Improve local generic parameter suggestions.

5 files changed, 39 insertions, 31 deletions

diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 193610ff57d..fc198350198 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/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) {
-                        // Suggest the modification to the user
-                        err.span_suggestion(
-                            sugg_span,
-                            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",
-                        );
+                    let name = self.opt_name(def_id).unwrap_or(sym::T);
+                    let (span, snippet) = if span.is_empty() {
+                        let snippet = format!("<{}>", name);
+                        (span, snippet)
                     } 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
diff --git a/compiler/rustc_resolve/src/ident.rs b/compiler/rustc_resolve/src/ident.rs
index be50eecf4b1..0d8f1cf3656 100644
--- a/compiler/rustc_resolve/src/ident.rs
+++ b/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(
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index b6fedd838bb..748a0781c4f 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/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,
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 9c213da8c2a..eb727debc91 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/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.
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 156f53ac486..c8978845ffb 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -280,6 +280,7 @@ symbols! {
         StructuralPartialEq,
         SubdiagnosticMessage,
         Sync,
+        T,
         Target,
         ToOwned,
         ToString,