Point at inner item when using outer item type param

```
error[E0401]: can't use generic parameters from outer item
  --> $DIR/E0401.rs:4:39
   |
LL | fn foo<T>(x: T) {
   |        - type parameter from outer item
LL |     fn bfnr<U, V: Baz<U>, W: Fn()>(y: T) {
   |        ----                           ^ use of generic parameter from outer item
   |        |
   |        generic parameter used in this inner function
   |
help: try introducing a local generic parameter here
   |
LL |     fn bfnr<T, U, V: Baz<U>, W: Fn()>(y: T) {
   |             ++
```

Author: estebank

compiler/rustc_resolve/messages.ftl

@@ -180,6 +180,11 @@ resolve_generic_params_from_outer_item_const = a `const` is a separate item from
 
 resolve_generic_params_from_outer_item_const_param = const parameter from outer item
 
+resolve_generic_params_from_outer_item_inner_item = {$is_self ->
+        [true] `Self`
+        *[false] generic parameter
+    } used in this inner {$descr}
+
 resolve_generic_params_from_outer_item_self_ty_alias = `Self` type implicitly declared here, by this `impl`
 
 resolve_generic_params_from_outer_item_self_ty_param = can't use `Self` here

compiler/rustc_resolve/src/diagnostics.rs

@@ -557,6 +557,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 outer_res,
                 has_generic_params,
                 def_kind,
+                item,
             ) => {
                 use errs::GenericParamsFromOuterItemLabel as Label;
                 let static_or_const = match def_kind {
@@ -575,6 +576,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     sugg: None,
                     static_or_const,
                     is_self,
+                    item: item.map(|(span, descr)| errs::GenericParamsFromOuterItemInnerItem {
+                        span,
+                        descr,
+                    }),
                 };
 
                 let sm = self.tcx.sess.source_map();
@@ -2506,6 +2511,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         None,
                         &ribs[ns_to_try],
                         ignore_binding,
+                        None,
                     ) {
                         // we found a locally-imported or available item/module
                         Some(LexicalScopeBinding::Item(binding)) => Some(binding),
@@ -2556,6 +2562,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     None,
                     &ribs[ValueNS],
                     ignore_binding,
+                    None,
                 )
             } else {
                 None

compiler/rustc_resolve/src/errors.rs

@@ -24,6 +24,16 @@ pub(crate) struct GenericParamsFromOuterItem {
     #[subdiagnostic]
     pub(crate) static_or_const: Option<GenericParamsFromOuterItemStaticOrConst>,
     pub(crate) is_self: bool,
+    #[subdiagnostic]
+    pub(crate) item: Option<GenericParamsFromOuterItemInnerItem>,
+}
+
+#[derive(Subdiagnostic)]
+#[label(resolve_generic_params_from_outer_item_inner_item)]
+pub(crate) struct GenericParamsFromOuterItemInnerItem {
+    #[primary_span]
+    pub(crate) span: Span,
+    pub(crate) descr: String,
 }
 
 #[derive(Subdiagnostic)]

compiler/rustc_resolve/src/ident.rs

@@ -12,7 +12,9 @@ use tracing::{debug, instrument};
 
 use crate::errors::{ParamKindInEnumDiscriminant, ParamKindInNonTrivialAnonConst};
 use crate::imports::{Import, NameResolution};
-use crate::late::{ConstantHasGenerics, NoConstantGenericsReason, PathSource, Rib, RibKind};
+use crate::late::{
+    ConstantHasGenerics, DiagMetadata, NoConstantGenericsReason, PathSource, Rib, RibKind,
+};
 use crate::macros::{MacroRulesScope, sub_namespace_match};
 use crate::{
     AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, BindingKey, CmResolver, Determinacy,
@@ -295,6 +297,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         finalize: Option<Finalize>,
         ribs: &[Rib<'ra>],
         ignore_binding: Option<NameBinding<'ra>>,
+        diag_metadata: Option<&DiagMetadata<'_>>,
     ) -> Option<LexicalScopeBinding<'ra>> {
         assert!(ns == TypeNS || ns == ValueNS);
         let orig_ident = ident;
@@ -326,6 +329,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     finalize.map(|finalize| finalize.path_span),
                     *original_rib_ident_def,
                     ribs,
+                    diag_metadata,
                 )));
             } else if let RibKind::Block(Some(module)) = rib.kind
                 && let Ok(binding) = self.cm().resolve_ident_in_module_unadjusted(
@@ -1193,6 +1197,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         finalize: Option<Span>,
         original_rib_ident_def: Ident,
         all_ribs: &[Rib<'ra>],
+        diag_metadata: Option<&DiagMetadata<'_>>,
     ) -> Res {
         debug!("validate_res_from_ribs({:?})", res);
         let ribs = &all_ribs[rib_index + 1..];
@@ -1391,12 +1396,25 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     };
 
                     if let Some(span) = finalize {
+                        let item = if let Some(diag_metadata) = diag_metadata
+                            && let Some(current_item) = diag_metadata.current_item
+                        {
+                            let span = current_item
+                                .kind
+                                .ident()
+                                .map(|i| i.span)
+                                .unwrap_or(current_item.span);
+                            Some((span, current_item.kind.descr().to_string()))
+                        } else {
+                            None
+                        };
                         self.report_error(
                             span,
                             ResolutionError::GenericParamsFromOuterItem(
                                 res,
                                 has_generic_params,
                                 def_kind,
+                                item,
                             ),
                         );
                     }
@@ -1472,6 +1490,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                                 res,
                                 has_generic_params,
                                 def_kind,
+                                None,
                             ),
                         );
                     }
@@ -1501,6 +1520,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             None,
             None,
             ignore_import,
+            None,
         )
     }
     #[instrument(level = "debug", skip(self))]
@@ -1522,6 +1542,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             None,
             ignore_binding,
             ignore_import,
+            None,
         )
     }
 
@@ -1535,6 +1556,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         ribs: Option<&PerNS<Vec<Rib<'ra>>>>,
         ignore_binding: Option<NameBinding<'ra>>,
         ignore_import: Option<Import<'ra>>,
+        diag_metadata: Option<&DiagMetadata<'_>>,
     ) -> PathResult<'ra> {
         let mut module = None;
         let mut module_had_parse_errors = false;
@@ -1675,6 +1697,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     finalize,
                     &ribs[ns],
                     ignore_binding,
+                    diag_metadata,
                 ) {
                     // we found a locally-imported or available item/module
                     Some(LexicalScopeBinding::Item(binding)) => Ok(binding),

compiler/rustc_resolve/src/late.rs

@@ -667,7 +667,7 @@ pub(crate) struct UnnecessaryQualification<'ra> {
 }
 
 #[derive(Default, Debug)]
-struct DiagMetadata<'ast> {
+pub(crate) struct DiagMetadata<'ast> {
     /// The current trait's associated items' ident, used for diagnostic suggestions.
     current_trait_assoc_items: Option<&'ast [Box<AssocItem>]>,
 
@@ -678,7 +678,7 @@ struct DiagMetadata<'ast> {
     current_self_item: Option<NodeId>,
 
     /// The current trait (used to suggest).
-    current_item: Option<&'ast Item>,
+    pub(crate) current_item: Option<&'ast Item>,
 
     /// When processing generic arguments and encountering an unresolved ident not found,
     /// suggest introducing a type or const param depending on the context.
@@ -885,6 +885,7 @@ impl<'ast, 'ra, 'tcx> Visitor<'ast> for LateResolutionVisitor<'_, 'ast, 'ra, 'tc
                         TypeNS,
                         Some(Finalize::new(ty.id, ty.span)),
                         None,
+                        None,
                     )
                     .map_or(Res::Err, |d| d.res());
                 self.r.record_partial_res(ty.id, PartialRes::new(res));
@@ -1457,6 +1458,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             None,
             &self.ribs[ns],
             None,
+            None,
         )
     }
 
@@ -1466,6 +1468,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
         ns: Namespace,
         finalize: Option<Finalize>,
         ignore_binding: Option<NameBinding<'ra>>,
+        diag_metadata: Option<&crate::late::DiagMetadata<'_>>,
     ) -> Option<LexicalScopeBinding<'ra>> {
         self.r.resolve_ident_in_lexical_scope(
             ident,
@@ -1474,6 +1477,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             finalize,
             &self.ribs[ns],
             ignore_binding,
+            diag_metadata,
         )
     }
 
@@ -1493,6 +1497,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             Some(&self.ribs),
             None,
             None,
+            Some(&self.diag_metadata),
         )
     }
 
@@ -2551,8 +2556,8 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                         report_error(self, ns);
                     }
                     Some(LexicalScopeBinding::Item(binding)) => {
-                        if let Some(LexicalScopeBinding::Res(..)) =
-                            self.resolve_ident_in_lexical_scope(ident, ns, None, Some(binding))
+                        if let Some(LexicalScopeBinding::Res(..)) = self
+                            .resolve_ident_in_lexical_scope(ident, ns, None, Some(binding), None)
                         {
                             report_error(self, ns);
                         }
@@ -5105,7 +5110,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             // use the type namespace
             let ns = if i + 1 == path.len() { ns } else { TypeNS };
             let res = self.r.partial_res_map.get(&seg.id?)?.full_res()?;
-            let binding = self.resolve_ident_in_lexical_scope(seg.ident, ns, None, None)?;
+            let binding = self.resolve_ident_in_lexical_scope(seg.ident, ns, None, None, None)?;
             (res == binding.res()).then_some((seg, binding))
         });
 

compiler/rustc_resolve/src/lib.rs

@@ -241,7 +241,7 @@ struct BindingError {
 #[derive(Debug)]
 enum ResolutionError<'ra> {
     /// Error E0401: can't use type or const parameters from outer item.
-    GenericParamsFromOuterItem(Res, HasGenericParams, DefKind),
+    GenericParamsFromOuterItem(Res, HasGenericParams, DefKind, Option<(Span, String)>),
     /// Error E0403: the name is already used for a type or const parameter in this generic
     /// parameter list.
     NameAlreadyUsedInParameterList(Ident, Span),

tests/ui/delegation/target-expr.stderr

@@ -3,7 +3,9 @@ error[E0401]: can't use generic parameters from outer item
    |
 LL | fn bar<T: Default>(_: T) {
    |        - type parameter from outer item
-...
+LL |     reuse Trait::static_method {
+   |                  ------------- generic parameter used in this inner delegated function
+LL |
 LL |         let _ = T::Default();
    |                 ^^^^^^^^^^ use of generic parameter from outer item
    |

tests/ui/error-codes/E0401.stderr

@@ -4,7 +4,9 @@ error[E0401]: can't use generic parameters from outer item
 LL | fn foo<T>(x: T) {
    |        - type parameter from outer item
 LL |     fn bfnr<U, V: Baz<U>, W: Fn()>(y: T) {
-   |                                       ^ use of generic parameter from outer item
+   |        ----                           ^ use of generic parameter from outer item
+   |        |
+   |        generic parameter used in this inner function
    |
 help: try introducing a local generic parameter here
    |
@@ -17,6 +19,9 @@ error[E0401]: can't use generic parameters from outer item
 LL | fn foo<T>(x: T) {
    |        - type parameter from outer item
 ...
+LL |     fn baz<U,
+   |        --- generic parameter used in this inner function
+...
 LL |            (y: T) {
    |                ^ use of generic parameter from outer item
    |
@@ -32,10 +37,11 @@ LL | impl<T> Iterator for A<T> {
    | ---- `Self` type implicitly declared here, by this `impl`
 ...
 LL |         fn helper(sel: &Self) -> u8 {
-   |                         ^^^^
-   |                         |
-   |                         use of `Self` from outer item
-   |                         refer to the type directly here instead
+   |            ------       ^^^^
+   |            |            |
+   |            |            use of `Self` from outer item
+   |            |            refer to the type directly here instead
+   |            `Self` used in this inner function
 
 error: aborting due to 3 previous errors
 

tests/ui/generics/enum-definition-with-outer-generic-parameter-5997.stderr

@@ -4,7 +4,9 @@ error[E0401]: can't use generic parameters from outer item
 LL | fn f<Z>() -> bool {
    |      - type parameter from outer item
 LL |     enum E { V(Z) }
-   |                ^ use of generic parameter from outer item
+   |          -     ^ use of generic parameter from outer item
+   |          |
+   |          generic parameter used in this inner enum
    |
 help: try introducing a local generic parameter here
    |

tests/ui/generics/generic-params-nested-fn-scope-error.stderr

@@ -4,7 +4,9 @@ error[E0401]: can't use generic parameters from outer item
 LL | fn foo<U>(v: Vec<U>) -> U {
    |        - type parameter from outer item
 LL |     fn bar(w: [U]) -> U {
-   |                ^ use of generic parameter from outer item
+   |        ---     ^ use of generic parameter from outer item
+   |        |
+   |        generic parameter used in this inner function
    |
 help: try introducing a local generic parameter here
    |
@@ -17,7 +19,9 @@ error[E0401]: can't use generic parameters from outer item
 LL | fn foo<U>(v: Vec<U>) -> U {
    |        - type parameter from outer item
 LL |     fn bar(w: [U]) -> U {
-   |                       ^ use of generic parameter from outer item
+   |        ---            ^ use of generic parameter from outer item
+   |        |
+   |        generic parameter used in this inner function
    |
 help: try introducing a local generic parameter here
    |