Improve local generic parameter suggestions.

compiler/rustc_resolve/src/diagnostics.rs

@@ -511,7 +511,7 @@ impl<'a> Resolver<'a> {
                 err.span_label(span, "use of generic parameter from outer function");
 
                 let sm = self.session.source_map();
-                match outer_res {
+                let def_id = match outer_res {
                     Res::SelfTy { trait_: maybe_trait_defid, alias_to: maybe_impl_defid } => {
                         if let Some(impl_span) =
                             maybe_impl_defid.and_then(|(def_id, _)| self.opt_span(def_id))
@@ -536,11 +536,13 @@ impl<'a> Resolver<'a> {
                         if let Some(span) = self.opt_span(def_id) {
                             err.span_label(span, "type parameter from outer function");
                         }
+                        def_id
                     }
                     Res::Def(DefKind::ConstParam, def_id) => {
                         if let Some(span) = self.opt_span(def_id) {
                             err.span_label(span, "const parameter from outer function");
                         }
+                        def_id
                     }
                     _ => {
                         bug!(
@@ -548,28 +550,23 @@ impl<'a> Resolver<'a> {
                             DefKind::TyParam or DefKind::ConstParam"
                         );
                     }
-                }
+                };
 
-                if let HasGenericParams::Yes = has_generic_params {
+                if let HasGenericParams::Yes(span) = has_generic_params {
                     // Try to retrieve the span of the function signature and generate a new
                     // message with a local type or const parameter.
                     let sugg_msg = "try using a local generic parameter instead";
-                    if let Some((sugg_span, snippet)) = sm.generate_local_type_param_snippet(span) {
+                    let name = self.opt_name(def_id).unwrap_or(sym::T);
-                        // Suggest the modification to the user
+                    let (span, snippet) = if span.is_empty() {
-                        err.span_suggestion(
+                        let snippet = format!("<{}>", name);
-                            sugg_span,
+                        (span, snippet)
-                            sugg_msg,
-                            snippet,
-                            Applicability::MachineApplicable,
-                        );
-                    } else if let Some(sp) = sm.generate_fn_name_span(span) {
-                        err.span_label(
-                            sp,
-                            "try adding a local generic parameter in this method instead",
-                        );
                     } else {
-                        err.help("try using a local generic parameter instead");
+                        let span = sm.span_through_char(span, '<').shrink_to_hi();
-                    }
+                        let snippet = format!("{}, ", name);
+                        (span, snippet)
+                    };
+                    // Suggest the modification to the user
+                    err.span_suggestion(span, sugg_msg, snippet, Applicability::MachineApplicable);
                 }
 
                 err

compiler/rustc_resolve/src/ident.rs

@@ -1170,10 +1170,11 @@ impl<'a> Resolver<'a> {
                     let has_generic_params: HasGenericParams = match rib.kind {
                         NormalRibKind
                         | ClosureOrAsyncRibKind
-                        | AssocItemRibKind
                         | ModuleRibKind(..)
                         | MacroDefinition(..)
                         | InlineAsmSymRibKind
+                        | FnItemRibKind
+                        | AssocItemRibKind
                         | ForwardGenericParamBanRibKind => {
                             // Nothing to do. Continue.
                             continue;
@@ -1211,7 +1212,6 @@ impl<'a> Resolver<'a> {
 
                         // This was an attempt to use a type parameter outside its scope.
                         ItemRibKind(has_generic_params) => has_generic_params,
-                        FnItemRibKind => HasGenericParams::Yes,
                         ConstParamTyRibKind => {
                             if let Some(span) = finalize {
                                 self.report_error(
@@ -1248,10 +1248,11 @@ impl<'a> Resolver<'a> {
                     let has_generic_params = match rib.kind {
                         NormalRibKind
                         | ClosureOrAsyncRibKind
-                        | AssocItemRibKind
                         | ModuleRibKind(..)
                         | MacroDefinition(..)
                         | InlineAsmSymRibKind
+                        | FnItemRibKind
+                        | AssocItemRibKind
                         | ForwardGenericParamBanRibKind => continue,
 
                         ConstantItemRibKind(trivial, _) => {
@@ -1278,7 +1279,6 @@ impl<'a> Resolver<'a> {
                         }
 
                         ItemRibKind(has_generic_params) => has_generic_params,
-                        FnItemRibKind => HasGenericParams::Yes,
                         ConstParamTyRibKind => {
                             if let Some(span) = finalize {
                                 self.report_error(

compiler/rustc_resolve/src/late.rs

@@ -93,7 +93,7 @@ enum PatBoundCtx {
 /// Does this the item (from the item rib scope) allow generic parameters?
 #[derive(Copy, Clone, Debug)]
 pub(crate) enum HasGenericParams {
-    Yes,
+    Yes(Span),
     No,
 }
 
@@ -758,7 +758,7 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
                 self.with_lifetime_rib(LifetimeRibKind::Item, |this| {
                     this.with_generic_param_rib(
                         &generics.params,
-                        ItemRibKind(HasGenericParams::Yes),
+                        ItemRibKind(HasGenericParams::Yes(generics.span)),
                         LifetimeRibKind::Generics {
                             binder: foreign_item.id,
                             kind: LifetimeBinderKind::Item,
@@ -772,7 +772,7 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
                 self.with_lifetime_rib(LifetimeRibKind::Item, |this| {
                     this.with_generic_param_rib(
                         &generics.params,
-                        ItemRibKind(HasGenericParams::Yes),
+                        ItemRibKind(HasGenericParams::Yes(generics.span)),
                         LifetimeRibKind::Generics {
                             binder: foreign_item.id,
                             kind: LifetimeBinderKind::Function,
@@ -2078,7 +2078,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
         self.with_current_self_item(item, |this| {
             this.with_generic_param_rib(
                 &generics.params,
-                ItemRibKind(HasGenericParams::Yes),
+                ItemRibKind(HasGenericParams::Yes(generics.span)),
                 LifetimeRibKind::Generics {
                     binder: item.id,
                     kind: LifetimeBinderKind::Item,
@@ -2148,7 +2148,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             ItemKind::TyAlias(box TyAlias { ref generics, .. }) => {
                 self.with_generic_param_rib(
                     &generics.params,
-                    ItemRibKind(HasGenericParams::Yes),
+                    ItemRibKind(HasGenericParams::Yes(generics.span)),
                     LifetimeRibKind::Generics {
                         binder: item.id,
                         kind: LifetimeBinderKind::Item,
@@ -2161,7 +2161,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             ItemKind::Fn(box Fn { ref generics, .. }) => {
                 self.with_generic_param_rib(
                     &generics.params,
-                    ItemRibKind(HasGenericParams::Yes),
+                    ItemRibKind(HasGenericParams::Yes(generics.span)),
                     LifetimeRibKind::Generics {
                         binder: item.id,
                         kind: LifetimeBinderKind::Function,
@@ -2193,7 +2193,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 // Create a new rib for the trait-wide type parameters.
                 self.with_generic_param_rib(
                     &generics.params,
-                    ItemRibKind(HasGenericParams::Yes),
+                    ItemRibKind(HasGenericParams::Yes(generics.span)),
                     LifetimeRibKind::Generics {
                         binder: item.id,
                         kind: LifetimeBinderKind::Item,
@@ -2217,7 +2217,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 // Create a new rib for the trait-wide type parameters.
                 self.with_generic_param_rib(
                     &generics.params,
-                    ItemRibKind(HasGenericParams::Yes),
+                    ItemRibKind(HasGenericParams::Yes(generics.span)),
                     LifetimeRibKind::Generics {
                         binder: item.id,
                         kind: LifetimeBinderKind::Item,
@@ -2605,7 +2605,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
         // If applicable, create a rib for the type parameters.
         self.with_generic_param_rib(
             &generics.params,
-            ItemRibKind(HasGenericParams::Yes),
+            ItemRibKind(HasGenericParams::Yes(generics.span)),
             LifetimeRibKind::Generics {
                 span: generics.span,
                 binder: item_id,

compiler/rustc_resolve/src/lib.rs

@@ -1945,6 +1945,16 @@ impl<'a> Resolver<'a> {
         def_id.as_local().map(|def_id| self.source_span[def_id])
     }
 
+    /// Retrieves the name of the given `DefId`.
+    #[inline]
+    pub fn opt_name(&self, def_id: DefId) -> Option<Symbol> {
+        let def_key = match def_id.as_local() {
+            Some(def_id) => self.definitions.def_key(def_id),
+            None => self.cstore().def_key(def_id),
+        };
+        def_key.get_opt_name()
+    }
+
     /// Checks if an expression refers to a function marked with
     /// `#[rustc_legacy_const_generics]` and returns the argument index list
     /// from the attribute.

compiler/rustc_span/src/symbol.rs

@@ -280,6 +280,7 @@ symbols! {
         StructuralPartialEq,
         SubdiagnosticMessage,
         Sync,
+        T,
         Target,
         ToOwned,
         ToString,

src/test/ui/const-generics/early/const-param-from-outer-fn.stderr

@@ -4,7 +4,7 @@ error[E0401]: can't use generic parameters from outer function
 LL | fn foo<const X: u32>() {
    |              - const parameter from outer function
 LL |     fn bar() -> u32 {
-   |        --- try adding a local generic parameter in this method instead
+   |           - help: try using a local generic parameter instead: `<X>`
 LL |         X
    |         ^ use of generic parameter from outer function
 

src/test/ui/error-codes/E0401.stderr

@@ -4,9 +4,9 @@ error[E0401]: can't use generic parameters from outer function
 LL | fn foo<T>(x: T) {
    |        - type parameter from outer function
 LL |     fn bfnr<U, V: Baz<U>, W: Fn()>(y: T) {
-   |        ---------------------------    ^ use of generic parameter from outer function
+   |             -                         ^ use of generic parameter from outer function
    |             |
-   |        help: try using a local generic parameter instead: `bfnr<U, V: Baz<U>, W: Fn(), T>`
+   |             help: try using a local generic parameter instead: `T,`
 
 error[E0401]: can't use generic parameters from outer function
   --> $DIR/E0401.rs:9:16
@@ -15,7 +15,7 @@ LL | fn foo<T>(x: T) {
    |        - type parameter from outer function
 ...
 LL |     fn baz<U,
-   |        --- try adding a local generic parameter in this method instead
+   |            - help: try using a local generic parameter instead: `T,`
 ...
 LL |            (y: T) {
    |                ^ use of generic parameter from outer function

src/test/ui/generics/issue-98432.stderr

@@ -5,9 +5,9 @@ LL | impl<T> Struct<T> {
    |      - type parameter from outer function
 LL |     const CONST: fn() = || {
 LL |         struct _Obligation where T:;
-   |                                  ^ use of generic parameter from outer function
+   |                           -      ^ use of generic parameter from outer function
-   |
+   |                           |
-   = help: try using a local generic parameter instead
+   |                           help: try using a local generic parameter instead: `<T>`
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-3214.stderr

@@ -2,10 +2,9 @@ error[E0401]: can't use generic parameters from outer function
   --> $DIR/issue-3214.rs:3:12
    |
 LL | fn foo<T>() {
-   |    --- - type parameter from outer function
+   |        - type parameter from outer function
-   |    |
-   |    try adding a local generic parameter in this method instead
 LL |     struct Foo {
+   |               - help: try using a local generic parameter instead: `<T>`
 LL |         x: T,
    |            ^ use of generic parameter from outer function
 

src/test/ui/issues/issue-5997-enum.stderr

@@ -2,11 +2,11 @@ error[E0401]: can't use generic parameters from outer function
   --> $DIR/issue-5997-enum.rs:2:16
    |
 LL | fn f<Z>() -> bool {
-   |    - - type parameter from outer function
+   |      - type parameter from outer function
-   |    |
-   |    try adding a local generic parameter in this method instead
 LL |     enum E { V(Z) }
-   |                ^ use of generic parameter from outer function
+   |           -    ^ use of generic parameter from outer function
+   |           |
+   |           help: try using a local generic parameter instead: `<Z>`
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-5997-struct.stderr

@@ -2,11 +2,11 @@ error[E0401]: can't use generic parameters from outer function
   --> $DIR/issue-5997-struct.rs:2:14
    |
 LL | fn f<T>() -> bool {
-   |    - - type parameter from outer function
+   |      - type parameter from outer function
-   |    |
-   |    try adding a local generic parameter in this method instead
 LL |     struct S(T);
-   |              ^ use of generic parameter from outer function
+   |             -^ use of generic parameter from outer function
+   |             |
+   |             help: try using a local generic parameter instead: `<T>`
 
 error: aborting due to previous error
 

src/test/ui/nested-ty-params.stderr

@@ -4,9 +4,9 @@ error[E0401]: can't use generic parameters from outer function
 LL | fn hd<U>(v: Vec<U> ) -> U {
    |       - type parameter from outer function
 LL |     fn hd1(w: [U]) -> U { return w[0]; }
-   |        ---     ^ use of generic parameter from outer function
+   |           -    ^ use of generic parameter from outer function
    |           |
-   |        help: try using a local generic parameter instead: `hd1<U>`
+   |           help: try using a local generic parameter instead: `<U>`
 
 error[E0401]: can't use generic parameters from outer function
   --> $DIR/nested-ty-params.rs:3:23
@@ -14,9 +14,9 @@ error[E0401]: can't use generic parameters from outer function
 LL | fn hd<U>(v: Vec<U> ) -> U {
    |       - type parameter from outer function
 LL |     fn hd1(w: [U]) -> U { return w[0]; }
-   |        ---            ^ use of generic parameter from outer function
+   |           -           ^ use of generic parameter from outer function
    |           |
-   |        help: try using a local generic parameter instead: `hd1<U>`
+   |           help: try using a local generic parameter instead: `<U>`
 
 error: aborting due to 2 previous errors
 

src/test/ui/resolve/bad-type-env-capture.stderr

@@ -4,9 +4,9 @@ error[E0401]: can't use generic parameters from outer function
 LL | fn foo<T>() {
    |        - type parameter from outer function
 LL |     fn bar(b: T) { }
-   |        ---    ^ use of generic parameter from outer function
+   |           -   ^ use of generic parameter from outer function
    |           |
-   |        help: try using a local generic parameter instead: `bar<T>`
+   |           help: try using a local generic parameter instead: `<T>`
 
 error: aborting due to previous error
 

src/test/ui/resolve/issue-3021-c.stderr

@@ -3,22 +3,22 @@ error[E0401]: can't use generic parameters from outer function
    |
 LL | fn siphash<T>() {
    |            - type parameter from outer function
-...
+LL |
+LL |     trait U {
+   |            - help: try using a local generic parameter instead: `<T>`
 LL |         fn g(&self, x: T) -> T;
-   |            -           ^ use of generic parameter from outer function
+   |                        ^ use of generic parameter from outer function
-   |            |
-   |            help: try using a local generic parameter instead: `g<T>`
 
 error[E0401]: can't use generic parameters from outer function
   --> $DIR/issue-3021-c.rs:4:30
    |
 LL | fn siphash<T>() {
    |            - type parameter from outer function
-...
+LL |
+LL |     trait U {
+   |            - help: try using a local generic parameter instead: `<T>`
 LL |         fn g(&self, x: T) -> T;
-   |            -                 ^ use of generic parameter from outer function
+   |                              ^ use of generic parameter from outer function
-   |            |
-   |            help: try using a local generic parameter instead: `g<T>`
 
 error: aborting due to 2 previous errors
 

src/test/ui/resolve/resolve-type-param-in-item-in-trait.stderr

@@ -4,8 +4,8 @@ error[E0401]: can't use generic parameters from outer function
 LL | trait TraitA<A> {
    |              - type parameter from outer function
 LL |     fn outer(&self) {
-   |        ----- try adding a local generic parameter in this method instead
 LL |         enum Foo<B> {
+   |                  - help: try using a local generic parameter instead: `A,`
 LL |             Variance(A)
    |                      ^ use of generic parameter from outer function
 
@@ -15,9 +15,10 @@ error[E0401]: can't use generic parameters from outer function
 LL | trait TraitB<A> {
    |              - type parameter from outer function
 LL |     fn outer(&self) {
-   |        ----- try adding a local generic parameter in this method instead
 LL |         struct Foo<B>(A);
-   |                       ^ use of generic parameter from outer function
+   |                    -  ^ use of generic parameter from outer function
+   |                    |
+   |                    help: try using a local generic parameter instead: `A,`
 
 error[E0401]: can't use generic parameters from outer function
   --> $DIR/resolve-type-param-in-item-in-trait.rs:23:28
@@ -25,9 +26,10 @@ error[E0401]: can't use generic parameters from outer function
 LL | trait TraitC<A> {
    |              - type parameter from outer function
 LL |     fn outer(&self) {
-   |        ----- try adding a local generic parameter in this method instead
 LL |         struct Foo<B> { a: A }
-   |                            ^ use of generic parameter from outer function
+   |                    -       ^ use of generic parameter from outer function
+   |                    |
+   |                    help: try using a local generic parameter instead: `A,`
 
 error[E0401]: can't use generic parameters from outer function
   --> $DIR/resolve-type-param-in-item-in-trait.rs:30:22
@@ -36,9 +38,9 @@ LL | trait TraitD<A> {
    |              - type parameter from outer function
 LL |     fn outer(&self) {
 LL |         fn foo<B>(a: A) { }
-   |            ------    ^ use of generic parameter from outer function
+   |                -     ^ use of generic parameter from outer function
    |                |
-   |            help: try using a local generic parameter instead: `foo<B, A>`
+   |                help: try using a local generic parameter instead: `A,`
 
 error: aborting due to 4 previous errors
 

src/test/ui/type/type-arg-out-of-scope.stderr

@@ -4,9 +4,9 @@ error[E0401]: can't use generic parameters from outer function
 LL | fn foo<T>(x: T) {
    |        - type parameter from outer function
 LL |     fn bar(f: Box<dyn FnMut(T) -> T>) { }
-   |        ---                  ^ use of generic parameter from outer function
+   |           -                 ^ use of generic parameter from outer function
    |           |
-   |        help: try using a local generic parameter instead: `bar<T>`
+   |           help: try using a local generic parameter instead: `<T>`
 
 error[E0401]: can't use generic parameters from outer function
   --> $DIR/type-arg-out-of-scope.rs:3:35
@@ -14,9 +14,9 @@ error[E0401]: can't use generic parameters from outer function
 LL | fn foo<T>(x: T) {
    |        - type parameter from outer function
 LL |     fn bar(f: Box<dyn FnMut(T) -> T>) { }
-   |        ---                        ^ use of generic parameter from outer function
+   |           -                       ^ use of generic parameter from outer function
    |           |
-   |        help: try using a local generic parameter instead: `bar<T>`
+   |           help: try using a local generic parameter instead: `<T>`
 
 error: aborting due to 2 previous errors