Point at a type parameter shadowing another type

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -161,6 +161,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
             msg: String,
             fallback_label: String,
             span: Span,
+            span_label: Option<(Span, &'a str)>,
             could_be_expr: bool,
             suggestion: Option<(Span, &'a str, String)>,
         }
@@ -172,6 +173,12 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                 msg: format!("expected {}, found {} `{}`", expected, res.descr(), path_str),
                 fallback_label: format!("not a {expected}"),
                 span,
+                span_label: match res {
+                    Res::Def(kind, def_id) if kind == DefKind::TyParam => {
+                        self.def_span(def_id).map(|span| (span, "found this type pararmeter"))
+                    }
+                    _ => None,
+                },
                 could_be_expr: match res {
                     Res::Def(DefKind::Fn, _) => {
                         // Verify whether this is a fn call or an Fn used as a type.
@@ -251,6 +258,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                     format!("not found in {mod_str}")
                 },
                 span: item_span,
+                span_label: None,
                 could_be_expr: false,
                 suggestion,
             }
@@ -262,6 +270,10 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 
         self.suggest_swapping_misplaced_self_ty_and_trait(&mut err, source, res, base_error.span);
 
+        if let Some((span, label)) = base_error.span_label {
+            err.span_label(span, label);
+        }
+
         if let Some(sugg) = base_error.suggestion {
             err.span_suggestion_verbose(sugg.0, sugg.1, sugg.2, Applicability::MaybeIncorrect);
         }

src/test/ui/const-generics/generic_const_exprs/issue-69654.stderr

@@ -2,7 +2,9 @@ error[E0423]: expected value, found type parameter `T`
   --> $DIR/issue-69654.rs:5:25
    |
 LL | impl<T> Bar<T> for [u8; T] {}
-   |                         ^ not a value
+   |      -                  ^ not a value
+   |      |
+   |      found this type pararmeter
 
 error[E0599]: the function or associated item `foo` exists for struct `Foo<_>`, but its trait bounds were not satisfied
   --> $DIR/issue-69654.rs:17:10

src/test/ui/lexical-scopes.stderr

@@ -1,6 +1,8 @@
 error[E0574]: expected struct, variant or union type, found type parameter `T`
   --> $DIR/lexical-scopes.rs:3:13
    |
+LL | fn f<T>() {
+   |      - found this type pararmeter
 LL |     let t = T { i: 0 };
    |             ^ not a struct, variant or union type
 

src/test/ui/resolve/point-at-type-parameter-shadowing-another-type.rs

@@ -0,0 +1,21 @@
+trait Foo<T> {
+    fn foo(&self, name: T) -> usize;
+}
+
+struct Bar {
+    baz: Baz,
+}
+
+struct Baz {
+    num: usize,
+}
+
+impl<Baz> Foo<Baz> for Bar {
+    fn foo(&self, _name: Baz) -> usize {
+        match self.baz {
+            Baz { num } => num, //~ ERROR expected struct, variant or union type, found type parameter `Baz`
+        }
+    }
+}
+
+fn main() {}

src/test/ui/resolve/point-at-type-parameter-shadowing-another-type.stderr

@@ -0,0 +1,12 @@
+error[E0574]: expected struct, variant or union type, found type parameter `Baz`
+  --> $DIR/point-at-type-parameter-shadowing-another-type.rs:16:13
+   |
+LL | impl<Baz> Foo<Baz> for Bar {
+   |      --- found this type pararmeter
+...
+LL |             Baz { num } => num,
+   |             ^^^ not a struct, variant or union type
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0574`.

src/test/ui/span/issue-35987.stderr

@@ -2,7 +2,9 @@ error[E0404]: expected trait, found type parameter `Add`
   --> $DIR/issue-35987.rs:5:21
    |
 LL | impl<T: Clone, Add> Add for Foo<T> {
-   |                     ^^^ not a trait
+   |                ---  ^^^ not a trait
+   |                |
+   |                found this type pararmeter
    |
 help: consider importing this trait instead
    |

src/tools/rust-analyzer/bench_data/glorious_old_parser

@@ -1988,7 +1988,7 @@ impl<'a> Parser<'a> {
                     err.span_suggestion(
                         span,
                         "declare the type after the parameter binding",
-                        String::from("<identifier>: <type>"),
+                        "<identifier>: <type>",
                         Applicability::HasPlaceholders,
                     );
                 } else if require_name && is_trait_item {