Rollup merge of rust-lang#148447 - estebank:outer-param-2, r=jackh726

Tweak E0401

More accurate span pointing at use place of outer param (at ident instead of full path).

Add note explaining why outer item params can't be used in inner item.

Use structured suggestion for what `Self` should have been.

Follow up to rust-lang#148370.

Fix rust-lang#37892.

Author: matthiaskrgr

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