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Auto merge of #138249 - compiler-errors:auto-self, r=lcnr

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Do not register `Self: AutoTrait` when confirming auto trait (in old solver)

Every built-in auto impl for a trait goal like `Ty: Auto` immediately registers another obligation of `Ty: Auto` as one of its nested obligations, leading to us stressing the cycle detection machinery a lot more than we need to. This is because all traits have a `Self: Trait` predicate.

To fix this, remove the call to `impl_or_trait_obligations` in `vtable_auto_impl`, since auto traits do not have where clauses.

r? lcnr
This commit is contained in:
bors 2025-03-13 05:37:55 +00:00
commit 961351c76c
3 changed files with 4 additions and 43 deletions
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16
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
View file

@ -463,18 +463,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let cause = obligation.derived_cause(ObligationCauseCode::BuiltinDerived);
assert_eq!(obligation.predicate.polarity(), ty::PredicatePolarity::Positive);
let trait_ref =
self.infcx.enter_forall_and_leak_universe(obligation.predicate).trait_ref;
let trait_obligations = self.impl_or_trait_obligations(
&cause,
obligation.recursion_depth + 1,
obligation.param_env,
trait_def_id,
trait_ref.args,
obligation.predicate,
);
let mut obligations = self.collect_predicates_for_types(
let obligations = self.collect_predicates_for_types(
obligation.param_env,
cause,
obligation.recursion_depth + 1,
@ -482,10 +472,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
nested,
);
// Adds the predicates from the trait. Note that this contains a `Self: Trait`
// predicate as usual. It won't have any effect since auto traits are coinductive.
obligations.extend(trait_obligations);
debug!(?obligations, "vtable_auto_impl");
obligations

2
tests/ui/traits/inductive-overflow/supertrait-auto-trait.rs
View file

@ -13,6 +13,6 @@ fn copy<T: Magic>(x: T) -> (T, T) { (x, x) }
struct NoClone;
fn main() {
let (a, b) = copy(NoClone); //~ ERROR
let (a, b) = copy(NoClone);
println!("{:?} {:?}", a, b);
}

29
tests/ui/traits/inductive-overflow/supertrait-auto-trait.stderr
View file

@ -6,31 +6,6 @@ LL | auto trait Magic: Copy {}
| |
| auto traits cannot have super traits or lifetime bounds
error[E0277]: the trait bound `NoClone: Magic` is not satisfied
--> $DIR/supertrait-auto-trait.rs:16:23
|
LL | let (a, b) = copy(NoClone);
| ---- ^^^^^^^ the trait `Copy` is not implemented for `NoClone`
| |
| required by a bound introduced by this call
|
note: required for `NoClone` to implement `Magic`
--> $DIR/supertrait-auto-trait.rs:8:12
|
LL | auto trait Magic: Copy {}
| ^^^^^
note: required by a bound in `copy`
--> $DIR/supertrait-auto-trait.rs:10:12
|
LL | fn copy<T: Magic>(x: T) -> (T, T) { (x, x) }
| ^^^^^ required by this bound in `copy`
help: consider annotating `NoClone` with `#[derive(Copy)]`
|
LL + #[derive(Copy)]
LL | struct NoClone;
|
error: aborting due to 1 previous error
error: aborting due to 2 previous errors
Some errors have detailed explanations: E0277, E0568.
For more information about an error, try `rustc --explain E0277`.
For more information about this error, try `rustc --explain E0568`.