Use full type when reporting a mismatch error #5833
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The leaf mismatch is the innermost piece of the type that failed to match, but that can occur after the type has been pulled apart multiple times. The full type is the entry point to the subtyping check, and is more likely to correspond to an actual code value.
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Yeah good call. That probably would be a good idea, but we can wait until that situation gets reported if you want; I'm thinking it'll be easier to come up with good verbiage given a concrete example |
aryairani
approved these changes
Aug 13, 2025
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The leaf mismatch is the innermost piece of the type that failed to match, but that can occur after the type has been pulled apart multiple times. The full type is the entry point to the subtyping check, and is more likely to correspond to an actual code value.
This fixes #5440. See the changed transcript output for a somewhat different example (where there the kinds made sense to talk about "a value" but there was actually no such value in the code). It might not be 100% guaranteed to never say something that sounds like a kind error, but it's less likely.
One thing I'm not sure about is if you have a really big subtyping call, it might be hard to spot the actual difference in the full types. So maybe I should still include the leaf mismatch with different verbage?