Constrain const vars to error if const types are mismatched #109336
Merged
+51
−13
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When equating two consts of different types, if either are const variables, constrain them to the correct const error kind.
This helps us avoid "successfully" matching a const against an impl signature but leaving unconstrained const vars, which will lead to incremental ICEs when we call const-eval queries during const projection.
Fixes #109296
The second commit in the stack fixes a regression in the first commit where we end up mentioning
[const error]
in an impl overlap error message. I think the error message changes for the better, but I could implement alternative strategies to avoid this without delaying the overlap error message...r? @BoxyUwU