Special case the situation where the previous span is the same as the new one

Author: oli-obk

compiler/rustc_typeck/src/collect/type_of.rs

@@ -639,7 +639,11 @@ fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
                             concrete_type.span,
                             format!("expected `{}`, got `{}`", prev.ty, concrete_type.ty),
                         );
-                        err.span_note(prev.span, "previous use here");
+                        if prev.span == concrete_type.span {
+                            err.span_label(prev.span, "this expression supplies two conflicting concrete types for the same opaque type");
+                        } else {
+                            err.span_note(prev.span, "previous use here");
+                        }
                         err.emit();
                     }
                 } else {

src/test/ui/impl-trait/issue-86465.stderr

@@ -1,14 +1,11 @@
 error: concrete type differs from previous defining opaque type use
   --> $DIR/issue-86465.rs:6:5
    |
-LL |     (a, a)
-   |     ^^^^^^ expected `&'a u32`, got `&'b u32`
-   |
-note: previous use here
-  --> $DIR/issue-86465.rs:6:5
-   |
 LL |     (a, a)
    |     ^^^^^^
+   |     |
+   |     expected `&'a u32`, got `&'b u32`
+   |     this expression supplies two conflicting concrete types for the same opaque type
 
 error: aborting due to previous error
 

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn-infer.stderr

@@ -1,14 +1,11 @@
 error: concrete type differs from previous defining opaque type use
   --> $DIR/multiple-def-uses-in-one-fn-infer.rs:10:5
    |
-LL |     (42_i64, 60)
-   |     ^^^^^^^^^^^^ expected `i64`, got `i32`
-   |
-note: previous use here
-  --> $DIR/multiple-def-uses-in-one-fn-infer.rs:10:5
-   |
 LL |     (42_i64, 60)
    |     ^^^^^^^^^^^^
+   |     |
+   |     expected `i64`, got `i32`
+   |     this expression supplies two conflicting concrete types for the same opaque type
 
 error: aborting due to previous error
 

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn-lifetimes.stderr

@@ -1,14 +1,11 @@
 error: concrete type differs from previous defining opaque type use
   --> $DIR/multiple-def-uses-in-one-fn-lifetimes.rs:6:5
    |
-LL |     (i, i)
-   |     ^^^^^^ expected `&'a i32`, got `&'b i32`
-   |
-note: previous use here
-  --> $DIR/multiple-def-uses-in-one-fn-lifetimes.rs:6:5
-   |
 LL |     (i, i)
    |     ^^^^^^
+   |     |
+   |     expected `&'a i32`, got `&'b i32`
+   |     this expression supplies two conflicting concrete types for the same opaque type
 
 error: aborting due to previous error
 

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn2.stderr

@@ -1,14 +1,11 @@
 error: concrete type differs from previous defining opaque type use
   --> $DIR/multiple-def-uses-in-one-fn2.rs:10:5
    |
-LL |     (a.clone(), a)
-   |     ^^^^^^^^^^^^^^ expected `A`, got `B`
-   |
-note: previous use here
-  --> $DIR/multiple-def-uses-in-one-fn2.rs:10:5
-   |
 LL |     (a.clone(), a)
    |     ^^^^^^^^^^^^^^
+   |     |
+   |     expected `A`, got `B`
+   |     this expression supplies two conflicting concrete types for the same opaque type
 
 error: aborting due to previous error