trait_solver: Reject canonical responses with placeholder universe leaks - #160955
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trait_solver: Reject canonical responses with placeholder universe leaks#160955Dnreikronos wants to merge 5 commits into
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Cover opaque returns of `impl for<T> Trait<T>` under -Zassumptions-on-binders so proof-tree replay no longer ICEs on placeholder universe mismatches.
Proof-tree visitors previously treated instantiate_nested_goals failure as a successful visit via VisitorResult::output(), which is Continue for ControlFlow. CoerceVisitor must Break instead so coerce_unsized rejects inapplicable candidate replay rather than treating it as a valid unsizing path.
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Some changes occurred to the core trait solver cc @rust-lang/initiative-trait-system-refactor |
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r? @folkertdev rustbot has assigned @folkertdev. Use Why was this reviewer chosen?The reviewer was selected based on:
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r? @BoxyUwU for assumptions on binders stuff |
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Fixes #160802
-Zassumptions-on-bindersplus animpl for<T> Trait<T>RPIT was ICEing in proof-tree replay whenunify_query_var_valueshit.unwrap()on a Sorts error for the same binder placeholder living in two universes. Imo that unwrap was always a bit cursed on the diagnostics path, idk why we kept trusting it this long.Canonical response/state apply is fallible now and turns those leaks into
NoSolutioninstead of panicking. Region-only placeholders don't block valid region lowering. Also madeCoerceVisitorBreak when nested candidate replay fails, since Continue was treating a failed instantiate as "unsizing ok" (btwVisitorResult::outputis Continue forControlFlow, easy to miss). Added the issue repro plus a few universe-leak regressions.Fyi the
prev_universeproof-tree fix is already on main and I kept it. Irl I'd rather get this in asap than bike-shed the diagnostics wording further, but ltm if you'd rather the failed replay surface louder than a quietNoSolution.