Auto merge of #5528 - phansch:same-tys, r=flip1995

Cleanup: Use rustc's `same_type` for our `same_tys`

This delegates our `same_tys` to [ty::TyS::same_type][same_type] to
remove some duplication.

Our `same_tys` was introduced 4 years ago in #730. Before, it was
building an inference context to be able to call
`can_eq` to compare the types. The `rustc-dev-guide` has some more details
about `can_eq` in [Type Inference -> Trying equality][try_eq].

Now, using the rustc function, we are essentially comparing the `DefId`s
of the given types, which also makes more sense, IMO.

I also confirmed that the FIXME is resolved via a bit of `dbg!`, however
no UI tests seem to have been affected.

[same_type]: https://github.com/rust-lang/rust/blob/659951c4a0d7450e43f61c61c0e87d0ceae17087/src/librustc_middle/ty/util.rs#L777
[try_eq]: https://rustc-dev-guide.rust-lang.org/type-inference.html#trying-equality

---

changelog: none

7 files changed, 29 insertions, 47 deletions

diff --git a/clippy_lints/src/copies.rs b/clippy_lints/src/copies.rs
index 66722786eab..b6d50bdfa14 100644
--- a/clippy_lints/src/copies.rs
+++ b/clippy_lints/src/copies.rs
@@ -1,9 +1,9 @@
-use crate::utils::{get_parent_expr, higher, if_sequence, same_tys, snippet, span_lint_and_note, span_lint_and_then};
+use crate::utils::{get_parent_expr, higher, if_sequence, snippet, span_lint_and_note, span_lint_and_then};
 use crate::utils::{SpanlessEq, SpanlessHash};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::{Arm, Block, Expr, ExprKind, MatchSource, Pat, PatKind};
 use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::ty::Ty;
+use rustc_middle::ty::{Ty, TyS};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::symbol::Symbol;
 use std::collections::hash_map::Entry;
@@ -242,15 +242,11 @@ fn lint_same_fns_in_if_cond(cx: &LateContext<'_, '_>, conds: &[&Expr<'_>]) {
 
 /// Implementation of `MATCH_SAME_ARMS`.
 fn lint_match_arms<'tcx>(cx: &LateContext<'_, 'tcx>, expr: &Expr<'_>) {
-    fn same_bindings<'tcx>(
-        cx: &LateContext<'_, 'tcx>,
-        lhs: &FxHashMap<Symbol, Ty<'tcx>>,
-        rhs: &FxHashMap<Symbol, Ty<'tcx>>,
-    ) -> bool {
+    fn same_bindings<'tcx>(lhs: &FxHashMap<Symbol, Ty<'tcx>>, rhs: &FxHashMap<Symbol, Ty<'tcx>>) -> bool {
         lhs.len() == rhs.len()
             && lhs
                 .iter()
-                .all(|(name, l_ty)| rhs.get(name).map_or(false, |r_ty| same_tys(cx, l_ty, r_ty)))
+                .all(|(name, l_ty)| rhs.get(name).map_or(false, |r_ty| TyS::same_type(l_ty, r_ty)))
     }
 
     if let ExprKind::Match(_, ref arms, MatchSource::Normal) = expr.kind {
@@ -269,7 +265,7 @@ fn lint_match_arms<'tcx>(cx: &LateContext<'_, 'tcx>, expr: &Expr<'_>) {
             (min_index..=max_index).all(|index| arms[index].guard.is_none()) &&
                 SpanlessEq::new(cx).eq_expr(&lhs.body, &rhs.body) &&
                 // all patterns should have the same bindings
-                same_bindings(cx, &bindings(cx, &lhs.pat), &bindings(cx, &rhs.pat))
+                same_bindings(&bindings(cx, &lhs.pat), &bindings(cx, &rhs.pat))
         };
 
         let indexed_arms: Vec<(usize, &Arm<'_>)> = arms.iter().enumerate().collect();
diff --git a/clippy_lints/src/loops.rs b/clippy_lints/src/loops.rs
index dbe41823a9c..57c62d73964 100644
--- a/clippy_lints/src/loops.rs
+++ b/clippy_lints/src/loops.rs
@@ -8,7 +8,7 @@ use crate::utils::{
     multispan_sugg, snippet, snippet_opt, snippet_with_applicability, span_lint, span_lint_and_help,
     span_lint_and_sugg, span_lint_and_then, SpanlessEq,
 };
-use crate::utils::{is_type_diagnostic_item, qpath_res, same_tys, sugg};
+use crate::utils::{is_type_diagnostic_item, qpath_res, sugg};
 use if_chain::if_chain;
 use rustc_ast::ast;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
@@ -24,7 +24,7 @@ use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::hir::map::Map;
 use rustc_middle::lint::in_external_macro;
 use rustc_middle::middle::region;
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::{self, Ty, TyS};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
 use rustc_span::symbol::Symbol;
@@ -1256,7 +1256,7 @@ fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat<'_>, arg: &Expr<'_>, e
             } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
                 let receiver_ty = cx.tables.expr_ty(&args[0]);
                 let receiver_ty_adjusted = cx.tables.expr_ty_adjusted(&args[0]);
-                if same_tys(cx, receiver_ty, receiver_ty_adjusted) {
+                if TyS::same_type(receiver_ty, receiver_ty_adjusted) {
                     let mut applicability = Applicability::MachineApplicable;
                     let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
                     span_lint_and_sugg(
@@ -1277,7 +1277,7 @@ fn check_for_loop_arg(cx: &LateContext<'_, '_>, pat: &Pat<'_>, arg: &Expr<'_>, e
                             mutbl: Mutability::Not,
                         },
                     );
-                    if same_tys(cx, receiver_ty_adjusted, ref_receiver_ty) {
+                    if TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) {
                         lint_iter_method(cx, args, arg, method_name)
                     }
                 }
diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index a9c0ff24fa6..78d69690c2d 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -18,7 +18,7 @@ use rustc_lint::{LateContext, LateLintPass, Lint, LintContext};
 use rustc_middle::hir::map::Map;
 use rustc_middle::lint::in_external_macro;
 use rustc_middle::ty::subst::GenericArgKind;
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::{self, Ty, TyS};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
 use rustc_span::symbol::{sym, SymbolStr};
@@ -29,9 +29,9 @@ use crate::utils::{
     get_arg_name, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait, in_macro, is_copy,
     is_ctor_or_promotable_const_function, is_expn_of, is_type_diagnostic_item, iter_input_pats, last_path_segment,
     match_def_path, match_qpath, match_trait_method, match_type, match_var, method_calls, method_chain_args, paths,
-    remove_blocks, return_ty, same_tys, single_segment_path, snippet, snippet_with_applicability,
-    snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_note, span_lint_and_sugg,
-    span_lint_and_then, sugg, walk_ptrs_ty, walk_ptrs_ty_depth, SpanlessEq,
+    remove_blocks, return_ty, single_segment_path, snippet, snippet_with_applicability, snippet_with_macro_callsite,
+    span_lint, span_lint_and_help, span_lint_and_note, span_lint_and_sugg, span_lint_and_then, sugg, walk_ptrs_ty,
+    walk_ptrs_ty_depth, SpanlessEq,
 };
 
 declare_clippy_lint! {
@@ -1548,7 +1548,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {
 
             let contains_self_ty = |ty: Ty<'tcx>| {
                 ty.walk().any(|inner| match inner.unpack() {
-                    GenericArgKind::Type(inner_ty) => same_tys(cx, self_ty, inner_ty),
+                    GenericArgKind::Type(inner_ty) => TyS::same_type(self_ty, inner_ty),
 
                     GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
                 })
@@ -1575,7 +1575,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {
                 }
             }
 
-            if name == "new" && !same_tys(cx, ret_ty, self_ty) {
+            if name == "new" && !TyS::same_type(ret_ty, self_ty) {
                 span_lint(
                     cx,
                     NEW_RET_NO_SELF,
diff --git a/clippy_lints/src/new_without_default.rs b/clippy_lints/src/new_without_default.rs
index e556e5d59c1..dd236535c18 100644
--- a/clippy_lints/src/new_without_default.rs
+++ b/clippy_lints/src/new_without_default.rs
@@ -1,13 +1,13 @@
 use crate::utils::paths;
 use crate::utils::sugg::DiagnosticBuilderExt;
-use crate::utils::{get_trait_def_id, return_ty, same_tys, span_lint_hir_and_then};
+use crate::utils::{get_trait_def_id, return_ty, span_lint_hir_and_then};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_hir::HirIdSet;
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
-use rustc_middle::ty::Ty;
+use rustc_middle::ty::{Ty, TyS};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 
 declare_clippy_lint! {
@@ -93,7 +93,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NewWithoutDefault {
                             let self_def_id = cx.tcx.hir().local_def_id(cx.tcx.hir().get_parent_item(id));
                             let self_ty = cx.tcx.type_of(self_def_id);
                             if_chain! {
-                                if same_tys(cx, self_ty, return_ty(cx, id));
+                                if TyS::same_type(self_ty, return_ty(cx, id));
                                 if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT);
                                 then {
                                     if self.impling_types.is_none() {
diff --git a/clippy_lints/src/types.rs b/clippy_lints/src/types.rs
index 5ca30d598eb..bc5fe44b30f 100644
--- a/clippy_lints/src/types.rs
+++ b/clippy_lints/src/types.rs
@@ -17,7 +17,7 @@ use rustc_hir::{
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::hir::map::Map;
 use rustc_middle::lint::in_external_macro;
-use rustc_middle::ty::{self, InferTy, Ty, TyCtxt, TypeckTables};
+use rustc_middle::ty::{self, InferTy, Ty, TyCtxt, TyS, TypeckTables};
 use rustc_session::{declare_lint_pass, declare_tool_lint, impl_lint_pass};
 use rustc_span::hygiene::{ExpnKind, MacroKind};
 use rustc_span::source_map::Span;
@@ -31,7 +31,7 @@ use crate::utils::paths;
 use crate::utils::{
     clip, comparisons, differing_macro_contexts, higher, in_constant, indent_of, int_bits, is_type_diagnostic_item,
     last_path_segment, match_def_path, match_path, method_chain_args, multispan_sugg, numeric_literal::NumericLiteral,
-    qpath_res, same_tys, sext, snippet, snippet_block_with_applicability, snippet_opt, snippet_with_applicability,
+    qpath_res, sext, snippet, snippet_block_with_applicability, snippet_opt, snippet_with_applicability,
     snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then, unsext,
 };
 
@@ -2556,7 +2556,7 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 't
             if let ExprKind::Path(QPath::TypeRelative(ref ty, ref method)) = fun.kind;
             if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
             then {
-                if !same_tys(self.cx, self.target.ty(), self.body.expr_ty(e)) {
+                if !TyS::same_type(self.target.ty(), self.body.expr_ty(e)) {
                     return;
                 }
 
diff --git a/clippy_lints/src/useless_conversion.rs b/clippy_lints/src/useless_conversion.rs
index 7fa97b24699..141035a980a 100644
--- a/clippy_lints/src/useless_conversion.rs
+++ b/clippy_lints/src/useless_conversion.rs
@@ -1,12 +1,12 @@
 use crate::utils::{
-    is_type_diagnostic_item, match_def_path, match_trait_method, paths, same_tys, snippet, snippet_with_macro_callsite,
+    is_type_diagnostic_item, match_def_path, match_trait_method, paths, snippet, snippet_with_macro_callsite,
     span_lint_and_help, span_lint_and_sugg,
 };
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind, HirId, MatchSource};
 use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::ty;
+use rustc_middle::ty::{self, TyS};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 
 declare_clippy_lint! {
@@ -65,7 +65,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UselessConversion {
                 if match_trait_method(cx, e, &paths::INTO) && &*name.ident.as_str() == "into" {
                     let a = cx.tables.expr_ty(e);
                     let b = cx.tables.expr_ty(&args[0]);
-                    if same_tys(cx, a, b) {
+                    if TyS::same_type(a, b) {
                         let sugg = snippet_with_macro_callsite(cx, args[0].span, "<expr>").to_string();
                         span_lint_and_sugg(
                             cx,
@@ -81,7 +81,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UselessConversion {
                 if match_trait_method(cx, e, &paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
                     let a = cx.tables.expr_ty(e);
                     let b = cx.tables.expr_ty(&args[0]);
-                    if same_tys(cx, a, b) {
+                    if TyS::same_type(a, b) {
                         let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
                         span_lint_and_sugg(
                             cx,
@@ -101,7 +101,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UselessConversion {
                         if is_type_diagnostic_item(cx, a, sym!(result_type));
                         if let ty::Adt(_, substs) = a.kind;
                         if let Some(a_type) = substs.types().next();
-                        if same_tys(cx, a_type, b);
+                        if TyS::same_type(a_type, b);
 
                         then {
                             span_lint_and_help(
@@ -131,7 +131,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UselessConversion {
                             if is_type_diagnostic_item(cx, a, sym!(result_type));
                             if let ty::Adt(_, substs) = a.kind;
                             if let Some(a_type) = substs.types().next();
-                            if same_tys(cx, a_type, b);
+                            if TyS::same_type(a_type, b);
 
                             then {
                                 let hint = format!("consider removing `{}()`", snippet(cx, path.span, "TryFrom::try_from"));
@@ -148,7 +148,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UselessConversion {
 
                         if_chain! {
                             if match_def_path(cx, def_id, &paths::FROM_FROM);
-                            if same_tys(cx, a, b);
+                            if TyS::same_type(a, b);
 
                             then {
                                 let sugg = snippet(cx, args[0].span.source_callsite(), "<expr>").into_owned();
diff --git a/clippy_lints/src/utils/mod.rs b/clippy_lints/src/utils/mod.rs
index 2cdb6486fcb..9a6750c51ab 100644
--- a/clippy_lints/src/utils/mod.rs
+++ b/clippy_lints/src/utils/mod.rs
@@ -40,7 +40,7 @@ use rustc_hir::{
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_lint::{LateContext, Level, Lint, LintContext};
 use rustc_middle::hir::map::Map;
-use rustc_middle::ty::{self, layout::IntegerExt, subst::GenericArg, Binder, Ty, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{self, layout::IntegerExt, subst::GenericArg, Ty, TyCtxt, TypeFoldable};
 use rustc_span::hygiene::{ExpnKind, MacroKind};
 use rustc_span::source_map::original_sp;
 use rustc_span::symbol::{self, kw, Symbol};
@@ -879,20 +879,6 @@ pub fn return_ty<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, fn_item: hir::HirId) -> T
     cx.tcx.erase_late_bound_regions(&ret_ty)
 }
 
-/// Checks if two types are the same.
-///
-/// This discards any lifetime annotations, too.
-//
-// FIXME: this works correctly for lifetimes bounds (`for <'a> Foo<'a>` ==
-// `for <'b> Foo<'b>`, but not for type parameters).
-pub fn same_tys<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
-    let a = cx.tcx.erase_late_bound_regions(&Binder::bind(a));
-    let b = cx.tcx.erase_late_bound_regions(&Binder::bind(b));
-    cx.tcx
-        .infer_ctxt()
-        .enter(|infcx| infcx.can_eq(cx.param_env, a, b).is_ok())
-}
-
 /// Returns `true` if the given type is an `unsafe` function.
 pub fn type_is_unsafe_function<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty<'tcx>) -> bool {
     match ty.kind {