Move some utils to ty_utils

3 files changed, 322 insertions, 300 deletions

diff --git a/clippy_utils/src/eager_or_lazy.rs b/clippy_utils/src/eager_or_lazy.rs
index 8013c4e4fcb..88b115a63d7 100644
--- a/clippy_utils/src/eager_or_lazy.rs
+++ b/clippy_utils/src/eager_or_lazy.rs
@@ -9,7 +9,8 @@
 //!  - or-fun-call
 //!  - option-if-let-else
 
-use crate::{is_ctor_or_promotable_const_function, is_type_diagnostic_item};
+use crate::is_ctor_or_promotable_const_function;
+use crate::ty::is_type_diagnostic_item;
 use rustc_hir::def::{DefKind, Res};
 
 use rustc_hir::intravisit;
diff --git a/clippy_utils/src/lib.rs b/clippy_utils/src/lib.rs
index 5b2529b4930..366962d8b77 100644
--- a/clippy_utils/src/lib.rs
+++ b/clippy_utils/src/lib.rs
@@ -42,6 +42,7 @@ pub mod paths;
 pub mod ptr;
 pub mod qualify_min_const_fn;
 pub mod sugg;
+pub mod ty;
 pub mod usage;
 pub mod visitors;
 
@@ -54,7 +55,7 @@ use std::collections::hash_map::Entry;
 use std::hash::BuildHasherDefault;
 
 use if_chain::if_chain;
-use rustc_ast::ast::{self, Attribute, BorrowKind, LitKind, Mutability};
+use rustc_ast::ast::{self, Attribute, BorrowKind, LitKind};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
@@ -65,14 +66,13 @@ use rustc_hir::{
     def, Arm, BindingAnnotation, Block, Body, Constness, CrateItem, Expr, ExprKind, FnDecl, ForeignItem, GenericArgs,
     GenericParam, HirId, Impl, ImplItem, ImplItemKind, Item, ItemKind, LangItem, Lifetime, Local, MacroDef,
     MatchSource, Node, Param, Pat, PatKind, Path, PathSegment, QPath, Stmt, StructField, TraitItem, TraitItemKind,
-    TraitRef, TyKind, Unsafety, Variant, Visibility,
+    TraitRef, TyKind, Variant, Visibility,
 };
-use rustc_infer::infer::TyCtxtInferExt;
 use rustc_lint::{LateContext, Level, Lint, LintContext};
 use rustc_middle::hir::exports::Export;
 use rustc_middle::hir::map::Map;
-use rustc_middle::ty::subst::{GenericArg, GenericArgKind};
-use rustc_middle::ty::{self, layout::IntegerExt, DefIdTree, IntTy, Ty, TyCtxt, TypeFoldable, UintTy};
+use rustc_middle::ty as rustc_ty;
+use rustc_middle::ty::{layout::IntegerExt, DefIdTree, Ty, TyCtxt, TypeFoldable};
 use rustc_semver::RustcVersion;
 use rustc_session::Session;
 use rustc_span::hygiene::{self, ExpnKind, MacroKind};
@@ -81,11 +81,10 @@ use rustc_span::sym;
 use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_span::{BytePos, Pos, Span, SyntaxContext, DUMMY_SP};
 use rustc_target::abi::Integer;
-use rustc_trait_selection::traits::query::normalize::AtExt;
 use smallvec::SmallVec;
 
 use crate::consts::{constant, Constant};
-use std::collections::HashMap;
+use crate::ty::is_recursively_primitive_type;
 
 pub fn parse_msrv(msrv: &str, sess: Option<&Session>, span: Option<Span>) -> Option<RustcVersion> {
     if let Ok(version) = RustcVersion::parse(msrv) {
@@ -256,35 +255,6 @@ pub fn is_wild<'tcx>(pat: &impl std::ops::Deref<Target = Pat<'tcx>>) -> bool {
     matches!(pat.kind, PatKind::Wild)
 }
 
-/// Checks if type is struct, enum or union type with the given def path.
-///
-/// If the type is a diagnostic item, use `is_type_diagnostic_item` instead.
-/// If you change the signature, remember to update the internal lint `MatchTypeOnDiagItem`
-pub fn match_type(cx: &LateContext<'_>, ty: Ty<'_>, path: &[&str]) -> bool {
-    match ty.kind() {
-        ty::Adt(adt, _) => match_def_path(cx, adt.did, path),
-        _ => false,
-    }
-}
-
-/// Checks if the type is equal to a diagnostic item
-///
-/// If you change the signature, remember to update the internal lint `MatchTypeOnDiagItem`
-pub fn is_type_diagnostic_item(cx: &LateContext<'_>, ty: Ty<'_>, diag_item: Symbol) -> bool {
-    match ty.kind() {
-        ty::Adt(adt, _) => cx.tcx.is_diagnostic_item(diag_item, adt.did),
-        _ => false,
-    }
-}
-
-/// Checks if the type is equal to a lang item
-pub fn is_type_lang_item(cx: &LateContext<'_>, ty: Ty<'_>, lang_item: hir::LangItem) -> bool {
-    match ty.kind() {
-        ty::Adt(adt, _) => cx.tcx.lang_items().require(lang_item).unwrap() == adt.did,
-        _ => false,
-    }
-}
-
 /// Checks if the first type parameter is a lang item.
 pub fn is_ty_param_lang_item(cx: &LateContext<'_>, qpath: &QPath<'tcx>, item: LangItem) -> Option<&'tcx hir::Ty<'tcx>> {
     let ty = get_qpath_generic_tys(qpath).next()?;
@@ -319,11 +289,6 @@ pub fn is_ty_param_diagnostic_item(
     }
 }
 
-/// Return `true` if the passed `typ` is `isize` or `usize`.
-pub fn is_isize_or_usize(typ: Ty<'_>) -> bool {
-    matches!(typ.kind(), ty::Int(IntTy::Isize) | ty::Uint(UintTy::Usize))
-}
-
 /// Checks if the method call given in `expr` belongs to the given trait.
 /// This is a deprecated function, consider using [`is_trait_method`].
 pub fn match_trait_method(cx: &LateContext<'_>, expr: &Expr<'_>, path: &[&str]) -> bool {
@@ -338,10 +303,10 @@ pub fn is_diagnostic_assoc_item(cx: &LateContext<'_>, def_id: DefId, diag_item:
     cx.tcx
         .opt_associated_item(def_id)
         .and_then(|associated_item| match associated_item.container {
-            ty::TraitContainer(assoc_def_id) => Some(assoc_def_id),
-            ty::ImplContainer(assoc_def_id) => match cx.tcx.type_of(assoc_def_id).kind() {
-                ty::Adt(adt, _) => Some(adt.did),
-                ty::Slice(_) => cx.tcx.get_diagnostic_item(sym::slice), // this isn't perfect but it works
+            rustc_ty::TraitContainer(assoc_def_id) => Some(assoc_def_id),
+            rustc_ty::ImplContainer(assoc_def_id) => match cx.tcx.type_of(assoc_def_id).kind() {
+                rustc_ty::Adt(adt, _) => Some(adt.did),
+                rustc_ty::Slice(_) => cx.tcx.get_diagnostic_item(sym::slice), // this isn't perfect but it works
                 _ => None,
             },
         })
@@ -540,26 +505,6 @@ pub fn get_trait_def_id(cx: &LateContext<'_>, path: &[&str]) -> Option<DefId> {
     }
 }
 
-/// Checks whether a type implements a trait.
-/// See also `get_trait_def_id`.
-pub fn implements_trait<'tcx>(
-    cx: &LateContext<'tcx>,
-    ty: Ty<'tcx>,
-    trait_id: DefId,
-    ty_params: &[GenericArg<'tcx>],
-) -> bool {
-    // Do not check on infer_types to avoid panic in evaluate_obligation.
-    if ty.has_infer_types() {
-        return false;
-    }
-    let ty = cx.tcx.erase_regions(ty);
-    if ty.has_escaping_bound_vars() {
-        return false;
-    }
-    let ty_params = cx.tcx.mk_substs(ty_params.iter());
-    cx.tcx.type_implements_trait((trait_id, ty, ty_params, cx.param_env))
-}
-
 /// Gets the `hir::TraitRef` of the trait the given method is implemented for.
 ///
 /// Use this if you want to find the `TraitRef` of the `Add` trait in this example:
@@ -587,26 +532,6 @@ pub fn trait_ref_of_method<'tcx>(cx: &LateContext<'tcx>, hir_id: HirId) -> Optio
     None
 }
 
-/// Checks whether this type implements `Drop`.
-pub fn has_drop<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
-    match ty.ty_adt_def() {
-        Some(def) => def.has_dtor(cx.tcx),
-        None => false,
-    }
-}
-
-/// Checks whether a type can be partially moved.
-pub fn can_partially_move_ty(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
-    if has_drop(cx, ty) || is_copy(cx, ty) {
-        return false;
-    }
-    match ty.kind() {
-        ty::Param(_) => false,
-        ty::Adt(def, subs) => def.all_fields().any(|f| !is_copy(cx, f.ty(cx.tcx, subs))),
-        _ => true,
-    }
-}
-
 /// Returns the method names and argument list of nested method call expressions that make up
 /// `expr`. method/span lists are sorted with the most recent call first.
 pub fn method_calls<'tcx>(
@@ -1155,26 +1080,6 @@ pub fn get_parent_as_impl(tcx: TyCtxt<'_>, id: HirId) -> Option<&Impl<'_>> {
     }
 }
 
-/// Returns the base type for HIR references and pointers.
-pub fn walk_ptrs_hir_ty<'tcx>(ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
-    match ty.kind {
-        TyKind::Ptr(ref mut_ty) | TyKind::Rptr(_, ref mut_ty) => walk_ptrs_hir_ty(&mut_ty.ty),
-        _ => ty,
-    }
-}
-
-/// Returns the base type for references and raw pointers, and count reference
-/// depth.
-pub fn walk_ptrs_ty_depth(ty: Ty<'_>) -> (Ty<'_>, usize) {
-    fn inner(ty: Ty<'_>, depth: usize) -> (Ty<'_>, usize) {
-        match ty.kind() {
-            ty::Ref(_, ty, _) => inner(ty, depth + 1),
-            _ => (ty, depth),
-        }
-    }
-    inner(ty, 0)
-}
-
 /// Checks whether the given expression is a constant integer of the given value.
 /// unlike `is_integer_literal`, this version does const folding
 pub fn is_integer_const(cx: &LateContext<'_>, e: &Expr<'_>, value: u128) -> bool {
@@ -1270,26 +1175,6 @@ pub fn return_ty<'tcx>(cx: &LateContext<'tcx>, fn_item: hir::HirId) -> Ty<'tcx>
     cx.tcx.erase_late_bound_regions(ret_ty)
 }
 
-/// Walks into `ty` and returns `true` if any inner type is the same as `other_ty`
-pub fn contains_ty(ty: Ty<'_>, other_ty: Ty<'_>) -> bool {
-    ty.walk().any(|inner| match inner.unpack() {
-        GenericArgKind::Type(inner_ty) => ty::TyS::same_type(other_ty, inner_ty),
-        GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
-    })
-}
-
-/// Returns `true` if the given type is an `unsafe` function.
-pub fn type_is_unsafe_function<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
-    match ty.kind() {
-        ty::FnDef(..) | ty::FnPtr(_) => ty.fn_sig(cx.tcx).unsafety() == Unsafety::Unsafe,
-        _ => false,
-    }
-}
-
-pub fn is_copy<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
-    ty.is_copy_modulo_regions(cx.tcx.at(DUMMY_SP), cx.param_env)
-}
-
 /// Checks if an expression is constructing a tuple-like enum variant or struct
 pub fn is_ctor_or_promotable_const_function(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     if let ExprKind::Call(ref fun, _) = expr.kind {
@@ -1338,11 +1223,13 @@ pub fn is_refutable(cx: &LateContext<'_>, pat: &Pat<'_>) -> bool {
         },
         PatKind::Slice(ref head, ref middle, ref tail) => {
             match &cx.typeck_results().node_type(pat.hir_id).kind() {
-                ty::Slice(..) => {
+                rustc_ty::Slice(..) => {
                     // [..] is the only irrefutable slice pattern.
                     !head.is_empty() || middle.is_none() || !tail.is_empty()
                 },
-                ty::Array(..) => are_refutable(cx, head.iter().chain(middle).chain(tail.iter()).map(|pat| &**pat)),
+                rustc_ty::Array(..) => {
+                    are_refutable(cx, head.iter().chain(middle).chain(tail.iter()).map(|pat| &**pat))
+                },
                 _ => {
                     // unreachable!()
                     true
@@ -1454,26 +1341,26 @@ pub fn strip_pat_refs<'hir>(mut pat: &'hir Pat<'hir>) -> &'hir Pat<'hir> {
     pat
 }
 
-pub fn int_bits(tcx: TyCtxt<'_>, ity: ty::IntTy) -> u64 {
+pub fn int_bits(tcx: TyCtxt<'_>, ity: rustc_ty::IntTy) -> u64 {
     Integer::from_int_ty(&tcx, ity).size().bits()
 }
 
 #[allow(clippy::cast_possible_wrap)]
 /// Turn a constant int byte representation into an i128
-pub fn sext(tcx: TyCtxt<'_>, u: u128, ity: ty::IntTy) -> i128 {
+pub fn sext(tcx: TyCtxt<'_>, u: u128, ity: rustc_ty::IntTy) -> i128 {
     let amt = 128 - int_bits(tcx, ity);
     ((u as i128) << amt) >> amt
 }
 
 #[allow(clippy::cast_sign_loss)]
 /// clip unused bytes
-pub fn unsext(tcx: TyCtxt<'_>, u: i128, ity: ty::IntTy) -> u128 {
+pub fn unsext(tcx: TyCtxt<'_>, u: i128, ity: rustc_ty::IntTy) -> u128 {
     let amt = 128 - int_bits(tcx, ity);
     ((u as u128) << amt) >> amt
 }
 
 /// clip unused bytes
-pub fn clip(tcx: TyCtxt<'_>, u: u128, ity: ty::UintTy) -> u128 {
+pub fn clip(tcx: TyCtxt<'_>, u: u128, ity: rustc_ty::UintTy) -> u128 {
     let bits = Integer::from_uint_ty(&tcx, ity).size().bits();
     let amt = 128 - bits;
     (u << amt) >> amt
@@ -1526,47 +1413,6 @@ pub fn any_parent_is_automatically_derived(tcx: TyCtxt<'_>, node: HirId) -> bool
     false
 }
 
-/// Returns true if ty has `iter` or `iter_mut` methods
-pub fn has_iter_method(cx: &LateContext<'_>, probably_ref_ty: Ty<'_>) -> Option<Symbol> {
-    // FIXME: instead of this hard-coded list, we should check if `<adt>::iter`
-    // exists and has the desired signature. Unfortunately FnCtxt is not exported
-    // so we can't use its `lookup_method` method.
-    let into_iter_collections: &[Symbol] = &[
-        sym::vec_type,
-        sym::option_type,
-        sym::result_type,
-        sym::BTreeMap,
-        sym::BTreeSet,
-        sym::vecdeque_type,
-        sym::LinkedList,
-        sym::BinaryHeap,
-        sym::hashset_type,
-        sym::hashmap_type,
-        sym::PathBuf,
-        sym::Path,
-        sym::Receiver,
-    ];
-
-    let ty_to_check = match probably_ref_ty.kind() {
-        ty::Ref(_, ty_to_check, _) => ty_to_check,
-        _ => probably_ref_ty,
-    };
-
-    let def_id = match ty_to_check.kind() {
-        ty::Array(..) => return Some(sym::array),
-        ty::Slice(..) => return Some(sym::slice),
-        ty::Adt(adt, _) => adt.did,
-        _ => return None,
-    };
-
-    for &name in into_iter_collections {
-        if cx.tcx.is_diagnostic_item(name, def_id) {
-            return Some(cx.tcx.item_name(def_id));
-        }
-    }
-    None
-}
-
 /// Matches a function call with the given path and returns the arguments.
 ///
 /// Usage:
@@ -1591,51 +1437,6 @@ pub fn match_function_call<'tcx>(
     None
 }
 
-// FIXME: Per https://doc.rust-lang.org/nightly/nightly-rustc/rustc_trait_selection/infer/at/struct.At.html#method.normalize
-// this function can be removed once the `normalizie` method does not panic when normalization does
-// not succeed
-/// Checks if `Ty` is normalizable. This function is useful
-/// to avoid crashes on `layout_of`.
-pub fn is_normalizable<'tcx>(cx: &LateContext<'tcx>, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
-    is_normalizable_helper(cx, param_env, ty, &mut HashMap::new())
-}
-
-fn is_normalizable_helper<'tcx>(
-    cx: &LateContext<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    ty: Ty<'tcx>,
-    cache: &mut HashMap<Ty<'tcx>, bool>,
-) -> bool {
-    if let Some(&cached_result) = cache.get(ty) {
-        return cached_result;
-    }
-    // prevent recursive loops, false-negative is better than endless loop leading to stack overflow
-    cache.insert(ty, false);
-    let result = cx.tcx.infer_ctxt().enter(|infcx| {
-        let cause = rustc_middle::traits::ObligationCause::dummy();
-        if infcx.at(&cause, param_env).normalize(ty).is_ok() {
-            match ty.kind() {
-                ty::Adt(def, substs) => def.variants.iter().all(|variant| {
-                    variant
-                        .fields
-                        .iter()
-                        .all(|field| is_normalizable_helper(cx, param_env, field.ty(cx.tcx, substs), cache))
-                }),
-                _ => ty.walk().all(|generic_arg| match generic_arg.unpack() {
-                    GenericArgKind::Type(inner_ty) if inner_ty != ty => {
-                        is_normalizable_helper(cx, param_env, inner_ty, cache)
-                    },
-                    _ => true, // if inner_ty == ty, we've already checked it
-                }),
-            }
-        } else {
-            false
-        }
-    });
-    cache.insert(ty, result);
-    result
-}
-
 pub fn match_def_path<'tcx>(cx: &LateContext<'tcx>, did: DefId, syms: &[&str]) -> bool {
     // We have to convert `syms` to `&[Symbol]` here because rustc's `match_def_path`
     // accepts only that. We should probably move to Symbols in Clippy as well.
@@ -1721,44 +1522,6 @@ pub fn must_use_attr(attrs: &[Attribute]) -> Option<&Attribute> {
     attr_by_name(attrs, "must_use")
 }
 
-// Returns whether the type has #[must_use] attribute
-pub fn is_must_use_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
-    match ty.kind() {
-        ty::Adt(ref adt, _) => must_use_attr(&cx.tcx.get_attrs(adt.did)).is_some(),
-        ty::Foreign(ref did) => must_use_attr(&cx.tcx.get_attrs(*did)).is_some(),
-        ty::Slice(ref ty)
-        | ty::Array(ref ty, _)
-        | ty::RawPtr(ty::TypeAndMut { ref ty, .. })
-        | ty::Ref(_, ref ty, _) => {
-            // for the Array case we don't need to care for the len == 0 case
-            // because we don't want to lint functions returning empty arrays
-            is_must_use_ty(cx, *ty)
-        },
-        ty::Tuple(ref substs) => substs.types().any(|ty| is_must_use_ty(cx, ty)),
-        ty::Opaque(ref def_id, _) => {
-            for (predicate, _) in cx.tcx.explicit_item_bounds(*def_id) {
-                if let ty::PredicateKind::Trait(trait_predicate, _) = predicate.kind().skip_binder() {
-                    if must_use_attr(&cx.tcx.get_attrs(trait_predicate.trait_ref.def_id)).is_some() {
-                        return true;
-                    }
-                }
-            }
-            false
-        },
-        ty::Dynamic(binder, _) => {
-            for predicate in binder.iter() {
-                if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate.skip_binder() {
-                    if must_use_attr(&cx.tcx.get_attrs(trait_ref.def_id)).is_some() {
-                        return true;
-                    }
-                }
-            }
-            false
-        },
-        _ => false,
-    }
-}
-
 // check if expr is calling method or function with #[must_use] attribute
 pub fn is_must_use_func_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     let did = match expr.kind {
@@ -1853,18 +1616,6 @@ pub fn run_lints(cx: &LateContext<'_>, lints: &[&'static Lint], id: HirId) -> bo
     })
 }
 
-/// Returns true iff the given type is a primitive (a bool or char, any integer or floating-point
-/// number type, a str, or an array, slice, or tuple of those types).
-pub fn is_recursively_primitive_type(ty: Ty<'_>) -> bool {
-    match ty.kind() {
-        ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str => true,
-        ty::Ref(_, inner, _) if *inner.kind() == ty::Str => true,
-        ty::Array(inner_type, _) | ty::Slice(inner_type) => is_recursively_primitive_type(inner_type),
-        ty::Tuple(inner_types) => inner_types.types().all(is_recursively_primitive_type),
-        _ => false,
-    }
-}
-
 /// Returns Option<String> where String is a textual representation of the type encapsulated in the
 /// slice iff the given expression is a slice of primitives (as defined in the
 /// `is_recursively_primitive_type` function) and None otherwise.
@@ -1872,9 +1623,9 @@ pub fn is_slice_of_primitives(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<S
     let expr_type = cx.typeck_results().expr_ty_adjusted(expr);
     let expr_kind = expr_type.kind();
     let is_primitive = match expr_kind {
-        ty::Slice(element_type) => is_recursively_primitive_type(element_type),
-        ty::Ref(_, inner_ty, _) if matches!(inner_ty.kind(), &ty::Slice(_)) => {
-            if let ty::Slice(element_type) = inner_ty.kind() {
+        rustc_ty::Slice(element_type) => is_recursively_primitive_type(element_type),
+        rustc_ty::Ref(_, inner_ty, _) if matches!(inner_ty.kind(), &rustc_ty::Slice(_)) => {
+            if let rustc_ty::Slice(element_type) = inner_ty.kind() {
                 is_recursively_primitive_type(element_type)
             } else {
                 unreachable!()
@@ -1887,9 +1638,9 @@ pub fn is_slice_of_primitives(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<S
         // if we have wrappers like Array, Slice or Tuple, print these
         // and get the type enclosed in the slice ref
         match expr_type.peel_refs().walk().nth(1).unwrap().expect_ty().kind() {
-            ty::Slice(..) => return Some("slice".into()),
-            ty::Array(..) => return Some("array".into()),
-            ty::Tuple(..) => return Some("tuple".into()),
+            rustc_ty::Slice(..) => return Some("slice".into()),
+            rustc_ty::Array(..) => return Some("array".into()),
+            rustc_ty::Tuple(..) => return Some("tuple".into()),
             _ => {
                 // is_recursively_primitive_type() should have taken care
                 // of the rest and we can rely on the type that is found
@@ -1973,32 +1724,6 @@ pub fn peel_hir_expr_refs(expr: &'a Expr<'a>) -> (&'a Expr<'a>, usize) {
     f(expr, 0)
 }
 
-/// Peels off all references on the type. Returns the underlying type and the number of references
-/// removed.
-pub fn peel_mid_ty_refs(ty: Ty<'_>) -> (Ty<'_>, usize) {
-    fn peel(ty: Ty<'_>, count: usize) -> (Ty<'_>, usize) {
-        if let ty::Ref(_, ty, _) = ty.kind() {
-            peel(ty, count + 1)
-        } else {
-            (ty, count)
-        }
-    }
-    peel(ty, 0)
-}
-
-/// Peels off all references on the type.Returns the underlying type, the number of references
-/// removed, and whether the pointer is ultimately mutable or not.
-pub fn peel_mid_ty_refs_is_mutable(ty: Ty<'_>) -> (Ty<'_>, usize, Mutability) {
-    fn f(ty: Ty<'_>, count: usize, mutability: Mutability) -> (Ty<'_>, usize, Mutability) {
-        match ty.kind() {
-            ty::Ref(_, ty, Mutability::Mut) => f(ty, count + 1, mutability),
-            ty::Ref(_, ty, Mutability::Not) => f(ty, count + 1, Mutability::Not),
-            _ => (ty, count, mutability),
-        }
-    }
-    f(ty, 0, Mutability::Mut)
-}
-
 #[macro_export]
 macro_rules! unwrap_cargo_metadata {
     ($cx: ident, $lint: ident, $deps: expr) => {{
diff --git a/clippy_utils/src/ty.rs b/clippy_utils/src/ty.rs
new file mode 100644
index 00000000000..f4a1ae67da3
--- /dev/null
+++ b/clippy_utils/src/ty.rs
@@ -0,0 +1,296 @@
+//! Util methods for [`rustc_middle::ty`]
+
+#![allow(clippy::module_name_repetitions)]
+
+use std::collections::HashMap;
+
+use rustc_ast::ast::Mutability;
+use rustc_hir as hir;
+use rustc_hir::def_id::DefId;
+use rustc_hir::{TyKind, Unsafety};
+use rustc_infer::infer::TyCtxtInferExt;
+use rustc_lint::LateContext;
+use rustc_middle::ty::subst::{GenericArg, GenericArgKind};
+use rustc_middle::ty::{self, IntTy, Ty, TypeFoldable, UintTy};
+use rustc_span::sym;
+use rustc_span::symbol::Symbol;
+use rustc_span::DUMMY_SP;
+use rustc_trait_selection::traits::query::normalize::AtExt;
+
+use crate::{match_def_path, must_use_attr};
+
+pub fn is_copy<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
+    ty.is_copy_modulo_regions(cx.tcx.at(DUMMY_SP), cx.param_env)
+}
+
+/// Checks whether a type can be partially moved.
+pub fn can_partially_move_ty(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
+    if has_drop(cx, ty) || is_copy(cx, ty) {
+        return false;
+    }
+    match ty.kind() {
+        ty::Param(_) => false,
+        ty::Adt(def, subs) => def.all_fields().any(|f| !is_copy(cx, f.ty(cx.tcx, subs))),
+        _ => true,
+    }
+}
+
+/// Walks into `ty` and returns `true` if any inner type is the same as `other_ty`
+pub fn contains_ty(ty: Ty<'_>, other_ty: Ty<'_>) -> bool {
+    ty.walk().any(|inner| match inner.unpack() {
+        GenericArgKind::Type(inner_ty) => ty::TyS::same_type(other_ty, inner_ty),
+        GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
+    })
+}
+
+/// Returns true if ty has `iter` or `iter_mut` methods
+pub fn has_iter_method(cx: &LateContext<'_>, probably_ref_ty: Ty<'_>) -> Option<Symbol> {
+    // FIXME: instead of this hard-coded list, we should check if `<adt>::iter`
+    // exists and has the desired signature. Unfortunately FnCtxt is not exported
+    // so we can't use its `lookup_method` method.
+    let into_iter_collections: &[Symbol] = &[
+        sym::vec_type,
+        sym::option_type,
+        sym::result_type,
+        sym::BTreeMap,
+        sym::BTreeSet,
+        sym::vecdeque_type,
+        sym::LinkedList,
+        sym::BinaryHeap,
+        sym::hashset_type,
+        sym::hashmap_type,
+        sym::PathBuf,
+        sym::Path,
+        sym::Receiver,
+    ];
+
+    let ty_to_check = match probably_ref_ty.kind() {
+        ty::Ref(_, ty_to_check, _) => ty_to_check,
+        _ => probably_ref_ty,
+    };
+
+    let def_id = match ty_to_check.kind() {
+        ty::Array(..) => return Some(sym::array),
+        ty::Slice(..) => return Some(sym::slice),
+        ty::Adt(adt, _) => adt.did,
+        _ => return None,
+    };
+
+    for &name in into_iter_collections {
+        if cx.tcx.is_diagnostic_item(name, def_id) {
+            return Some(cx.tcx.item_name(def_id));
+        }
+    }
+    None
+}
+
+/// Checks whether a type implements a trait.
+/// See also `get_trait_def_id`.
+pub fn implements_trait<'tcx>(
+    cx: &LateContext<'tcx>,
+    ty: Ty<'tcx>,
+    trait_id: DefId,
+    ty_params: &[GenericArg<'tcx>],
+) -> bool {
+    // Do not check on infer_types to avoid panic in evaluate_obligation.
+    if ty.has_infer_types() {
+        return false;
+    }
+    let ty = cx.tcx.erase_regions(ty);
+    if ty.has_escaping_bound_vars() {
+        return false;
+    }
+    let ty_params = cx.tcx.mk_substs(ty_params.iter());
+    cx.tcx.type_implements_trait((trait_id, ty, ty_params, cx.param_env))
+}
+
+/// Checks whether this type implements `Drop`.
+pub fn has_drop<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
+    match ty.ty_adt_def() {
+        Some(def) => def.has_dtor(cx.tcx),
+        None => false,
+    }
+}
+
+// Returns whether the type has #[must_use] attribute
+pub fn is_must_use_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
+    match ty.kind() {
+        ty::Adt(ref adt, _) => must_use_attr(&cx.tcx.get_attrs(adt.did)).is_some(),
+        ty::Foreign(ref did) => must_use_attr(&cx.tcx.get_attrs(*did)).is_some(),
+        ty::Slice(ref ty)
+        | ty::Array(ref ty, _)
+        | ty::RawPtr(ty::TypeAndMut { ref ty, .. })
+        | ty::Ref(_, ref ty, _) => {
+            // for the Array case we don't need to care for the len == 0 case
+            // because we don't want to lint functions returning empty arrays
+            is_must_use_ty(cx, *ty)
+        },
+        ty::Tuple(ref substs) => substs.types().any(|ty| is_must_use_ty(cx, ty)),
+        ty::Opaque(ref def_id, _) => {
+            for (predicate, _) in cx.tcx.explicit_item_bounds(*def_id) {
+                if let ty::PredicateKind::Trait(trait_predicate, _) = predicate.kind().skip_binder() {
+                    if must_use_attr(&cx.tcx.get_attrs(trait_predicate.trait_ref.def_id)).is_some() {
+                        return true;
+                    }
+                }
+            }
+            false
+        },
+        ty::Dynamic(binder, _) => {
+            for predicate in binder.iter() {
+                if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate.skip_binder() {
+                    if must_use_attr(&cx.tcx.get_attrs(trait_ref.def_id)).is_some() {
+                        return true;
+                    }
+                }
+            }
+            false
+        },
+        _ => false,
+    }
+}
+
+// FIXME: Per https://doc.rust-lang.org/nightly/nightly-rustc/rustc_trait_selection/infer/at/struct.At.html#method.normalize
+// this function can be removed once the `normalizie` method does not panic when normalization does
+// not succeed
+/// Checks if `Ty` is normalizable. This function is useful
+/// to avoid crashes on `layout_of`.
+pub fn is_normalizable<'tcx>(cx: &LateContext<'tcx>, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
+    is_normalizable_helper(cx, param_env, ty, &mut HashMap::new())
+}
+
+fn is_normalizable_helper<'tcx>(
+    cx: &LateContext<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    ty: Ty<'tcx>,
+    cache: &mut HashMap<Ty<'tcx>, bool>,
+) -> bool {
+    if let Some(&cached_result) = cache.get(ty) {
+        return cached_result;
+    }
+    // prevent recursive loops, false-negative is better than endless loop leading to stack overflow
+    cache.insert(ty, false);
+    let result = cx.tcx.infer_ctxt().enter(|infcx| {
+        let cause = rustc_middle::traits::ObligationCause::dummy();
+        if infcx.at(&cause, param_env).normalize(ty).is_ok() {
+            match ty.kind() {
+                ty::Adt(def, substs) => def.variants.iter().all(|variant| {
+                    variant
+                        .fields
+                        .iter()
+                        .all(|field| is_normalizable_helper(cx, param_env, field.ty(cx.tcx, substs), cache))
+                }),
+                _ => ty.walk().all(|generic_arg| match generic_arg.unpack() {
+                    GenericArgKind::Type(inner_ty) if inner_ty != ty => {
+                        is_normalizable_helper(cx, param_env, inner_ty, cache)
+                    },
+                    _ => true, // if inner_ty == ty, we've already checked it
+                }),
+            }
+        } else {
+            false
+        }
+    });
+    cache.insert(ty, result);
+    result
+}
+
+/// Returns true iff the given type is a primitive (a bool or char, any integer or floating-point
+/// number type, a str, or an array, slice, or tuple of those types).
+pub fn is_recursively_primitive_type(ty: Ty<'_>) -> bool {
+    match ty.kind() {
+        ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str => true,
+        ty::Ref(_, inner, _) if *inner.kind() == ty::Str => true,
+        ty::Array(inner_type, _) | ty::Slice(inner_type) => is_recursively_primitive_type(inner_type),
+        ty::Tuple(inner_types) => inner_types.types().all(is_recursively_primitive_type),
+        _ => false,
+    }
+}
+
+/// Checks if the type is equal to a diagnostic item
+///
+/// If you change the signature, remember to update the internal lint `MatchTypeOnDiagItem`
+pub fn is_type_diagnostic_item(cx: &LateContext<'_>, ty: Ty<'_>, diag_item: Symbol) -> bool {
+    match ty.kind() {
+        ty::Adt(adt, _) => cx.tcx.is_diagnostic_item(diag_item, adt.did),
+        _ => false,
+    }
+}
+
+/// Checks if the type is equal to a lang item
+pub fn is_type_lang_item(cx: &LateContext<'_>, ty: Ty<'_>, lang_item: hir::LangItem) -> bool {
+    match ty.kind() {
+        ty::Adt(adt, _) => cx.tcx.lang_items().require(lang_item).unwrap() == adt.did,
+        _ => false,
+    }
+}
+
+/// Return `true` if the passed `typ` is `isize` or `usize`.
+pub fn is_isize_or_usize(typ: Ty<'_>) -> bool {
+    matches!(typ.kind(), ty::Int(IntTy::Isize) | ty::Uint(UintTy::Usize))
+}
+
+/// Checks if type is struct, enum or union type with the given def path.
+///
+/// If the type is a diagnostic item, use `is_type_diagnostic_item` instead.
+/// If you change the signature, remember to update the internal lint `MatchTypeOnDiagItem`
+pub fn match_type(cx: &LateContext<'_>, ty: Ty<'_>, path: &[&str]) -> bool {
+    match ty.kind() {
+        ty::Adt(adt, _) => match_def_path(cx, adt.did, path),
+        _ => false,
+    }
+}
+
+/// Peels off all references on the type. Returns the underlying type and the number of references
+/// removed.
+pub fn peel_mid_ty_refs(ty: Ty<'_>) -> (Ty<'_>, usize) {
+    fn peel(ty: Ty<'_>, count: usize) -> (Ty<'_>, usize) {
+        if let ty::Ref(_, ty, _) = ty.kind() {
+            peel(ty, count + 1)
+        } else {
+            (ty, count)
+        }
+    }
+    peel(ty, 0)
+}
+
+/// Peels off all references on the type.Returns the underlying type, the number of references
+/// removed, and whether the pointer is ultimately mutable or not.
+pub fn peel_mid_ty_refs_is_mutable(ty: Ty<'_>) -> (Ty<'_>, usize, Mutability) {
+    fn f(ty: Ty<'_>, count: usize, mutability: Mutability) -> (Ty<'_>, usize, Mutability) {
+        match ty.kind() {
+            ty::Ref(_, ty, Mutability::Mut) => f(ty, count + 1, mutability),
+            ty::Ref(_, ty, Mutability::Not) => f(ty, count + 1, Mutability::Not),
+            _ => (ty, count, mutability),
+        }
+    }
+    f(ty, 0, Mutability::Mut)
+}
+
+/// Returns `true` if the given type is an `unsafe` function.
+pub fn type_is_unsafe_function<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
+    match ty.kind() {
+        ty::FnDef(..) | ty::FnPtr(_) => ty.fn_sig(cx.tcx).unsafety() == Unsafety::Unsafe,
+        _ => false,
+    }
+}
+
+/// Returns the base type for HIR references and pointers.
+pub fn walk_ptrs_hir_ty<'tcx>(ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
+    match ty.kind {
+        TyKind::Ptr(ref mut_ty) | TyKind::Rptr(_, ref mut_ty) => walk_ptrs_hir_ty(&mut_ty.ty),
+        _ => ty,
+    }
+}
+
+/// Returns the base type for references and raw pointers, and count reference
+/// depth.
+pub fn walk_ptrs_ty_depth(ty: Ty<'_>) -> (Ty<'_>, usize) {
+    fn inner(ty: Ty<'_>, depth: usize) -> (Ty<'_>, usize) {
+        match ty.kind() {
+            ty::Ref(_, ty, _) => inner(ty, depth + 1),
+            _ => (ty, depth),
+        }
+    }
+    inner(ty, 0)
+}