checking it,
+    /// the diverges flag is set to something other than `Maybe`.
+    pub(super) diverges: Cell<Diverges>,
+
+    /// Whether any child nodes have any type errors.
+    pub(super) has_errors: Cell<bool>,
+
+    pub(super) enclosing_breakables: RefCell<EnclosingBreakables<'tcx>>,
+
+    pub(super) inh: &'a Inherited<'a, 'tcx>,
+}
+
+impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
+    pub fn new(
+        inh: &'a Inherited<'a, 'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        body_id: hir::HirId,
+    ) -> FnCtxt<'a, 'tcx> {
+        FnCtxt {
+            body_id,
+            param_env,
+            err_count_on_creation: inh.tcx.sess.err_count(),
+            ret_coercion: None,
+            ret_coercion_impl_trait: None,
+            ret_type_span: None,
+            in_tail_expr: false,
+            ret_coercion_span: RefCell::new(None),
+            resume_yield_tys: None,
+            ps: RefCell::new(UnsafetyState::function(hir::Unsafety::Normal, hir::CRATE_HIR_ID)),
+            diverges: Cell::new(Diverges::Maybe),
+            has_errors: Cell::new(false),
+            enclosing_breakables: RefCell::new(EnclosingBreakables {
+                stack: Vec::new(),
+                by_id: Default::default(),
+            }),
+            inh,
+        }
+    }
+
+    pub fn cause(&self, span: Span, code: ObligationCauseCode<'tcx>) -> ObligationCause<'tcx> {
+        ObligationCause::new(span, self.body_id, code)
+    }
+
+    pub fn misc(&self, span: Span) -> ObligationCause<'tcx> {
+        self.cause(span, ObligationCauseCode::MiscObligation)
+    }
+
+    pub fn sess(&self) -> &Session {
+        &self.tcx.sess
+    }
+
+    pub fn errors_reported_since_creation(&self) -> bool {
+        self.tcx.sess.err_count() > self.err_count_on_creation
+    }
+}
+
+impl<'a, 'tcx> Deref for FnCtxt<'a, 'tcx> {
+    type Target = Inherited<'a, 'tcx>;
+    fn deref(&self) -> &Self::Target {
+        &self.inh
+    }
+}
+
+impl<'a, 'tcx> AstConv<'tcx> for FnCtxt<'a, 'tcx> {
+    fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn item_def_id(&self) -> Option<DefId> {
+        None
+    }
+
+    fn default_constness_for_trait_bounds(&self) -> hir::Constness {
+        // FIXME: refactor this into a method
+        let node = self.tcx.hir().get(self.body_id);
+        if let Some(fn_like) = FnLikeNode::from_node(node) {
+            fn_like.constness()
+        } else {
+            hir::Constness::NotConst
+        }
+    }
+
+    fn get_type_parameter_bounds(&self, _: Span, def_id: DefId) -> ty::GenericPredicates<'tcx> {
+        let tcx = self.tcx;
+        let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
+        let item_id = tcx.hir().ty_param_owner(hir_id);
+        let item_def_id = tcx.hir().local_def_id(item_id);
+        let generics = tcx.generics_of(item_def_id);
+        let index = generics.param_def_id_to_index[&def_id];
+        ty::GenericPredicates {
+            parent: None,
+            predicates: tcx.arena.alloc_from_iter(
+                self.param_env.caller_bounds().iter().filter_map(|predicate| {
+                    match predicate.skip_binders() {
+                        ty::PredicateAtom::Trait(data, _) if data.self_ty().is_param(index) => {
+                            // HACK(eddyb) should get the original `Span`.
+                            let span = tcx.def_span(def_id);
+                            Some((predicate, span))
+                        }
+                        _ => None,
+                    }
+                }),
+            ),
+        }
+    }
+
+    fn re_infer(&self, def: Option<&ty::GenericParamDef>, span: Span) -> Option<ty::Region<'tcx>> {
+        let v = match def {
+            Some(def) => infer::EarlyBoundRegion(span, def.name),
+            None => infer::MiscVariable(span),
+        };
+        Some(self.next_region_var(v))
+    }
+
+    fn allow_ty_infer(&self) -> bool {
+        true
+    }
+
+    fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
+        if let Some(param) = param {
+            if let GenericArgKind::Type(ty) = self.var_for_def(span, param).unpack() {
+                return ty;
+            }
+            unreachable!()
+        } else {
+            self.next_ty_var(TypeVariableOrigin {
+                kind: TypeVariableOriginKind::TypeInference,
+                span,
+            })
+        }
+    }
+
+    fn ct_infer(
+        &self,
+        ty: Ty<'tcx>,
+        param: Option<&ty::GenericParamDef>,
+        span: Span,
+    ) -> &'tcx Const<'tcx> {
+        if let Some(param) = param {
+            if let GenericArgKind::Const(ct) = self.var_for_def(span, param).unpack() {
+                return ct;
+            }
+            unreachable!()
+        } else {
+            self.next_const_var(
+                ty,
+                ConstVariableOrigin { kind: ConstVariableOriginKind::ConstInference, span },
+            )
+        }
+    }
+
+    fn projected_ty_from_poly_trait_ref(
+        &self,
+        span: Span,
+        item_def_id: DefId,
+        item_segment: &hir::PathSegment<'_>,
+        poly_trait_ref: ty::PolyTraitRef<'tcx>,
+    ) -> Ty<'tcx> {
+        let (trait_ref, _) = self.replace_bound_vars_with_fresh_vars(
+            span,
+            infer::LateBoundRegionConversionTime::AssocTypeProjection(item_def_id),
+            &poly_trait_ref,
+        );
+
+        let item_substs = <dyn AstConv<'tcx>>::create_substs_for_associated_item(
+            self,
+            self.tcx,
+            span,
+            item_def_id,
+            item_segment,
+            trait_ref.substs,
+        );
+
+        self.tcx().mk_projection(item_def_id, item_substs)
+    }
+
+    fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
+        if ty.has_escaping_bound_vars() {
+            ty // FIXME: normalization and escaping regions
+        } else {
+            self.normalize_associated_types_in(span, &ty)
+        }
+    }
+
+    fn set_tainted_by_errors(&self) {
+        self.infcx.set_tainted_by_errors()
+    }
+
+    fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, _span: Span) {
+        self.write_ty(hir_id, ty)
+    }
+}
diff --git a/compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs b/compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs
new file mode 100644
index 00000000000..9bad02c41b4
--- /dev/null
+++ b/compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs
@@ -0,0 +1,528 @@
+use super::FnCtxt;
+use crate::astconv::AstConv;
+
+use rustc_ast::util::parser::ExprPrecedence;
+use rustc_span::{self, Span};
+use rustc_trait_selection::traits;
+
+use rustc_errors::{Applicability, DiagnosticBuilder};
+use rustc_hir as hir;
+use rustc_hir::def::{CtorOf, DefKind};
+use rustc_hir::lang_items::LangItem;
+use rustc_hir::{ExprKind, ItemKind, Node};
+use rustc_infer::infer;
+use rustc_middle::ty::{self, Ty};
+use rustc_span::symbol::kw;
+use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
+
+use std::iter;
+
+impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
+    pub(in super::super) fn suggest_semicolon_at_end(
+        &self,
+        span: Span,
+        err: &mut DiagnosticBuilder<'_>,
+    ) {
+        err.span_suggestion_short(
+            span.shrink_to_hi(),
+            "consider using a semicolon here",
+            ";".to_string(),
+            Applicability::MachineApplicable,
+        );
+    }
+
+    /// On implicit return expressions with mismatched types, provides the following suggestions:
+    ///
+    /// - Points out the method's return type as the reason for the expected type.
+    /// - Possible missing semicolon.
+    /// - Possible missing return type if the return type is the default, and not `fn main()`.
+    pub fn suggest_mismatched_types_on_tail(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        expr: &'tcx hir::Expr<'tcx>,
+        expected: Ty<'tcx>,
+        found: Ty<'tcx>,
+        cause_span: Span,
+        blk_id: hir::HirId,
+    ) -> bool {
+        let expr = expr.peel_drop_temps();
+        self.suggest_missing_semicolon(err, expr, expected, cause_span);
+        let mut pointing_at_return_type = false;
+        if let Some((fn_decl, can_suggest)) = self.get_fn_decl(blk_id) {
+            pointing_at_return_type =
+                self.suggest_missing_return_type(err, &fn_decl, expected, found, can_suggest);
+        }
+        pointing_at_return_type
+    }
+
+    /// When encountering an fn-like ctor that needs to unify with a value, check whether calling
+    /// the ctor would successfully solve the type mismatch and if so, suggest it:
+    /// ```
+    /// fn foo(x: usize) -> usize { x }
+    /// let x: usize = foo;  // suggest calling the `foo` function: `foo(42)`
+    /// ```
+    fn suggest_fn_call(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        expr: &hir::Expr<'_>,
+        expected: Ty<'tcx>,
+        found: Ty<'tcx>,
+    ) -> bool {
+        let hir = self.tcx.hir();
+        let (def_id, sig) = match *found.kind() {
+            ty::FnDef(def_id, _) => (def_id, found.fn_sig(self.tcx)),
+            ty::Closure(def_id, substs) => (def_id, substs.as_closure().sig()),
+            _ => return false,
+        };
+
+        let sig = self.replace_bound_vars_with_fresh_vars(expr.span, infer::FnCall, &sig).0;
+        let sig = self.normalize_associated_types_in(expr.span, &sig);
+        if self.can_coerce(sig.output(), expected) {
+            let (mut sugg_call, applicability) = if sig.inputs().is_empty() {
+                (String::new(), Applicability::MachineApplicable)
+            } else {
+                ("...".to_string(), Applicability::HasPlaceholders)
+            };
+            let mut msg = "call this function";
+            match hir.get_if_local(def_id) {
+                Some(
+                    Node::Item(hir::Item { kind: ItemKind::Fn(.., body_id), .. })
+                    | Node::ImplItem(hir::ImplItem {
+                        kind: hir::ImplItemKind::Fn(_, body_id), ..
+                    })
+                    | Node::TraitItem(hir::TraitItem {
+                        kind: hir::TraitItemKind::Fn(.., hir::TraitFn::Provided(body_id)),
+                        ..
+                    }),
+                ) => {
+                    let body = hir.body(*body_id);
+                    sugg_call = body
+                        .params
+                        .iter()
+                        .map(|param| match &param.pat.kind {
+                            hir::PatKind::Binding(_, _, ident, None)
+                                if ident.name != kw::SelfLower =>
+                            {
+                                ident.to_string()
+                            }
+                            _ => "_".to_string(),
+                        })
+                        .collect::<Vec<_>>()
+                        .join(", ");
+                }
+                Some(Node::Expr(hir::Expr {
+                    kind: ExprKind::Closure(_, _, body_id, _, _),
+                    span: full_closure_span,
+                    ..
+                })) => {
+                    if *full_closure_span == expr.span {
+                        return false;
+                    }
+                    msg = "call this closure";
+                    let body = hir.body(*body_id);
+                    sugg_call = body
+                        .params
+                        .iter()
+                        .map(|param| match &param.pat.kind {
+                            hir::PatKind::Binding(_, _, ident, None)
+                                if ident.name != kw::SelfLower =>
+                            {
+                                ident.to_string()
+                            }
+                            _ => "_".to_string(),
+                        })
+                        .collect::<Vec<_>>()
+                        .join(", ");
+                }
+                Some(Node::Ctor(hir::VariantData::Tuple(fields, _))) => {
+                    sugg_call = fields.iter().map(|_| "_").collect::<Vec<_>>().join(", ");
+                    match def_id.as_local().map(|def_id| hir.def_kind(def_id)) {
+                        Some(DefKind::Ctor(hir::def::CtorOf::Variant, _)) => {
+                            msg = "instantiate this tuple variant";
+                        }
+                        Some(DefKind::Ctor(CtorOf::Struct, _)) => {
+                            msg = "instantiate this tuple struct";
+                        }
+                        _ => {}
+                    }
+                }
+                Some(Node::ForeignItem(hir::ForeignItem {
+                    kind: hir::ForeignItemKind::Fn(_, idents, _),
+                    ..
+                })) => {
+                    sugg_call = idents
+                        .iter()
+                        .map(|ident| {
+                            if ident.name != kw::SelfLower {
+                                ident.to_string()
+                            } else {
+                                "_".to_string()
+                            }
+                        })
+                        .collect::<Vec<_>>()
+                        .join(", ")
+                }
+                Some(Node::TraitItem(hir::TraitItem {
+                    kind: hir::TraitItemKind::Fn(.., hir::TraitFn::Required(idents)),
+                    ..
+                })) => {
+                    sugg_call = idents
+                        .iter()
+                        .map(|ident| {
+                            if ident.name != kw::SelfLower {
+                                ident.to_string()
+                            } else {
+                                "_".to_string()
+                            }
+                        })
+                        .collect::<Vec<_>>()
+                        .join(", ")
+                }
+                _ => {}
+            }
+            err.span_suggestion_verbose(
+                expr.span.shrink_to_hi(),
+                &format!("use parentheses to {}", msg),
+                format!("({})", sugg_call),
+                applicability,
+            );
+            return true;
+        }
+        false
+    }
+
+    pub fn suggest_deref_ref_or_into(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        expr: &hir::Expr<'_>,
+        expected: Ty<'tcx>,
+        found: Ty<'tcx>,
+        expected_ty_expr: Option<&'tcx hir::Expr<'tcx>>,
+    ) {
+        if let Some((sp, msg, suggestion, applicability)) = self.check_ref(expr, found, expected) {
+            err.span_suggestion(sp, msg, suggestion, applicability);
+        } else if let (ty::FnDef(def_id, ..), true) =
+            (&found.kind(), self.suggest_fn_call(err, expr, expected, found))
+        {
+            if let Some(sp) = self.tcx.hir().span_if_local(*def_id) {
+                let sp = self.sess().source_map().guess_head_span(sp);
+                err.span_label(sp, &format!("{} defined here", found));
+            }
+        } else if !self.check_for_cast(err, expr, found, expected, expected_ty_expr) {
+            let is_struct_pat_shorthand_field =
+                self.is_hir_id_from_struct_pattern_shorthand_field(expr.hir_id, expr.span);
+            let methods = self.get_conversion_methods(expr.span, expected, found, expr.hir_id);
+            if let Ok(expr_text) = self.sess().source_map().span_to_snippet(expr.span) {
+                let mut suggestions = iter::repeat(&expr_text)
+                    .zip(methods.iter())
+                    .filter_map(|(receiver, method)| {
+                        let method_call = format!(".{}()", method.ident);
+                        if receiver.ends_with(&method_call) {
+                            None // do not suggest code that is already there (#53348)
+                        } else {
+                            let method_call_list = [".to_vec()", ".to_string()"];
+                            let sugg = if receiver.ends_with(".clone()")
+                                && method_call_list.contains(&method_call.as_str())
+                            {
+                                let max_len = receiver.rfind('.').unwrap();
+                                format!("{}{}", &receiver[..max_len], method_call)
+                            } else {
+                                if expr.precedence().order() < ExprPrecedence::MethodCall.order() {
+                                    format!("({}){}", receiver, method_call)
+                                } else {
+                                    format!("{}{}", receiver, method_call)
+                                }
+                            };
+                            Some(if is_struct_pat_shorthand_field {
+                                format!("{}: {}", receiver, sugg)
+                            } else {
+                                sugg
+                            })
+                        }
+                    })
+                    .peekable();
+                if suggestions.peek().is_some() {
+                    err.span_suggestions(
+                        expr.span,
+                        "try using a conversion method",
+                        suggestions,
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+            }
+        }
+    }
+
+    /// When encountering the expected boxed value allocated in the stack, suggest allocating it
+    /// in the heap by calling `Box::new()`.
+    pub(in super::super) fn suggest_boxing_when_appropriate(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        expr: &hir::Expr<'_>,
+        expected: Ty<'tcx>,
+        found: Ty<'tcx>,
+    ) {
+        if self.tcx.hir().is_inside_const_context(expr.hir_id) {
+            // Do not suggest `Box::new` in const context.
+            return;
+        }
+        if !expected.is_box() || found.is_box() {
+            return;
+        }
+        let boxed_found = self.tcx.mk_box(found);
+        if let (true, Ok(snippet)) = (
+            self.can_coerce(boxed_found, expected),
+            self.sess().source_map().span_to_snippet(expr.span),
+        ) {
+            err.span_suggestion(
+                expr.span,
+                "store this in the heap by calling `Box::new`",
+                format!("Box::new({})", snippet),
+                Applicability::MachineApplicable,
+            );
+            err.note(
+                "for more on the distinction between the stack and the heap, read \
+                 https://doc.rust-lang.org/book/ch15-01-box.html, \
+                 https://doc.rust-lang.org/rust-by-example/std/box.html, and \
+                 https://doc.rust-lang.org/std/boxed/index.html",
+            );
+        }
+    }
+
+    /// When encountering an `impl Future` where `BoxFuture` is expected, suggest `Box::pin`.
+    pub(in super::super) fn suggest_calling_boxed_future_when_appropriate(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        expr: &hir::Expr<'_>,
+        expected: Ty<'tcx>,
+        found: Ty<'tcx>,
+    ) -> bool {
+        // Handle #68197.
+
+        if self.tcx.hir().is_inside_const_context(expr.hir_id) {
+            // Do not suggest `Box::new` in const context.
+            return false;
+        }
+        let pin_did = self.tcx.lang_items().pin_type();
+        match expected.kind() {
+            ty::Adt(def, _) if Some(def.did) != pin_did => return false,
+            // This guards the `unwrap` and `mk_box` below.
+            _ if pin_did.is_none() || self.tcx.lang_items().owned_box().is_none() => return false,
+            _ => {}
+        }
+        let boxed_found = self.tcx.mk_box(found);
+        let new_found = self.tcx.mk_lang_item(boxed_found, LangItem::Pin).unwrap();
+        if let (true, Ok(snippet)) = (
+            self.can_coerce(new_found, expected),
+            self.sess().source_map().span_to_snippet(expr.span),
+        ) {
+            match found.kind() {
+                ty::Adt(def, _) if def.is_box() => {
+                    err.help("use `Box::pin`");
+                }
+                _ => {
+                    err.span_suggestion(
+                        expr.span,
+                        "you need to pin and box this expression",
+                        format!("Box::pin({})", snippet),
+                        Applicability::MachineApplicable,
+                    );
+                }
+            }
+            true
+        } else {
+            false
+        }
+    }
+
+    /// A common error is to forget to add a semicolon at the end of a block, e.g.,
+    ///
+    /// ```
+    /// fn foo() {
+    ///     bar_that_returns_u32()
+    /// }
+    /// ```
+    ///
+    /// This routine checks if the return expression in a block would make sense on its own as a
+    /// statement and the return type has been left as default or has been specified as `()`. If so,
+    /// it suggests adding a semicolon.
+    fn suggest_missing_semicolon(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        expression: &'tcx hir::Expr<'tcx>,
+        expected: Ty<'tcx>,
+        cause_span: Span,
+    ) {
+        if expected.is_unit() {
+            // `BlockTailExpression` only relevant if the tail expr would be
+            // useful on its own.
+            match expression.kind {
+                ExprKind::Call(..)
+                | ExprKind::MethodCall(..)
+                | ExprKind::Loop(..)
+                | ExprKind::Match(..)
+                | ExprKind::Block(..) => {
+                    err.span_suggestion(
+                        cause_span.shrink_to_hi(),
+                        "try adding a semicolon",
+                        ";".to_string(),
+                        Applicability::MachineApplicable,
+                    );
+                }
+                _ => (),
+            }
+        }
+    }
+
+    /// A possible error is to forget to add a return type that is needed:
+    ///
+    /// ```
+    /// fn foo() {
+    ///     bar_that_returns_u32()
+    /// }
+    /// ```
+    ///
+    /// This routine checks if the return type is left as default, the method is not part of an
+    /// `impl` block and that it isn't the `main` method. If so, it suggests setting the return
+    /// type.
+    pub(in super::super) fn suggest_missing_return_type(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        fn_decl: &hir::FnDecl<'_>,
+        expected: Ty<'tcx>,
+        found: Ty<'tcx>,
+        can_suggest: bool,
+    ) -> bool {
+        // Only suggest changing the return type for methods that
+        // haven't set a return type at all (and aren't `fn main()` or an impl).
+        match (&fn_decl.output, found.is_suggestable(), can_suggest, expected.is_unit()) {
+            (&hir::FnRetTy::DefaultReturn(span), true, true, true) => {
+                err.span_suggestion(
+                    span,
+                    "try adding a return type",
+                    format!("-> {} ", self.resolve_vars_with_obligations(found)),
+                    Applicability::MachineApplicable,
+                );
+                true
+            }
+            (&hir::FnRetTy::DefaultReturn(span), false, true, true) => {
+                err.span_label(span, "possibly return type missing here?");
+                true
+            }
+            (&hir::FnRetTy::DefaultReturn(span), _, false, true) => {
+                // `fn main()` must return `()`, do not suggest changing return type
+                err.span_label(span, "expected `()` because of default return type");
+                true
+            }
+            // expectation was caused by something else, not the default return
+            (&hir::FnRetTy::DefaultReturn(_), _, _, false) => false,
+            (&hir::FnRetTy::Return(ref ty), _, _, _) => {
+                // Only point to return type if the expected type is the return type, as if they
+                // are not, the expectation must have been caused by something else.
+                debug!("suggest_missing_return_type: return type {:?} node {:?}", ty, ty.kind);
+                let sp = ty.span;
+                let ty = AstConv::ast_ty_to_ty(self, ty);
+                debug!("suggest_missing_return_type: return type {:?}", ty);
+                debug!("suggest_missing_return_type: expected type {:?}", ty);
+                if ty.kind() == expected.kind() {
+                    err.span_label(sp, format!("expected `{}` because of return type", expected));
+                    return true;
+                }
+                false
+            }
+        }
+    }
+
+    /// A possible error is to forget to add `.await` when using futures:
+    ///
+    /// ```
+    /// async fn make_u32() -> u32 {
+    ///     22
+    /// }
+    ///
+    /// fn take_u32(x: u32) {}
+    ///
+    /// async fn foo() {
+    ///     let x = make_u32();
+    ///     take_u32(x);
+    /// }
+    /// ```
+    ///
+    /// This routine checks if the found type `T` implements `Future<Output=U>` where `U` is the
+    /// expected type. If this is the case, and we are inside of an async body, it suggests adding
+    /// `.await` to the tail of the expression.
+    pub(in super::super) fn suggest_missing_await(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        expr: &hir::Expr<'_>,
+        expected: Ty<'tcx>,
+        found: Ty<'tcx>,
+    ) {
+        debug!("suggest_missing_await: expr={:?} expected={:?}, found={:?}", expr, expected, found);
+        // `.await` is not permitted outside of `async` bodies, so don't bother to suggest if the
+        // body isn't `async`.
+        let item_id = self.tcx().hir().get_parent_node(self.body_id);
+        if let Some(body_id) = self.tcx().hir().maybe_body_owned_by(item_id) {
+            let body = self.tcx().hir().body(body_id);
+            if let Some(hir::GeneratorKind::Async(_)) = body.generator_kind {
+                let sp = expr.span;
+                // Check for `Future` implementations by constructing a predicate to
+                // prove: `<T as Future>::Output == U`
+                let future_trait = self.tcx.require_lang_item(LangItem::Future, Some(sp));
+                let item_def_id = self
+                    .tcx
+                    .associated_items(future_trait)
+                    .in_definition_order()
+                    .next()
+                    .unwrap()
+                    .def_id;
+                // `<T as Future>::Output`
+                let projection_ty = ty::ProjectionTy {
+                    // `T`
+                    substs: self
+                        .tcx
+                        .mk_substs_trait(found, self.fresh_substs_for_item(sp, item_def_id)),
+                    // `Future::Output`
+                    item_def_id,
+                };
+
+                let predicate = ty::PredicateAtom::Projection(ty::ProjectionPredicate {
+                    projection_ty,
+                    ty: expected,
+                })
+                .potentially_quantified(self.tcx, ty::PredicateKind::ForAll);
+                let obligation = traits::Obligation::new(self.misc(sp), self.param_env, predicate);
+
+                debug!("suggest_missing_await: trying obligation {:?}", obligation);
+
+                if self.infcx.predicate_may_hold(&obligation) {
+                    debug!("suggest_missing_await: obligation held: {:?}", obligation);
+                    if let Ok(code) = self.sess().source_map().span_to_snippet(sp) {
+                        err.span_suggestion(
+                            sp,
+                            "consider using `.await` here",
+                            format!("{}.await", code),
+                            Applicability::MaybeIncorrect,
+                        );
+                    } else {
+                        debug!("suggest_missing_await: no snippet for {:?}", sp);
+                    }
+                } else {
+                    debug!("suggest_missing_await: obligation did not hold: {:?}", obligation)
+                }
+            }
+        }
+    }
+
+    pub(in super::super) fn suggest_missing_parentheses(
+        &self,
+        err: &mut DiagnosticBuilder<'_>,
+        expr: &hir::Expr<'_>,
+    ) {
+        let sp = self.tcx.sess.source_map().start_point(expr.span);
+        if let Some(sp) = self.tcx.sess.parse_sess.ambiguous_block_expr_parse.borrow().get(&sp) {
+            // `{ 42 } &&x` (#61475) or `{ 42 } && if x { 1 } else { 0 }`
+            self.tcx.sess.parse_sess.expr_parentheses_needed(err, *sp, None);
+        }
+    }
+}
diff --git a/compiler/rustc_typeck/src/check/mod.rs b/compiler/rustc_typeck/src/check/mod.rs
index 1cb6ae21a47..24ffe944128 100644
--- a/compiler/rustc_typeck/src/check/mod.rs
+++ b/compiler/rustc_typeck/src/check/mod.rs
@@ -96,7 +96,7 @@ use check::{
 pub use check::{check_item_type, check_wf_new};
 pub use diverges::Diverges;
 pub use expectation::Expectation;
-pub use fn_ctxt::FnCtxt;
+pub use fn_ctxt::*;
 pub use inherited::{Inherited, InheritedBuilder};
 
 use crate::astconv::AstConv;