Auto merge of #72080 - matthewjasper:uniform-impl-trait, r=nikomatsakis

Clean up type alias impl trait implementation

- Removes special case for top-level impl trait
- Removes associated opaque types
- Forbid lifetime elision in let position impl trait. This is consistent with the behavior for inferred types.
- Handle lifetimes in type alias impl trait more uniformly with other parameters

cc #69323
cc #63063
Closes #57188
Closes #62988
Closes #69136
Closes #73061

clippy_lints/src/lifetimes.rs

@@ -379,7 +379,7 @@ impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
             TyKind::Path(ref path) => {
                 self.collect_anonymous_lifetimes(path, ty);
             },
-            TyKind::Def(item, _) => {
+            TyKind::OpaqueDef(item, _) => {
                 let map = self.cx.tcx.hir();
                 if let ItemKind::OpaqueTy(ref exist_ty) = map.expect_item(item.id).kind {
                     for bound in exist_ty.bounds {

clippy_lints/src/manual_async_fn.rs

@@ -99,7 +99,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ManualAsyncFn {
 
 fn future_trait_ref<'tcx>(cx: &LateContext<'_, 'tcx>, ty: &'tcx Ty<'tcx>) -> Option<&'tcx TraitRef<'tcx>> {
     if_chain! {
-        if let TyKind::Def(item_id, _) = ty.kind;
+        if let TyKind::OpaqueDef(item_id, _) = ty.kind;
         let item = cx.tcx.hir().item(item_id.id);
         if let ItemKind::OpaqueTy(opaque) = &item.kind;
         if opaque.bounds.len() == 1;

clippy_lints/src/missing_doc.rs

@@ -187,7 +187,6 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingDoc {
             hir::ImplItemKind::Const(..) => "an associated constant",
             hir::ImplItemKind::Fn(..) => "a method",
             hir::ImplItemKind::TyAlias(_) => "an associated type",
-            hir::ImplItemKind::OpaqueTy(_) => "an existential type",
         };
         self.check_missing_docs_attrs(cx, &impl_item.attrs, impl_item.span, desc);
     }

clippy_lints/src/missing_inline.rs

@@ -142,7 +142,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingInline {
 
         let desc = match impl_item.kind {
             hir::ImplItemKind::Fn(..) => "a method",
-            hir::ImplItemKind::Const(..) | hir::ImplItemKind::TyAlias(_) | hir::ImplItemKind::OpaqueTy(_) => return,
+            hir::ImplItemKind::Const(..) | hir::ImplItemKind::TyAlias(_) => return,
         };
 
         let def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);

clippy_lints/src/utils/hir_utils.rs

@@ -710,7 +710,7 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
                     segment.ident.name.hash(&mut self.s);
                 },
             },
-            TyKind::Def(_, arg_list) => {
+            TyKind::OpaqueDef(_, arg_list) => {
                 for arg in *arg_list {
                     match arg {
                         GenericArg::Lifetime(ref l) => self.hash_lifetime(l),

clippy_lints/src/utils/inspector.rs

@@ -63,7 +63,6 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DeepCodeInspector {
             },
             hir::ImplItemKind::Fn(..) => println!("method"),
             hir::ImplItemKind::TyAlias(_) => println!("associated type"),
-            hir::ImplItemKind::OpaqueTy(_) => println!("existential type"),
         }
     }
     // fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx