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add another type system invariant #2667

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add invariant
lcnr Dec 1, 2025
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Update src/solve/invariants.md
lcnr Dec 1, 2025
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6 changes: 6 additions & 0 deletions src/solve/invariants.md
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Expand Up @@ -116,6 +116,12 @@ We do however break this invariant in a few cases, some of which are due to bugs
- the builtin trait object trait implementation can overlap with a user-defined impl:
[#57893](https://github.com/rust-lang/rust/issues/57893)

### Goals with can be proven in a non-empty environment also hold during monomorphization ✅

If a goal can be proven in a generic environment, the goal should still hold after instantiating
it with fully concrete types and no where-clauses in scope.

This is assumed by codegen which ICEs when encountering non-overflow ambiguity. This invariant is currently broken by specialization ([#147507](https://github.com/rust-lang/rust/issues/147507)) and by marker traits ([#149502](https://github.com/rust-lang/rust/issues/149502)).

#### The type system is complete during the implicit negative overlap check in coherence ✅

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