Fix MRO shadowing of VariantLikeType.add_classes#331
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alexcrichton merged 1 commit intobytecodealliance:mainfrom Apr 3, 2026
Merged
Fix MRO shadowing of VariantLikeType.add_classes#331alexcrichton merged 1 commit intobytecodealliance:mainfrom
alexcrichton merged 1 commit intobytecodealliance:mainfrom
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Thanks! Would it be possible to add a test for this too? |
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VariantLikeType.add_classes is shadowed by ValType.add_classes in the MRO for VariantType, OptionType, and ResultType. ValType defines add_classes as abstract (no-op), and because it comes before VariantLikeType in C3 linearization, the real implementation never runs. This means tagged variants can't be passed as function arguments since add_classes returns an empty set, so the isinstance check in _lower always fails with "value not valid for this variant".
For example, passing a Variant("blah", Record(...)) into an option field always fails because the option's "some" case can't match the value.
The fix makes VariantLikeType inherit from ValType, then drops the now-redundant ValType from classes that get it through VariantLikeType. This puts VariantLikeType.add_classes before ValType.add_classes in the MRO. No other method resolution is affected since convert_to_c and convert_from_c are defined directly on the concrete classes.