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Unrolled build for rust-lang#126558
Rollup merge of rust-lang#126558 - jieyouxu:caller-chooses-ty, r=fmease hir_typeck: be more conservative in making "note caller chooses ty param" note In rust-lang#122195 I added a "caller chooses ty for type param" note for when the return expression type a.k.a. found type does not match the expected return type. rust-lang#126547 found that this note was confusing when the found return type *contains* the expected type, e.g. ```rs fn f<T>(t: &T) -> T { t } ``` because the found return type `&T` will *always* be different from the expected return type `T`, so the note was needlessly redundant and confusing. This PR addresses that by not making the note if the found return type contains the expected return type. r? ``@fmease`` (since you reviewed the original PR) Fixes rust-lang#126547
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‎compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

+22-10
Original file line numberDiff line numberDiff line change
@@ -859,10 +859,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
859859
} else {
860860
// Only point to return type if the expected type is the return type, as if they
861861
// are not, the expectation must have been caused by something else.
862-
debug!("return type {:?}", hir_ty);
862+
debug!(?hir_ty, "return type");
863863
let ty = self.lowerer().lower_ty(hir_ty);
864-
debug!("return type {:?}", ty);
865-
debug!("expected type {:?}", expected);
864+
debug!(?ty, "return type (lowered)");
865+
debug!(?expected, "expected type");
866866
let bound_vars = self.tcx.late_bound_vars(hir_ty.hir_id.owner.into());
867867
let ty = Binder::bind_with_vars(ty, bound_vars);
868868
let ty = self.normalize(hir_ty.span, ty);
@@ -873,7 +873,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
873873
expected,
874874
});
875875
self.try_suggest_return_impl_trait(err, expected, found, fn_id);
876-
self.note_caller_chooses_ty_for_ty_param(err, expected, found);
876+
self.try_note_caller_chooses_ty_for_ty_param(err, expected, found);
877877
return true;
878878
}
879879
}
@@ -883,18 +883,30 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
883883
false
884884
}
885885

886-
fn note_caller_chooses_ty_for_ty_param(
886+
fn try_note_caller_chooses_ty_for_ty_param(
887887
&self,
888888
diag: &mut Diag<'_>,
889889
expected: Ty<'tcx>,
890890
found: Ty<'tcx>,
891891
) {
892-
if let ty::Param(expected_ty_as_param) = expected.kind() {
893-
diag.subdiagnostic(errors::NoteCallerChoosesTyForTyParam {
894-
ty_param_name: expected_ty_as_param.name,
895-
found_ty: found,
896-
});
892+
// Only show the note if:
893+
// 1. `expected` ty is a type parameter;
894+
// 2. The `expected` type parameter does *not* occur in the return expression type. This can
895+
// happen for e.g. `fn foo<T>(t: &T) -> T { t }`, where `expected` is `T` but `found` is
896+
// `&T`. Saying "the caller chooses a type for `T` which can be different from `&T`" is
897+
// "well duh" and is only confusing and not helpful.
898+
let ty::Param(expected_ty_as_param) = expected.kind() else {
899+
return;
900+
};
901+
902+
if found.contains(expected) {
903+
return;
897904
}
905+
906+
diag.subdiagnostic(errors::NoteCallerChoosesTyForTyParam {
907+
ty_param_name: expected_ty_as_param.name,
908+
found_ty: found,
909+
});
898910
}
899911

900912
/// check whether the return type is a generic type with a trait bound

‎tests/ui/return/return-ty-mismatch-note.rs

+10-1
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
1-
// Checks existence of a note for "a caller chooses ty for ty param" upon return ty mismatch.
1+
// Checks existence or absence of a note for "a caller chooses ty for ty param" upon return ty
2+
// mismatch.
23

34
fn f<T>() -> (T,) {
45
(0,) //~ ERROR mismatched types
@@ -14,6 +15,14 @@ fn h() -> u8 {
1415
0u8
1516
}
1617

18+
// This case was reported in <https://github.com/rust-lang/rust/issues/126547> where it doesn't
19+
// make sense to make the "note caller chooses ty for ty param" note if the found type contains
20+
// the ty param...
21+
fn k<T>(_t: &T) -> T {
22+
_t
23+
//~^ ERROR mismatched types
24+
}
25+
1726
fn main() {
1827
f::<()>();
1928
g::<(), ()>;

‎tests/ui/return/return-ty-mismatch-note.stderr

+17-4
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
error[E0308]: mismatched types
2-
--> $DIR/return-ty-mismatch-note.rs:4:6
2+
--> $DIR/return-ty-mismatch-note.rs:5:6
33
|
44
LL | fn f<T>() -> (T,) {
55
| - expected this type parameter
@@ -10,7 +10,7 @@ LL | (0,)
1010
found type `{integer}`
1111

1212
error[E0308]: mismatched types
13-
--> $DIR/return-ty-mismatch-note.rs:8:6
13+
--> $DIR/return-ty-mismatch-note.rs:9:6
1414
|
1515
LL | fn g<U, V>() -> (U, V) {
1616
| - expected this type parameter
@@ -21,7 +21,7 @@ LL | (0, "foo")
2121
found type `{integer}`
2222

2323
error[E0308]: mismatched types
24-
--> $DIR/return-ty-mismatch-note.rs:8:9
24+
--> $DIR/return-ty-mismatch-note.rs:9:9
2525
|
2626
LL | fn g<U, V>() -> (U, V) {
2727
| - expected this type parameter
@@ -31,6 +31,19 @@ LL | (0, "foo")
3131
= note: expected type parameter `V`
3232
found reference `&'static str`
3333

34-
error: aborting due to 3 previous errors
34+
error[E0308]: mismatched types
35+
--> $DIR/return-ty-mismatch-note.rs:22:5
36+
|
37+
LL | fn k<T>(_t: &T) -> T {
38+
| - - expected `T` because of return type
39+
| |
40+
| expected this type parameter
41+
LL | _t
42+
| ^^ expected type parameter `T`, found `&T`
43+
|
44+
= note: expected type parameter `_`
45+
found reference `&_`
46+
47+
error: aborting due to 4 previous errors
3548

3649
For more information about this error, try `rustc --explain E0308`.

‎tests/ui/suggestions/clone-on-unconstrained-borrowed-type-param.stderr

-1
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,6 @@ LL | t.clone()
1010
|
1111
= note: expected type parameter `_`
1212
found reference `&_`
13-
= note: the caller chooses a type for `T` which can be different from `&T`
1413
note: `T` does not implement `Clone`, so `&T` was cloned instead
1514
--> $DIR/clone-on-unconstrained-borrowed-type-param.rs:3:5
1615
|

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