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Make sure to ignore elided lifetimes when pointing at args for fulfillment errors #132935

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Nov 12, 2024
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Make sure to ignore elided lifetimes when pointing at args for fulfillment errors #132935

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20 changes: 16 additions & 4 deletions compiler/rustc_hir_typeck/src/fn_ctxt/adjust_fulfillment_errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -316,12 +316,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
.tcx
.generics_of(def_id)
.own_args(ty::GenericArgs::identity_for_item(self.tcx, def_id));
let Some((index, _)) =
own_args.iter().enumerate().find(|(_, arg)| **arg == param_to_point_at)
else {
let Some(mut index) = own_args.iter().position(|arg| *arg == param_to_point_at) else {
return false;
};
let Some(arg) = segment.args().args.get(index) else {
// SUBTLE: We may or may not turbofish lifetime arguments, which will
// otherwise be elided. if our "own args" starts with a lifetime, but
// the args list does not, then we should chop off all of the lifetimes,
// since they're all elided.
let segment_args = segment.args().args;
if matches!(own_args[0].unpack(), ty::GenericArgKind::Lifetime(_))
&& segment_args.first().is_some_and(|arg| arg.is_ty_or_const())
&& let Some(offset) = own_args.iter().position(|arg| {
matches!(arg.unpack(), ty::GenericArgKind::Type(_) | ty::GenericArgKind::Const(_))
})
&& let Some(new_index) = index.checked_sub(offset)
{
index = new_index;
}
let Some(arg) = segment_args.get(index) else {
return false;
};
error.obligation.cause.span = arg
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4 changes: 2 additions & 2 deletions tests/ui/associated-types/hr-associated-type-bound-param-3.stderr
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Expand Up @@ -15,10 +15,10 @@ LL | for<'b> <T as X<'b, T>>::U: Clone,
| ^^^^^ required by this bound in `X`

error[E0277]: the trait bound `str: Clone` is not satisfied
--> $DIR/hr-associated-type-bound-param-3.rs:18:5
--> $DIR/hr-associated-type-bound-param-3.rs:18:18
|
LL | <(i32,) as X<(i32,)>>::f("abc");
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This is a great example of the bug. We have X<'a, T> above, but have only specified the type parameter. Since we were basically trying to index at 1 into a list of 1, we would fail. Now we properly adjust the index to account for the lifetime not being there :D

| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `str`
| ^^^^^^ the trait `Clone` is not implemented for `str`
|
= help: the trait `Clone` is implemented for `String`
note: required by a bound in `X::f`
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4 changes: 2 additions & 2 deletions tests/ui/associated-types/hr-associated-type-bound-param-4.stderr
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Expand Up @@ -15,10 +15,10 @@ LL | for<'b> <(T,) as X<'b, T>>::U: Clone,
| ^^^^^ required by this bound in `X`

error[E0277]: the trait bound `str: Clone` is not satisfied
--> $DIR/hr-associated-type-bound-param-4.rs:18:5
--> $DIR/hr-associated-type-bound-param-4.rs:18:18
|
LL | <(i32,) as X<i32>>::f("abc");
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `str`
| ^^^ the trait `Clone` is not implemented for `str`
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This feels like a worse error? The carets point to i32 but the text talks about str, feels very confusing.

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This is a preexisting consequence of the algorithm. I'm just fixing an off-by-N bug.

|
= help: the trait `Clone` is implemented for `String`
note: required by a bound in `X::f`
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4 changes: 2 additions & 2 deletions tests/ui/associated-types/hr-associated-type-bound-param-5.stderr
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Expand Up @@ -31,10 +31,10 @@ LL | for<'b> <T::Next as X<'b, T::Next>>::U: Clone,
| ^^^^^ required by this bound in `X`

error[E0277]: the trait bound `str: Clone` is not satisfied
--> $DIR/hr-associated-type-bound-param-5.rs:36:5
--> $DIR/hr-associated-type-bound-param-5.rs:36:15
|
LL | <i32 as X<Box<i32>>>::f("abc");
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `str`
| ^^^^^^^^ the trait `Clone` is not implemented for `str`
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ditto

|
= help: the trait `Clone` is implemented for `String`
note: required by a bound in `X::f`
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1 change: 1 addition & 0 deletions tests/ui/associated-types/hr-associated-type-bound-param-6.rs
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Expand Up @@ -17,5 +17,6 @@ impl<S, T> X<'_, T> for (S,) {
pub fn main() {
<(i32,) as X<i32>>::f("abc");
//~^ ERROR the trait bound `for<'b> i32: X<'b, i32>` is not satisfied
//~| ERROR the trait bound `for<'b> i32: X<'b, i32>` is not satisfied
//~| ERROR the trait bound `i32: X<'_, i32>` is not satisfied
}
18 changes: 17 additions & 1 deletion tests/ui/associated-types/hr-associated-type-bound-param-6.stderr
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Expand Up @@ -17,6 +17,22 @@ LL | <(i32,) as X<i32>>::f("abc");
|
= help: the trait `X<'_, T>` is implemented for `(S,)`

error[E0277]: the trait bound `for<'b> i32: X<'b, i32>` is not satisfied
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@compiler-errors compiler-errors Nov 12, 2024 •
edited
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We have a duplicated error here b/c we can only refine one of two copies of this fulfillment error: one that comes from well-formedness, and one that comes from the predicates_of query.

I think it's fine to ignore this regression, since it's a net improvement for other errors.

--> $DIR/hr-associated-type-bound-param-6.rs:18:18
|
LL | <(i32,) as X<i32>>::f("abc");
| ^^^ the trait `for<'b> X<'b, i32>` is not implemented for `i32`
|
= help: the trait `X<'_, T>` is implemented for `(S,)`
note: required by a bound in `X::f`
--> $DIR/hr-associated-type-bound-param-6.rs:3:16
|
LL | for<'b> T: X<'b, T>,
| ^^^^^^^^ required by this bound in `X::f`
...
LL | fn f(x: &<T as X<'_, T>>::U) {
| - required by a bound in this associated function

error[E0277]: the trait bound `i32: X<'_, i32>` is not satisfied
--> $DIR/hr-associated-type-bound-param-6.rs:18:27
|
Expand All @@ -25,6 +41,6 @@ LL | <(i32,) as X<i32>>::f("abc");
|
= help: the trait `X<'_, T>` is implemented for `(S,)`

error: aborting due to 3 previous errors
error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0277`.
4 changes: 2 additions & 2 deletions tests/ui/higher-ranked/leak-check/candidate-from-env-universe-err-2.next.stderr
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@@ -1,8 +1,8 @@
error[E0277]: the trait bound `for<'a> T: Trait<'a, '_>` is not satisfied
--> $DIR/candidate-from-env-universe-err-2.rs:15:5
--> $DIR/candidate-from-env-universe-err-2.rs:15:15
|
LL | impl_hr::<T>();
| ^^^^^^^^^^^^^^ the trait `for<'a> Trait<'a, '_>` is not implemented for `T`
| ^ the trait `for<'a> Trait<'a, '_>` is not implemented for `T`
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This one is better, the carets point to T which matches the error text.

|
note: required by a bound in `impl_hr`
--> $DIR/candidate-from-env-universe-err-2.rs:12:19
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