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

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

2 files changed, 6 insertions, 4 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index ef3d300020a..f9f80f9d58c 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -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())
         })
     }
 
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 186109e7075..bb6d7d0e8df 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -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