Do not lower generic lifetime params when AST resolution emitted an error.

Author: cjgillot

compiler/rustc_ast_lowering/src/lib.rs

@@ -1917,14 +1917,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_generic_param(&mut self, param: &GenericParam) -> hir::GenericParam<'hir> {
         let (name, kind) = match param.kind {
             GenericParamKind::Lifetime => {
-                let param_name = if param.ident.name == kw::StaticLifetime
-                    || param.ident.name == kw::UnderscoreLifetime
-                {
-                    ParamName::Error
-                } else {
-                    let ident = self.lower_ident(param.ident);
-                    ParamName::Plain(ident)
-                };
+                // AST resolution emitted an error on those parameters, so we lower them using
+                // `ParamName::Error`.
+                let param_name =
+                    if let Some(LifetimeRes::Error) = self.resolver.get_lifetime_res(param.id) {
+                        ParamName::Error
+                    } else {
+                        let ident = self.lower_ident(param.ident);
+                        ParamName::Plain(ident)
+                    };
                 let kind =
                     hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
 
@@ -1949,10 +1950,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 )
             }
         };
-        let name = match name {
-            hir::ParamName::Plain(ident) => hir::ParamName::Plain(self.lower_ident(ident)),
-            name => name,
-        };
 
         let hir_id = self.lower_node_id(param.id);
         self.lower_attrs(hir_id, &param.attrs);

compiler/rustc_resolve/src/late.rs

@@ -1939,6 +1939,9 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                             param.ident,
                             orig_is_param,
                         );
+                        // Record lifetime res, so lowering knows there is something fishy.
+                        self.record_lifetime_res(param.id, LifetimeRes::Error);
+                        continue;
                     }
                     Entry::Vacant(entry) => {
                         entry.insert(true);
@@ -1966,6 +1969,8 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 )
                 .span_label(param.ident.span, "`'_` is a reserved lifetime name")
                 .emit();
+                // Record lifetime res, so lowering knows there is something fishy.
+                self.record_lifetime_res(param.id, LifetimeRes::Error);
                 continue;
             }
 
@@ -1979,6 +1984,8 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 )
                 .span_label(param.ident.span, "'static is a reserved lifetime name")
                 .emit();
+                // Record lifetime res, so lowering knows there is something fishy.
+                self.record_lifetime_res(param.id, LifetimeRes::Error);
                 continue;
             }
 

src/test/ui/regions/regions-name-duplicated.rs

@@ -1,6 +1,5 @@
 struct Foo<'a, 'a> {
     //~^ ERROR lifetime name `'a` declared twice
-    //~| ERROR parameter `'a` is never used [E0392]
     x: &'a isize,
 }
 

src/test/ui/regions/regions-name-duplicated.stderr

@@ -6,15 +6,6 @@ LL | struct Foo<'a, 'a> {
    |            |
    |            first declared here
 
-error[E0392]: parameter `'a` is never used
-  --> $DIR/regions-name-duplicated.rs:1:12
-   |
-LL | struct Foo<'a, 'a> {
-   |            ^^ unused parameter
-   |
-   = help: consider removing `'a`, referring to it in a field, or using a marker such as `PhantomData`
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0263, E0392.
-For more information about an error, try `rustc --explain E0263`.
+For more information about this error, try `rustc --explain E0263`.