Note that type param is chosen by caller when suggesting return impl Trait

jieyouxu · sladyn98 · kvverti · jieyouxu · commit a29ac16401ec · 2024-03-08T19:11:35.000Z
Revives #112088 and #104755. Co-authored-by: sladynnunes <snunes@usc.edu> Co-authored-by: Thalia Nero <chrisvn00@gmail.com>
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
@@ -889,7 +889,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             self.dcx(),
                             errors::ExpectedReturnTypeLabel::Other { span: hir_ty.span, expected },
                         );
-                        self.try_suggest_return_impl_trait(err, expected, ty, fn_id);
+                        self.try_suggest_return_impl_trait(err, expected, found, fn_id);
                         return true;
                     }
                 }
@@ -1010,6 +1010,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             format!("impl {all_bounds_str}"),
             Applicability::MaybeIncorrect,
         );
+
+        err.note(format!(
+            "the caller chooses a type for `{}` which can be different from `{}`",
+            expected_ty_as_param.name, found
+        ));
     }
 
     pub(in super::super) fn suggest_missing_break_or_return_expr(
diff --git a/tests/ui/return/return-impl-trait-bad.stderr b/tests/ui/return/return-impl-trait-bad.stderr
@@ -53,6 +53,7 @@ LL |     "don't suggest this, because the generic param is used in the bound."
    |
    = note: expected type parameter `T`
                    found reference `&'static str`
+   = note: the caller chooses a type for `T` which can be different from `&'static str`
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/return/return-impl-trait.stderr b/tests/ui/return/return-impl-trait.stderr
@@ -12,6 +12,7 @@ LL |     ()
    |
    = note: expected type parameter `T`
                    found unit type `()`
+   = note: the caller chooses a type for `T` which can be different from `()`
 
 error[E0308]: mismatched types
   --> $DIR/return-impl-trait.rs:23:5
@@ -28,6 +29,7 @@ LL |     ()
    |
    = note: expected type parameter `T`
                    found unit type `()`
+   = note: the caller chooses a type for `T` which can be different from `()`
 
 error: aborting due to 2 previous errors
 

Original file line number	Diff line number	Diff line change
`@@ -889,7 +889,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {`
`889`	`889`	`self.dcx(),`
`890`	`890`	`errors::ExpectedReturnTypeLabel::Other { span: hir_ty.span, expected },`
`891`	`891`	`);`
`892`		`- self.try_suggest_return_impl_trait(err, expected, ty, fn_id);`
	`892`	`+ self.try_suggest_return_impl_trait(err, expected, found, fn_id);`
`893`	`893`	`return true;`
`894`	`894`	`}`
`895`	`895`	`}`
`@@ -1010,6 +1010,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {`
`1010`	`1010`	`format!("impl {all_bounds_str}"),`
`1011`	`1011`	`Applicability::MaybeIncorrect,`
`1012`	`1012`	`);`
	`1013`	`+`
	`1014`	`+ err.note(format!(`
	`1015`	+ "the caller chooses a type for `{}` which can be different from `{}`",
	`1016`	`+ expected_ty_as_param.name, found`
	`1017`	`+ ));`
`1013`	`1018`	`}`
`1014`	`1019`
`1015`	`1020`	`pub(in super::super) fn suggest_missing_break_or_return_expr(`
Original file line number	Diff line number	Diff line change
`@@ -53,6 +53,7 @@ LL \| "don't suggest this, because the generic param is used in the bound."`
`53`	`53`	`\|`
`54`	`54`	= note: expected type parameter `T`
`55`	`55`	found reference `&'static str`
	`56`	+ = note: the caller chooses a type for `T` which can be different from `&'static str`
`56`	`57`
`57`	`58`	`error: aborting due to 4 previous errors`
`58`	`59`
Original file line number	Diff line number	Diff line change
`@@ -12,6 +12,7 @@ LL \| ()`
`12`	`12`	`\|`
`13`	`13`	= note: expected type parameter `T`
`14`	`14`	found unit type `()`
	`15`	+ = note: the caller chooses a type for `T` which can be different from `()`
`15`	`16`
`16`	`17`	`error[E0308]: mismatched types`
`17`	`18`	`--> $DIR/return-impl-trait.rs:23:5`
`@@ -28,6 +29,7 @@ LL \| ()`
`28`	`29`	`\|`
`29`	`30`	= note: expected type parameter `T`
`30`	`31`	found unit type `()`
	`32`	+ = note: the caller chooses a type for `T` which can be different from `()`
`31`	`33`
`32`	`34`	`error: aborting due to 2 previous errors`
`33`	`35`