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Rollup merge of #104269 - compiler-errors:hang-in-where-clause-sugg, r=lcnr

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Fix hang in where-clause suggestion with `predicate_can_apply`

Using `predicate_may_hold` during error reporting causes an evaluation overflow, which (because we use `evaluate_obligation_no_overflow`) then causes the predicate to need to be re-evaluated locally, which results in a hang.

... but since the "add a where clause" suggestion is best-effort, just throw any overflow errors. No need for 100% accuracy.

r? `@lcnr` who has been thinking about overflows... Let me know if you want more context about this issue, and as always, feel free to reassign.

Fixes #104225
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Dylan DPC 2022-11-23 20:32:35 +05:30 • committed by GitHub
commit bd91c94a5d
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6 changed files with 74 additions and 4 deletions
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5
compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
View file

@ -2546,7 +2546,10 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
let obligation =
Obligation::new(self.tcx, ObligationCause::dummy(), param_env, cleaned_pred);
self.predicate_may_hold(&obligation)
// We don't use `InferCtxt::predicate_may_hold` because that
// will re-run predicates that overflow locally, which ends up
// taking a really long time to compute.
self.evaluate_obligation(&obligation).map_or(false, |eval| eval.may_apply())
})
}

5
compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
View file

@ -1340,9 +1340,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
obligation.param_env,
trait_pred_and_suggested_ty,
);
let suggested_ty_would_satisfy_obligation = self
.evaluate_obligation_no_overflow(&new_obligation)
.must_apply_modulo_regions();
let suggested_ty_would_satisfy_obligation =
self.predicate_must_hold_modulo_regions(&new_obligation);
if suggested_ty_would_satisfy_obligation {
let sp = self
.tcx