Tweak E0401

compiler/rustc_resolve/messages.ftl

@@ -175,6 +175,7 @@ resolve_generic_params_from_outer_item =
     } from outer item
     .refer_to_type_directly = refer to the type directly here instead
     .suggestion = try introducing a local generic parameter here
+    .note = nested items are independent from their parent item for everything except for privacy and name resolution
 
 resolve_generic_params_from_outer_item_const = a `const` is a separate item from the item that contains it
 

compiler/rustc_resolve/src/diagnostics.rs

@@ -558,6 +558,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 has_generic_params,
                 def_kind,
                 inner_item,
+                current_self_ty,
             } => {
                 use errs::GenericParamsFromOuterItemLabel as Label;
                 let static_or_const = match def_kind {
@@ -595,7 +596,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             sm,
                             self.def_span(def_id),
                         )));
-                        err.refer_to_type_directly = Some(span);
+                        err.refer_to_type_directly =
+                            current_self_ty.map(|snippet| errs::UseTypeDirectly { span, snippet });
                         return self.dcx().create_err(err);
                     }
                     Res::Def(DefKind::TyParam, def_id) => {

compiler/rustc_resolve/src/errors.rs

@@ -11,14 +11,15 @@ use crate::{Res, fluent_generated as fluent};
 
 #[derive(Diagnostic)]
 #[diag(resolve_generic_params_from_outer_item, code = E0401)]
+#[note]
 pub(crate) struct GenericParamsFromOuterItem {
     #[primary_span]
     #[label]
     pub(crate) span: Span,
     #[subdiagnostic]
     pub(crate) label: Option<GenericParamsFromOuterItemLabel>,
-    #[label(resolve_refer_to_type_directly)]
-    pub(crate) refer_to_type_directly: Option<Span>,
+    #[subdiagnostic]
+    pub(crate) refer_to_type_directly: Option<UseTypeDirectly>,
     #[subdiagnostic]
     pub(crate) sugg: Option<GenericParamsFromOuterItemSugg>,
     #[subdiagnostic]
@@ -68,6 +69,18 @@ pub(crate) struct GenericParamsFromOuterItemSugg {
     pub(crate) span: Span,
     pub(crate) snippet: String,
 }
+#[derive(Subdiagnostic)]
+#[suggestion(
+    resolve_refer_to_type_directly,
+    code = "{snippet}",
+    applicability = "maybe-incorrect",
+    style = "verbose"
+)]
+pub(crate) struct UseTypeDirectly {
+    #[primary_span]
+    pub(crate) span: Span,
+    pub(crate) snippet: String,
+}
 
 #[derive(Diagnostic)]
 #[diag(resolve_name_is_already_used_as_generic_parameter, code = E0403)]

compiler/rustc_resolve/src/ident.rs

@@ -326,7 +326,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     i,
                     rib_ident,
                     *res,
-                    finalize.map(|finalize| finalize.path_span),
+                    finalize.map(|_| general_span),
                     *original_rib_ident_def,
                     ribs,
                     diag_metadata,
@@ -1415,6 +1415,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                                 has_generic_params,
                                 def_kind,
                                 inner_item: item,
+                                current_self_ty: diag_metadata
+                                    .and_then(|m| m.current_self_type.as_ref())
+                                    .and_then(|ty| {
+                                        self.tcx.sess.source_map().span_to_snippet(ty.span).ok()
+                                    }),
                             },
                         );
                     }
@@ -1503,6 +1508,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                                 has_generic_params,
                                 def_kind,
                                 inner_item: item,
+                                current_self_ty: diag_metadata
+                                    .and_then(|m| m.current_self_type.as_ref())
+                                    .and_then(|ty| {
+                                        self.tcx.sess.source_map().span_to_snippet(ty.span).ok()
+                                    }),
                             },
                         );
                     }

compiler/rustc_resolve/src/late.rs

@@ -675,7 +675,7 @@ pub(crate) struct DiagMetadata<'ast> {
     current_trait_assoc_items: Option<&'ast [Box<AssocItem>]>,
 
     /// The current self type if inside an impl (used for better errors).
-    current_self_type: Option<Ty>,
+    pub(crate) current_self_type: Option<Ty>,
 
     /// The current self item if inside an ADT (used for better errors).
     current_self_item: Option<NodeId>,

compiler/rustc_resolve/src/lib.rs

@@ -246,6 +246,7 @@ enum ResolutionError<'ra> {
         has_generic_params: HasGenericParams,
         def_kind: DefKind,
         inner_item: Option<(Span, ast::ItemKind)>,
+        current_self_ty: Option<String>,
     },
     /// Error E0403: the name is already used for a type or const parameter in this generic
     /// parameter list.

tests/ui/associated-item/associated-item-duplicate-bounds.stderr

@@ -2,7 +2,7 @@ error: generic parameters may not be used in const operations
   --> $DIR/associated-item-duplicate-bounds.rs:7:18
    |
 LL |     links: [u32; A::LINKS], // Shouldn't suggest bounds already there.
-   |                  ^^^^^^^^ cannot perform const operation using `A`
+   |                  ^ cannot perform const operation using `A`
    |
    = note: type parameters may not be used in const expressions
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions

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

@@ -8,6 +8,7 @@ LL |     fn bar() -> u32 {
 LL |         X
    |         ^ use of generic parameter from outer item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 help: try introducing a local generic parameter here
    |
 LL |     fn bar<X>() -> u32 {

tests/ui/delegation/target-expr.stderr

@@ -7,7 +7,9 @@ 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
+   |                 ^ use of generic parameter from outer item
+   |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 
 error[E0434]: can't capture dynamic environment in a fn item
   --> $DIR/target-expr.rs:26:17

tests/ui/error-codes/E0401.stderr

@@ -8,6 +8,7 @@ LL |     fn bfnr<U, V: Baz<U>, W: Fn()>(y: T) {
    |        |
    |        generic parameter used in this inner function
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 help: try introducing a local generic parameter here
    |
 LL |     fn bfnr<T, U, V: Baz<U>, W: Fn()>(y: T) {
@@ -25,6 +26,7 @@ LL |     fn baz<U,
 LL |            (y: T) {
    |                ^ use of generic parameter from outer item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 help: try introducing a local generic parameter here
    |
 LL |     fn baz<T, U,
@@ -37,11 +39,16 @@ 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
+   |            |
    |            `Self` used in this inner function
+   |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
+help: refer to the type directly here instead
+   |
+LL -         fn helper(sel: &Self) -> u8 {
+LL +         fn helper(sel: &A<T>) -> u8 {
+   |
 
 error: aborting due to 3 previous errors
 

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

@@ -8,6 +8,7 @@ LL |     enum E { V(Z) }
    |          |
    |          generic parameter used in this inner enum
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 help: try introducing a local generic parameter here
    |
 LL |     enum E<Z> { V(Z) }

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

@@ -8,6 +8,7 @@ LL |     fn bar(w: [U]) -> U {
    |        |
    |        generic parameter used in this inner function
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 help: try introducing a local generic parameter here
    |
 LL |     fn bar<U>(w: [U]) -> U {
@@ -23,6 +24,7 @@ LL |     fn bar(w: [U]) -> U {
    |        |
    |        generic parameter used in this inner function
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 help: try introducing a local generic parameter here
    |
 LL |     fn bar<U>(w: [U]) -> U {

tests/ui/generics/invalid-type-param-default.stderr

@@ -2,7 +2,7 @@ error[E0128]: generic parameter defaults cannot reference parameters before they
   --> $DIR/invalid-type-param-default.rs:12:12
    |
 LL | fn mdn<T = T::Item>(_: T) {}
-   |            ^^^^^^^ cannot reference `T` before it is declared
+   |            ^ cannot reference `T` before it is declared
 
 error: defaults for generic parameters are not allowed here
   --> $DIR/invalid-type-param-default.rs:7:8

tests/ui/generics/issue-98432.stderr

@@ -9,6 +9,7 @@ LL |         struct _Obligation where T:;
    |                |
    |                generic parameter used in this inner struct
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 help: try introducing a local generic parameter here
    |
 LL |         struct _Obligation<T> where T:;

tests/ui/resolve/bad-type-env-capture.stderr

@@ -8,6 +8,7 @@ LL |     fn bar(b: T) { }
    |        |
    |        generic parameter used in this inner function
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 help: try introducing a local generic parameter here
    |
 LL |     fn bar<T>(b: T) { }

tests/ui/resolve/generic-params-from-outer-item-in-const-item.default.stderr

@@ -4,10 +4,11 @@ error[E0401]: can't use generic parameters from outer item
 LL | fn outer<T: Tr>() { // outer function
    |          - type parameter from outer item
 LL |     const K: u32 = T::C;
-   |           -        ^^^^ use of generic parameter from outer item
+   |           -        ^ use of generic parameter from outer item
    |           |
    |           generic parameter used in this inner constant item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `const` is a separate item from the item that contains it
 
 error[E0401]: can't use generic parameters from outer item
@@ -17,10 +18,11 @@ LL | impl<T> Tr for T { // outer impl block
    |      - type parameter from outer item
 LL |     const C: u32 = {
 LL |         const I: u32 = T::C;
-   |               -        ^^^^ use of generic parameter from outer item
+   |               -        ^ use of generic parameter from outer item
    |               |
    |               generic parameter used in this inner constant item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `const` is a separate item from the item that contains it
 
 error[E0401]: can't use generic parameters from outer item
@@ -29,10 +31,11 @@ error[E0401]: can't use generic parameters from outer item
 LL | struct S<T: Tr>(U32<{ // outer struct
    |          - type parameter from outer item
 LL |     const _: u32 = T::C;
-   |           -        ^^^^ use of generic parameter from outer item
+   |           -        ^ use of generic parameter from outer item
    |           |
    |           generic parameter used in this inner constant item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `const` is a separate item from the item that contains it
 
 error: aborting due to 3 previous errors

tests/ui/resolve/generic-params-from-outer-item-in-const-item.generic_const_items.stderr

@@ -4,10 +4,11 @@ error[E0401]: can't use generic parameters from outer item
 LL | fn outer<T: Tr>() { // outer function
    |          - type parameter from outer item
 LL |     const K: u32 = T::C;
-   |           -        ^^^^ use of generic parameter from outer item
+   |           -        ^ use of generic parameter from outer item
    |           |
    |           generic parameter used in this inner constant item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `const` is a separate item from the item that contains it
 help: try introducing a local generic parameter here
    |
@@ -21,10 +22,11 @@ LL | impl<T> Tr for T { // outer impl block
    |      - type parameter from outer item
 LL |     const C: u32 = {
 LL |         const I: u32 = T::C;
-   |               -        ^^^^ use of generic parameter from outer item
+   |               -        ^ use of generic parameter from outer item
    |               |
    |               generic parameter used in this inner constant item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `const` is a separate item from the item that contains it
 help: try introducing a local generic parameter here
    |
@@ -37,10 +39,11 @@ error[E0401]: can't use generic parameters from outer item
 LL | struct S<T: Tr>(U32<{ // outer struct
    |          - type parameter from outer item
 LL |     const _: u32 = T::C;
-   |           -        ^^^^ use of generic parameter from outer item
+   |           -        ^ use of generic parameter from outer item
    |           |
    |           generic parameter used in this inner constant item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `const` is a separate item from the item that contains it
 help: try introducing a local generic parameter here
    |

tests/ui/resolve/issue-12796.stderr

@@ -7,6 +7,8 @@ LL |         fn inner(_: &Self) {
    |            |         use of `Self` from outer item
    |            |         can't use `Self` here
    |            `Self` used in this inner function
+   |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 
 error: aborting due to 1 previous error
 

tests/ui/resolve/issue-3021-c.stderr

@@ -9,6 +9,7 @@ LL |     trait U {
 LL |         fn g(&self, x: T) -> T;
    |                        ^ use of generic parameter from outer item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 help: try introducing a local generic parameter here
    |
 LL |     trait U<T> {
@@ -25,6 +26,7 @@ LL |     trait U {
 LL |         fn g(&self, x: T) -> T;
    |                              ^ use of generic parameter from outer item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 help: try introducing a local generic parameter here
    |
 LL |     trait U<T> {

tests/ui/resolve/issue-3214.stderr

@@ -8,6 +8,7 @@ LL |     struct Foo {
 LL |         x: T,
    |            ^ use of generic parameter from outer item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
 help: try introducing a local generic parameter here
    |
 LL |     struct Foo<T> {

tests/ui/resolve/issue-39559.stderr

@@ -2,7 +2,7 @@ error: generic parameters may not be used in const operations
   --> $DIR/issue-39559.rs:14:18
    |
 LL |     entries: [T; D::dim()],
-   |                  ^^^^^^ cannot perform const operation using `D`
+   |                  ^ cannot perform const operation using `D`
    |
    = note: type parameters may not be used in const expressions
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions

tests/ui/resolve/issue-65025-extern-static-parent-generics.stderr

@@ -10,6 +10,7 @@ LL | |
 LL | |     }
    | |_____- generic parameter used in this inner extern block
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `static` is a separate item from the item that contains it
 
 error: aborting due to 1 previous error

tests/ui/resolve/issue-65035-static-with-parent-generics.stderr

@@ -10,6 +10,7 @@ LL | |
 LL | |     }
    | |_____- generic parameter used in this inner extern block
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `static` is a separate item from the item that contains it
 
 error[E0401]: can't use generic parameters from outer item
@@ -22,6 +23,7 @@ LL |     static a: *const T = Default::default();
    |            |
    |            generic parameter used in this inner static item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `static` is a separate item from the item that contains it
 
 error[E0401]: can't use generic parameters from outer item
@@ -36,6 +38,7 @@ LL | |
 LL | |     }
    | |_____- generic parameter used in this inner extern block
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `static` is a separate item from the item that contains it
 
 error[E0401]: can't use generic parameters from outer item
@@ -48,6 +51,7 @@ LL |     static a: [u8; N] = [0; N];
    |            |
    |            generic parameter used in this inner static item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `static` is a separate item from the item that contains it
 
 error[E0401]: can't use generic parameters from outer item
@@ -60,6 +64,7 @@ LL |     static a: [u8; N] = [0; N];
    |            |
    |            generic parameter used in this inner static item
    |
+   = note: nested items are independent from their parent item for everything except for privacy and name resolution
    = note: a `static` is a separate item from the item that contains it
 
 error: aborting due to 5 previous errors