Rollup merge of rust-lang#139568 - nnethercote:empty-trait-name, r=compiler-errors

Don't use empty trait names

Helps with rust-lang#137978. Details in individual commits.

r? ```@davidtwco```

Author: matthiaskrgr

compiler/rustc_parse/src/parser/item.rs

@@ -602,21 +602,13 @@ impl<'a> Parser<'a> {
         let polarity = self.parse_polarity();
 
         // Parse both types and traits as a type, then reinterpret if necessary.
-        let err_path = |span| ast::Path::from_ident(Ident::new(kw::Empty, span));
         let ty_first = if self.token.is_keyword(kw::For) && self.look_ahead(1, |t| t != &token::Lt)
         {
             let span = self.prev_token.span.between(self.token.span);
-            self.dcx().emit_err(errors::MissingTraitInTraitImpl {
+            return Err(self.dcx().create_err(errors::MissingTraitInTraitImpl {
                 span,
                 for_span: span.to(self.token.span),
-            });
-
-            P(Ty {
-                kind: TyKind::Path(None, err_path(span)),
-                span,
-                id: DUMMY_NODE_ID,
-                tokens: None,
-            })
+            }));
         } else {
             self.parse_ty_with_generics_recovery(&generics)?
         };
@@ -657,6 +649,7 @@ impl<'a> Parser<'a> {
                     other => {
                         if let TyKind::ImplTrait(_, bounds) = other
                             && let [bound] = bounds.as_slice()
+                            && let GenericBound::Trait(poly_trait_ref) = bound
                         {
                             // Suggest removing extra `impl` keyword:
                             // `impl<T: Default> impl Default for Wrapper<T>`
@@ -666,12 +659,12 @@ impl<'a> Parser<'a> {
                                 extra_impl_kw,
                                 impl_trait_span: ty_first.span,
                             });
+                            poly_trait_ref.trait_ref.path.clone()
                         } else {
-                            self.dcx().emit_err(errors::ExpectedTraitInTraitImplFoundType {
-                                span: ty_first.span,
-                            });
+                            return Err(self.dcx().create_err(
+                                errors::ExpectedTraitInTraitImplFoundType { span: ty_first.span },
+                            ));
                         }
-                        err_path(ty_first.span)
                     }
                 };
                 let trait_ref = TraitRef { path, ref_id: ty_first.id };

compiler/rustc_resolve/src/ident.rs

@@ -296,9 +296,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     ) -> Option<LexicalScopeBinding<'ra>> {
         assert!(ns == TypeNS || ns == ValueNS);
         let orig_ident = ident;
-        if ident.name == kw::Empty {
-            return Some(LexicalScopeBinding::Res(Res::Err));
-        }
         let (general_span, normalized_span) = if ident.name == kw::SelfUpper {
             // FIXME(jseyfried) improve `Self` hygiene
             let empty_span = ident.span.with_ctxt(SyntaxContext::root());

tests/ui/parser/impl-parsing-2.rs

@@ -0,0 +1,4 @@
+impl ! {} // OK
+
+default unsafe FAIL //~ ERROR expected item, found keyword `unsafe`
+//~^ ERROR `default` is not followed by an item

tests/ui/parser/impl-parsing-2.stderr

@@ -0,0 +1,18 @@
+error: `default` is not followed by an item
+  --> $DIR/impl-parsing-2.rs:3:1
+   |
+LL | default unsafe FAIL
+   | ^^^^^^^ the `default` qualifier
+   |
+   = note: only `fn`, `const`, `type`, or `impl` items may be prefixed by `default`
+
+error: expected item, found keyword `unsafe`
+  --> $DIR/impl-parsing-2.rs:3:9
+   |
+LL | default unsafe FAIL
+   |         ^^^^^^ expected item
+   |
+   = note: for a full list of items that can appear in modules, see <https://doc.rust-lang.org/reference/items.html>
+
+error: aborting due to 2 previous errors
+

tests/ui/parser/impl-parsing.rs

@@ -2,9 +2,4 @@ impl ! {} // OK
 impl ! where u8: Copy {} // OK
 
 impl Trait Type {} //~ ERROR missing `for` in a trait impl
-impl Trait .. {} //~ ERROR missing `for` in a trait impl
 impl ?Sized for Type {} //~ ERROR expected a trait, found type
-impl ?Sized for .. {} //~ ERROR expected a trait, found type
-
-default unsafe FAIL //~ ERROR expected item, found keyword `unsafe`
-//~^ ERROR `default` is not followed by an item

tests/ui/parser/impl-parsing.stderr

@@ -9,44 +9,11 @@ help: add `for` here
 LL | impl Trait for Type {}
    |            +++
 
-error: missing `for` in a trait impl
-  --> $DIR/impl-parsing.rs:5:11
-   |
-LL | impl Trait .. {}
-   |           ^
-   |
-help: add `for` here
-   |
-LL | impl Trait for .. {}
-   |            +++
-
 error: expected a trait, found type
-  --> $DIR/impl-parsing.rs:6:6
+  --> $DIR/impl-parsing.rs:5:6
    |
 LL | impl ?Sized for Type {}
    |      ^^^^^^
 
-error: expected a trait, found type
-  --> $DIR/impl-parsing.rs:7:6
-   |
-LL | impl ?Sized for .. {}
-   |      ^^^^^^
-
-error: `default` is not followed by an item
-  --> $DIR/impl-parsing.rs:9:1
-   |
-LL | default unsafe FAIL
-   | ^^^^^^^ the `default` qualifier
-   |
-   = note: only `fn`, `const`, `type`, or `impl` items may be prefixed by `default`
-
-error: expected item, found keyword `unsafe`
-  --> $DIR/impl-parsing.rs:9:9
-   |
-LL | default unsafe FAIL
-   |         ^^^^^^ expected item
-   |
-   = note: for a full list of items that can appear in modules, see <https://doc.rust-lang.org/reference/items.html>
-
-error: aborting due to 6 previous errors
+error: aborting due to 2 previous errors