Auto merge of #128093 - matthiaskrgr:rollup-1snye4b, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - #125834 (treat `&raw (const|mut) UNSAFE_STATIC` implied deref as safe)
 - #127962 (Cleanup compiletest dylib name calculation)
 - #128049 (Reword E0626 to mention static coroutine, add structured suggestion for adding `static`)
 - #128067 (Get rid of `can_eq_shallow`)
 - #128076 (Get rid of `InferCtxtExt` from `error_reporting::traits`)
 - #128089 (std: Unsafe-wrap actually-universal platform code)

r? `@ghost`
`@rustbot` modify labels: rollup

10 files changed, 311 insertions, 277 deletions

diff --git a/compiler/rustc_borrowck/src/borrowck_errors.rs b/compiler/rustc_borrowck/src/borrowck_errors.rs
index 8eb44458137..80deea14685 100644
--- a/compiler/rustc_borrowck/src/borrowck_errors.rs
+++ b/compiler/rustc_borrowck/src/borrowck_errors.rs
@@ -1,7 +1,9 @@
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
 
+use rustc_errors::Applicability;
 use rustc_errors::{codes::*, struct_span_code_err, Diag, DiagCtxtHandle};
+use rustc_hir as hir;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::Span;
@@ -382,13 +384,35 @@ impl<'infcx, 'tcx> crate::MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         yield_span: Span,
     ) -> Diag<'infcx> {
         let coroutine_kind = self.body.coroutine.as_ref().unwrap().coroutine_kind;
-        struct_span_code_err!(
+        let mut diag = struct_span_code_err!(
             self.dcx(),
             span,
             E0626,
             "borrow may still be in use when {coroutine_kind:#} yields",
-        )
-        .with_span_label(yield_span, "possible yield occurs here")
+        );
+        diag.span_label(
+            self.infcx.tcx.def_span(self.body.source.def_id()),
+            format!("within this {coroutine_kind:#}"),
+        );
+        diag.span_label(yield_span, "possible yield occurs here");
+        if matches!(coroutine_kind, hir::CoroutineKind::Coroutine(_)) {
+            let hir::Closure { capture_clause, fn_decl_span, .. } = self
+                .infcx
+                .tcx
+                .hir_node_by_def_id(self.body.source.def_id().expect_local())
+                .expect_closure();
+            let span = match capture_clause {
+                rustc_hir::CaptureBy::Value { move_kw } => move_kw.shrink_to_lo(),
+                rustc_hir::CaptureBy::Ref => fn_decl_span.shrink_to_lo(),
+            };
+            diag.span_suggestion_verbose(
+                span,
+                "add `static` to mark this coroutine as unmovable",
+                "static ",
+                Applicability::MaybeIncorrect,
+            );
+        }
+        diag
     }
 
     pub(crate) fn cannot_borrow_across_destructor(&self, borrow_span: Span) -> Diag<'infcx> {
diff --git a/compiler/rustc_error_codes/src/error_codes/E0626.md b/compiler/rustc_error_codes/src/error_codes/E0626.md
index 28d543350ff..71c1f811aa7 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0626.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0626.md
@@ -1,4 +1,4 @@
-This error occurs because a borrow in a coroutine persists across a
+This error occurs because a borrow in a movable coroutine persists across a
 yield point.
 
 Erroneous code example:
@@ -15,19 +15,35 @@ let mut b = #[coroutine] || {
 Pin::new(&mut b).resume(());
 ```
 
-At present, it is not permitted to have a yield that occurs while a
-borrow is still in scope. To resolve this error, the borrow must
-either be "contained" to a smaller scope that does not overlap the
-yield or else eliminated in another way. So, for example, we might
-resolve the previous example by removing the borrow and just storing
-the integer by value:
+Coroutines may be either unmarked, or marked with `static`. If it is unmarked,
+then the coroutine is considered "movable". At present, it is not permitted to
+have a yield in a movable coroutine that occurs while a borrow is still in
+scope. To resolve this error, the coroutine may be marked `static`:
+
+```
+# #![feature(coroutines, coroutine_trait, stmt_expr_attributes)]
+# use std::ops::Coroutine;
+# use std::pin::Pin;
+let mut b = #[coroutine] static || { // <-- note the static keyword
+    let a = &String::from("hello, world");
+    yield ();
+    println!("{}", a);
+};
+let mut b = std::pin::pin!(b);
+b.as_mut().resume(());
+```
+
+If the coroutine must remain movable, for example to be used as `Unpin`
+without pinning it on the stack or in an allocation, we can alternatively
+resolve the previous example by removing the borrow and just storing the
+type by value:
 
 ```
 # #![feature(coroutines, coroutine_trait, stmt_expr_attributes)]
 # use std::ops::Coroutine;
 # use std::pin::Pin;
 let mut b = #[coroutine] || {
-    let a = 3;
+    let a = String::from("hello, world");
     yield ();
     println!("{}", a);
 };
diff --git a/compiler/rustc_hir_typeck/src/closure.rs b/compiler/rustc_hir_typeck/src/closure.rs
index 08de871f6fa..79854976bdd 100644
--- a/compiler/rustc_hir_typeck/src/closure.rs
+++ b/compiler/rustc_hir_typeck/src/closure.rs
@@ -18,7 +18,6 @@ use rustc_span::def_id::LocalDefId;
 use rustc_span::Span;
 use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::error_reporting::traits::ArgKind;
-use rustc_trait_selection::error_reporting::traits::InferCtxtExt as _;
 use rustc_trait_selection::traits;
 use rustc_type_ir::ClosureKind;
 use std::iter;
@@ -734,13 +733,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .map(|ty| ArgKind::from_expected_ty(*ty, None))
             .collect();
         let (closure_span, closure_arg_span, found_args) =
-            match self.get_fn_like_arguments(expr_map_node) {
+            match self.err_ctxt().get_fn_like_arguments(expr_map_node) {
                 Some((sp, arg_sp, args)) => (Some(sp), arg_sp, args),
                 None => (None, None, Vec::new()),
             };
         let expected_span =
             expected_sig.cause_span.unwrap_or_else(|| self.tcx.def_span(expr_def_id));
         let guar = self
+            .err_ctxt()
             .report_arg_count_mismatch(
                 expected_span,
                 closure_span,
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 7fc4e36d752..3cee0a622f1 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -755,18 +755,6 @@ impl<'tcx> InferCtxt<'tcx> {
             .collect()
     }
 
-    // FIXME(-Znext-solver): Get rid of this method, it's never correct. Either that,
-    // or we need to process the obligations.
-    pub fn can_eq_shallow<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool
-    where
-        T: at::ToTrace<'tcx>,
-    {
-        let origin = &ObligationCause::dummy();
-        // We're only answering whether the types could be the same, and with
-        // opaque types, "they can be the same", via registering a hidden type.
-        self.probe(|_| self.at(origin, param_env).eq(DefineOpaqueTypes::Yes, a, b).is_ok())
-    }
-
     #[instrument(skip(self), level = "debug")]
     pub fn sub_regions(
         &self,
diff --git a/compiler/rustc_mir_build/src/check_unsafety.rs b/compiler/rustc_mir_build/src/check_unsafety.rs
index bff4d6af4aa..6309f2ac98e 100644
--- a/compiler/rustc_mir_build/src/check_unsafety.rs
+++ b/compiler/rustc_mir_build/src/check_unsafety.rs
@@ -466,6 +466,24 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                     }
                 }
             }
+            ExprKind::AddressOf { arg, .. } => {
+                if let ExprKind::Scope { value: arg, .. } = self.thir[arg].kind
+                // THIR desugars UNSAFE_STATIC into *UNSAFE_STATIC_REF, where
+                // UNSAFE_STATIC_REF holds the addr of the UNSAFE_STATIC, so: take two steps
+                    && let ExprKind::Deref { arg } = self.thir[arg].kind
+                    // FIXME(workingjubiee): we lack a clear reason to reject ThreadLocalRef here,
+                    // but we also have no conclusive reason to allow it either!
+                    && let ExprKind::StaticRef { .. } = self.thir[arg].kind
+                {
+                    // A raw ref to a place expr, even an "unsafe static", is okay!
+                    // We short-circuit to not recursively traverse this expression.
+                    return;
+                    // note: const_mut_refs enables this code, and it currently remains unsafe:
+                    // static mut BYTE: u8 = 0;
+                    // static mut BYTE_PTR: *mut u8 = unsafe { addr_of_mut!(BYTE) };
+                    // static mut DEREF_BYTE_PTR: *mut u8 = unsafe { addr_of_mut!(*BYTE_PTR) };
+                }
+            }
             ExprKind::Deref { arg } => {
                 if let ExprKind::StaticRef { def_id, .. } | ExprKind::ThreadLocalRef(def_id) =
                     self.thir[arg].kind
diff --git a/compiler/rustc_mir_build/src/thir/cx/expr.rs b/compiler/rustc_mir_build/src/thir/cx/expr.rs
index 28f9300b97a..99afb500e0b 100644
--- a/compiler/rustc_mir_build/src/thir/cx/expr.rs
+++ b/compiler/rustc_mir_build/src/thir/cx/expr.rs
@@ -939,9 +939,11 @@ impl<'tcx> Cx<'tcx> {
                 }
             }
 
-            // We encode uses of statics as a `*&STATIC` where the `&STATIC` part is
-            // a constant reference (or constant raw pointer for `static mut`) in MIR
+            // A source Rust `path::to::STATIC` is a place expr like *&ident is.
+            // In THIR, we make them exactly equivalent by inserting the implied *& or *&raw,
+            // but distinguish between &STATIC and &THREAD_LOCAL as they have different semantics
             Res::Def(DefKind::Static { .. }, id) => {
+                // this is &raw for extern static or static mut, and & for other statics
                 let ty = self.tcx.static_ptr_ty(id);
                 let temp_lifetime = self
                     .rvalue_scopes
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
index 1ff2fca83fa..f9110cfb3b9 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
@@ -12,6 +12,7 @@ use rustc_middle::{
 use rustc_span::{def_id::DefId, sym, BytePos, Span, Symbol};
 
 use crate::error_reporting::TypeErrCtxt;
+use crate::infer::InferCtxtExt;
 
 impl<'tcx> TypeErrCtxt<'_, 'tcx> {
     pub fn note_and_explain_type_err(
@@ -821,7 +822,7 @@ fn foo(&self) -> Self::T { String::new() }
                                 tcx.defaultness(item.id.owner_id)
                             {
                                 let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
-                                if self.infcx.can_eq_shallow(param_env, assoc_ty, found) {
+                                if self.infcx.can_eq(param_env, assoc_ty, found) {
                                     diag.span_label(
                                         item.span,
                                         "associated type defaults can't be assumed inside the \
@@ -844,7 +845,7 @@ fn foo(&self) -> Self::T { String::new() }
                         let assoc_ty = tcx.type_of(item.id.owner_id).instantiate_identity();
                         if let hir::Defaultness::Default { has_value: true } =
                             tcx.defaultness(item.id.owner_id)
-                            && self.infcx.can_eq_shallow(param_env, assoc_ty, found)
+                            && self.infcx.can_eq(param_env, assoc_ty, found)
                         {
                             diag.span_label(
                                 item.span,
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
index 85b37ff3260..a7ea308a818 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -1,7 +1,6 @@
 use super::on_unimplemented::{AppendConstMessage, OnUnimplementedNote};
 use super::suggestions::get_explanation_based_on_obligation;
 use crate::error_reporting::infer::TyCategory;
-use crate::error_reporting::traits::infer_ctxt_ext::InferCtxtExt;
 use crate::error_reporting::traits::report_object_safety_error;
 use crate::error_reporting::TypeErrCtxt;
 use crate::errors::{
@@ -2602,7 +2601,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     })
                     .unwrap_or((found_span, None, found));
 
-                self.infcx.report_arg_count_mismatch(
+                self.report_arg_count_mismatch(
                     span,
                     closure_span,
                     expected,
@@ -2614,6 +2613,238 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         )
     }
 
+    /// Given some node representing a fn-like thing in the HIR map,
+    /// returns a span and `ArgKind` information that describes the
+    /// arguments it expects. This can be supplied to
+    /// `report_arg_count_mismatch`.
+    pub fn get_fn_like_arguments(
+        &self,
+        node: Node<'_>,
+    ) -> Option<(Span, Option<Span>, Vec<ArgKind>)> {
+        let sm = self.tcx.sess.source_map();
+        let hir = self.tcx.hir();
+        Some(match node {
+            Node::Expr(&hir::Expr {
+                kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, fn_arg_span, .. }),
+                ..
+            }) => (
+                fn_decl_span,
+                fn_arg_span,
+                hir.body(body)
+                    .params
+                    .iter()
+                    .map(|arg| {
+                        if let hir::Pat { kind: hir::PatKind::Tuple(args, _), span, .. } = *arg.pat
+                        {
+                            Some(ArgKind::Tuple(
+                                Some(span),
+                                args.iter()
+                                    .map(|pat| {
+                                        sm.span_to_snippet(pat.span)
+                                            .ok()
+                                            .map(|snippet| (snippet, "_".to_owned()))
+                                    })
+                                    .collect::<Option<Vec<_>>>()?,
+                            ))
+                        } else {
+                            let name = sm.span_to_snippet(arg.pat.span).ok()?;
+                            Some(ArgKind::Arg(name, "_".to_owned()))
+                        }
+                    })
+                    .collect::<Option<Vec<ArgKind>>>()?,
+            ),
+            Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
+            | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
+            | Node::TraitItem(&hir::TraitItem {
+                kind: hir::TraitItemKind::Fn(ref sig, _), ..
+            }) => (
+                sig.span,
+                None,
+                sig.decl
+                    .inputs
+                    .iter()
+                    .map(|arg| match arg.kind {
+                        hir::TyKind::Tup(tys) => ArgKind::Tuple(
+                            Some(arg.span),
+                            vec![("_".to_owned(), "_".to_owned()); tys.len()],
+                        ),
+                        _ => ArgKind::empty(),
+                    })
+                    .collect::<Vec<ArgKind>>(),
+            ),
+            Node::Ctor(variant_data) => {
+                let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
+                (span, None, vec![ArgKind::empty(); variant_data.fields().len()])
+            }
+            _ => panic!("non-FnLike node found: {node:?}"),
+        })
+    }
+
+    /// Reports an error when the number of arguments needed by a
+    /// trait match doesn't match the number that the expression
+    /// provides.
+    pub fn report_arg_count_mismatch(
+        &self,
+        span: Span,
+        found_span: Option<Span>,
+        expected_args: Vec<ArgKind>,
+        found_args: Vec<ArgKind>,
+        is_closure: bool,
+        closure_arg_span: Option<Span>,
+    ) -> Diag<'a> {
+        let kind = if is_closure { "closure" } else { "function" };
+
+        let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
+            let arg_length = arguments.len();
+            let distinct = matches!(other, &[ArgKind::Tuple(..)]);
+            match (arg_length, arguments.get(0)) {
+                (1, Some(ArgKind::Tuple(_, fields))) => {
+                    format!("a single {}-tuple as argument", fields.len())
+                }
+                _ => format!(
+                    "{} {}argument{}",
+                    arg_length,
+                    if distinct && arg_length > 1 { "distinct " } else { "" },
+                    pluralize!(arg_length)
+                ),
+            }
+        };
+
+        let expected_str = args_str(&expected_args, &found_args);
+        let found_str = args_str(&found_args, &expected_args);
+
+        let mut err = struct_span_code_err!(
+            self.dcx(),
+            span,
+            E0593,
+            "{} is expected to take {}, but it takes {}",
+            kind,
+            expected_str,
+            found_str,
+        );
+
+        err.span_label(span, format!("expected {kind} that takes {expected_str}"));
+
+        if let Some(found_span) = found_span {
+            err.span_label(found_span, format!("takes {found_str}"));
+
+            // Suggest to take and ignore the arguments with expected_args_length `_`s if
+            // found arguments is empty (assume the user just wants to ignore args in this case).
+            // For example, if `expected_args_length` is 2, suggest `|_, _|`.
+            if found_args.is_empty() && is_closure {
+                let underscores = vec!["_"; expected_args.len()].join(", ");
+                err.span_suggestion_verbose(
+                    closure_arg_span.unwrap_or(found_span),
+                    format!(
+                        "consider changing the closure to take and ignore the expected argument{}",
+                        pluralize!(expected_args.len())
+                    ),
+                    format!("|{underscores}|"),
+                    Applicability::MachineApplicable,
+                );
+            }
+
+            if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
+                if fields.len() == expected_args.len() {
+                    let sugg = fields
+                        .iter()
+                        .map(|(name, _)| name.to_owned())
+                        .collect::<Vec<String>>()
+                        .join(", ");
+                    err.span_suggestion_verbose(
+                        found_span,
+                        "change the closure to take multiple arguments instead of a single tuple",
+                        format!("|{sugg}|"),
+                        Applicability::MachineApplicable,
+                    );
+                }
+            }
+            if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
+                && fields.len() == found_args.len()
+                && is_closure
+            {
+                let sugg = format!(
+                    "|({}){}|",
+                    found_args
+                        .iter()
+                        .map(|arg| match arg {
+                            ArgKind::Arg(name, _) => name.to_owned(),
+                            _ => "_".to_owned(),
+                        })
+                        .collect::<Vec<String>>()
+                        .join(", "),
+                    // add type annotations if available
+                    if found_args.iter().any(|arg| match arg {
+                        ArgKind::Arg(_, ty) => ty != "_",
+                        _ => false,
+                    }) {
+                        format!(
+                            ": ({})",
+                            fields
+                                .iter()
+                                .map(|(_, ty)| ty.to_owned())
+                                .collect::<Vec<String>>()
+                                .join(", ")
+                        )
+                    } else {
+                        String::new()
+                    },
+                );
+                err.span_suggestion_verbose(
+                    found_span,
+                    "change the closure to accept a tuple instead of individual arguments",
+                    sugg,
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+
+        err
+    }
+
+    /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
+    /// in that order, and returns the generic type corresponding to the
+    /// argument of that trait (corresponding to the closure arguments).
+    pub fn type_implements_fn_trait(
+        &self,
+        param_env: ty::ParamEnv<'tcx>,
+        ty: ty::Binder<'tcx, Ty<'tcx>>,
+        polarity: ty::PredicatePolarity,
+    ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
+        self.commit_if_ok(|_| {
+            for trait_def_id in [
+                self.tcx.lang_items().fn_trait(),
+                self.tcx.lang_items().fn_mut_trait(),
+                self.tcx.lang_items().fn_once_trait(),
+            ] {
+                let Some(trait_def_id) = trait_def_id else { continue };
+                // Make a fresh inference variable so we can determine what the generic parameters
+                // of the trait are.
+                let var = self.next_ty_var(DUMMY_SP);
+                // FIXME(effects)
+                let trait_ref = ty::TraitRef::new(self.tcx, trait_def_id, [ty.skip_binder(), var]);
+                let obligation = Obligation::new(
+                    self.tcx,
+                    ObligationCause::dummy(),
+                    param_env,
+                    ty.rebind(ty::TraitPredicate { trait_ref, polarity }),
+                );
+                let ocx = ObligationCtxt::new(self);
+                ocx.register_obligation(obligation);
+                if ocx.select_all_or_error().is_empty() {
+                    return Ok((
+                        self.tcx
+                            .fn_trait_kind_from_def_id(trait_def_id)
+                            .expect("expected to map DefId to ClosureKind"),
+                        ty.rebind(self.resolve_vars_if_possible(var)),
+                    ));
+                }
+            }
+
+            Err(())
+        })
+    }
+
     fn report_not_const_evaluatable_error(
         &self,
         obligation: &PredicateObligation<'tcx>,
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/infer_ctxt_ext.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/infer_ctxt_ext.rs
deleted file mode 100644
index e8d7e80ac56..00000000000
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/infer_ctxt_ext.rs
+++ /dev/null
@@ -1,244 +0,0 @@
-// FIXME(error_reporting): This should be made into private methods on `TypeErrCtxt`.
-
-use crate::infer::InferCtxt;
-use crate::traits::{Obligation, ObligationCause, ObligationCtxt};
-use rustc_errors::{codes::*, pluralize, struct_span_code_err, Applicability, Diag};
-use rustc_hir as hir;
-use rustc_hir::Node;
-use rustc_macros::extension;
-use rustc_middle::ty::{self, Ty};
-use rustc_span::{Span, DUMMY_SP};
-
-use super::ArgKind;
-
-#[extension(pub trait InferCtxtExt<'tcx>)]
-impl<'tcx> InferCtxt<'tcx> {
-    /// Given some node representing a fn-like thing in the HIR map,
-    /// returns a span and `ArgKind` information that describes the
-    /// arguments it expects. This can be supplied to
-    /// `report_arg_count_mismatch`.
-    fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)> {
-        let sm = self.tcx.sess.source_map();
-        let hir = self.tcx.hir();
-        Some(match node {
-            Node::Expr(&hir::Expr {
-                kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, fn_arg_span, .. }),
-                ..
-            }) => (
-                fn_decl_span,
-                fn_arg_span,
-                hir.body(body)
-                    .params
-                    .iter()
-                    .map(|arg| {
-                        if let hir::Pat { kind: hir::PatKind::Tuple(args, _), span, .. } = *arg.pat
-                        {
-                            Some(ArgKind::Tuple(
-                                Some(span),
-                                args.iter()
-                                    .map(|pat| {
-                                        sm.span_to_snippet(pat.span)
-                                            .ok()
-                                            .map(|snippet| (snippet, "_".to_owned()))
-                                    })
-                                    .collect::<Option<Vec<_>>>()?,
-                            ))
-                        } else {
-                            let name = sm.span_to_snippet(arg.pat.span).ok()?;
-                            Some(ArgKind::Arg(name, "_".to_owned()))
-                        }
-                    })
-                    .collect::<Option<Vec<ArgKind>>>()?,
-            ),
-            Node::Item(&hir::Item { kind: hir::ItemKind::Fn(ref sig, ..), .. })
-            | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(ref sig, _), .. })
-            | Node::TraitItem(&hir::TraitItem {
-                kind: hir::TraitItemKind::Fn(ref sig, _), ..
-            }) => (
-                sig.span,
-                None,
-                sig.decl
-                    .inputs
-                    .iter()
-                    .map(|arg| match arg.kind {
-                        hir::TyKind::Tup(tys) => ArgKind::Tuple(
-                            Some(arg.span),
-                            vec![("_".to_owned(), "_".to_owned()); tys.len()],
-                        ),
-                        _ => ArgKind::empty(),
-                    })
-                    .collect::<Vec<ArgKind>>(),
-            ),
-            Node::Ctor(variant_data) => {
-                let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
-                (span, None, vec![ArgKind::empty(); variant_data.fields().len()])
-            }
-            _ => panic!("non-FnLike node found: {node:?}"),
-        })
-    }
-
-    /// Reports an error when the number of arguments needed by a
-    /// trait match doesn't match the number that the expression
-    /// provides.
-    fn report_arg_count_mismatch(
-        &self,
-        span: Span,
-        found_span: Option<Span>,
-        expected_args: Vec<ArgKind>,
-        found_args: Vec<ArgKind>,
-        is_closure: bool,
-        closure_arg_span: Option<Span>,
-    ) -> Diag<'_> {
-        let kind = if is_closure { "closure" } else { "function" };
-
-        let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {
-            let arg_length = arguments.len();
-            let distinct = matches!(other, &[ArgKind::Tuple(..)]);
-            match (arg_length, arguments.get(0)) {
-                (1, Some(ArgKind::Tuple(_, fields))) => {
-                    format!("a single {}-tuple as argument", fields.len())
-                }
-                _ => format!(
-                    "{} {}argument{}",
-                    arg_length,
-                    if distinct && arg_length > 1 { "distinct " } else { "" },
-                    pluralize!(arg_length)
-                ),
-            }
-        };
-
-        let expected_str = args_str(&expected_args, &found_args);
-        let found_str = args_str(&found_args, &expected_args);
-
-        let mut err = struct_span_code_err!(
-            self.dcx(),
-            span,
-            E0593,
-            "{} is expected to take {}, but it takes {}",
-            kind,
-            expected_str,
-            found_str,
-        );
-
-        err.span_label(span, format!("expected {kind} that takes {expected_str}"));
-
-        if let Some(found_span) = found_span {
-            err.span_label(found_span, format!("takes {found_str}"));
-
-            // Suggest to take and ignore the arguments with expected_args_length `_`s if
-            // found arguments is empty (assume the user just wants to ignore args in this case).
-            // For example, if `expected_args_length` is 2, suggest `|_, _|`.
-            if found_args.is_empty() && is_closure {
-                let underscores = vec!["_"; expected_args.len()].join(", ");
-                err.span_suggestion_verbose(
-                    closure_arg_span.unwrap_or(found_span),
-                    format!(
-                        "consider changing the closure to take and ignore the expected argument{}",
-                        pluralize!(expected_args.len())
-                    ),
-                    format!("|{underscores}|"),
-                    Applicability::MachineApplicable,
-                );
-            }
-
-            if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
-                if fields.len() == expected_args.len() {
-                    let sugg = fields
-                        .iter()
-                        .map(|(name, _)| name.to_owned())
-                        .collect::<Vec<String>>()
-                        .join(", ");
-                    err.span_suggestion_verbose(
-                        found_span,
-                        "change the closure to take multiple arguments instead of a single tuple",
-                        format!("|{sugg}|"),
-                        Applicability::MachineApplicable,
-                    );
-                }
-            }
-            if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..]
-                && fields.len() == found_args.len()
-                && is_closure
-            {
-                let sugg = format!(
-                    "|({}){}|",
-                    found_args
-                        .iter()
-                        .map(|arg| match arg {
-                            ArgKind::Arg(name, _) => name.to_owned(),
-                            _ => "_".to_owned(),
-                        })
-                        .collect::<Vec<String>>()
-                        .join(", "),
-                    // add type annotations if available
-                    if found_args.iter().any(|arg| match arg {
-                        ArgKind::Arg(_, ty) => ty != "_",
-                        _ => false,
-                    }) {
-                        format!(
-                            ": ({})",
-                            fields
-                                .iter()
-                                .map(|(_, ty)| ty.to_owned())
-                                .collect::<Vec<String>>()
-                                .join(", ")
-                        )
-                    } else {
-                        String::new()
-                    },
-                );
-                err.span_suggestion_verbose(
-                    found_span,
-                    "change the closure to accept a tuple instead of individual arguments",
-                    sugg,
-                    Applicability::MachineApplicable,
-                );
-            }
-        }
-
-        err
-    }
-
-    /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
-    /// in that order, and returns the generic type corresponding to the
-    /// argument of that trait (corresponding to the closure arguments).
-    fn type_implements_fn_trait(
-        &self,
-        param_env: ty::ParamEnv<'tcx>,
-        ty: ty::Binder<'tcx, Ty<'tcx>>,
-        polarity: ty::PredicatePolarity,
-    ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()> {
-        self.commit_if_ok(|_| {
-            for trait_def_id in [
-                self.tcx.lang_items().fn_trait(),
-                self.tcx.lang_items().fn_mut_trait(),
-                self.tcx.lang_items().fn_once_trait(),
-            ] {
-                let Some(trait_def_id) = trait_def_id else { continue };
-                // Make a fresh inference variable so we can determine what the generic parameters
-                // of the trait are.
-                let var = self.next_ty_var(DUMMY_SP);
-                // FIXME(effects)
-                let trait_ref = ty::TraitRef::new(self.tcx, trait_def_id, [ty.skip_binder(), var]);
-                let obligation = Obligation::new(
-                    self.tcx,
-                    ObligationCause::dummy(),
-                    param_env,
-                    ty.rebind(ty::TraitPredicate { trait_ref, polarity }),
-                );
-                let ocx = ObligationCtxt::new(self);
-                ocx.register_obligation(obligation);
-                if ocx.select_all_or_error().is_empty() {
-                    return Ok((
-                        self.tcx
-                            .fn_trait_kind_from_def_id(trait_def_id)
-                            .expect("expected to map DefId to ClosureKind"),
-                        ty.rebind(self.resolve_vars_if_possible(var)),
-                    ));
-                }
-            }
-
-            Err(())
-        })
-    }
-}
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
index 10624786bae..87fdc5ddff8 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
@@ -1,6 +1,5 @@
 pub mod ambiguity;
 mod fulfillment_errors;
-mod infer_ctxt_ext;
 pub mod on_unimplemented;
 mod overflow;
 pub mod suggestions;
@@ -23,7 +22,6 @@ use rustc_span::{ErrorGuaranteed, ExpnKind, Span};
 use crate::error_reporting::TypeErrCtxt;
 use crate::traits::{FulfillmentError, FulfillmentErrorCode};
 
-pub use self::infer_ctxt_ext::*;
 pub use self::overflow::*;
 
 // When outputting impl candidates, prefer showing those that are more similar.