inference: fix union split handling for custom lattices#60857
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inference: fix union split handling for custom lattices#60857
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`MustAlias` has `has_extended_unionsplit(::MustAliasLattice) === true` so it is treated as a target for union split, but `uniontypes` does not handle `MustAlias` specially, causing union split to fail for `MustAlias`. This issue is addressed by always applying `uniontypes` to the result of `widenconst(x)`. External custom lattice implementations could previously provide their own `uniontypes`, but it would be cleaner interface design if they just overload `widenconst` for their custom lattice elements so that it returns `Union`-type.
aviatesk
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`MustAlias` has `has_extended_unionsplit(::MustAliasLattice) === true` so it is treated as a target for union split, but `uniontypes` does not handle `MustAlias` specially, causing union split to fail for `MustAlias`. This issue is addressed by always applying `uniontypes` to the result of `widenconst(x)`. External custom lattice implementations could previously provide their own `uniontypes`, but it would be cleaner interface design if they just overload `widenconst` for their custom lattice elements so that it returns `Union`-type.
aviatesk
added a commit
that referenced
this pull request
Jan 29, 2026
`MustAlias` has `has_extended_unionsplit(::MustAliasLattice) === true` so it is treated as a target for union split, but `uniontypes` does not handle `MustAlias` specially, causing union split to fail for `MustAlias`. This issue is addressed by always applying `uniontypes` to the result of `widenconst(x)`. External custom lattice implementations could previously provide their own `uniontypes`, but it would be cleaner interface design if they just overload `widenconst` for their custom lattice elements so that it returns `Union`-type.
aviatesk
removed
backport 1.12
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MustAliashashas_extended_unionsplit(::MustAliasLattice) === trueso it is treated as a target for union split, butuniontypesdoes not handleMustAliasspecially, causing union split to fail forMustAlias.This issue is addressed by always applying
uniontypesto the result ofwidenconst(x).External custom lattice implementations could previously provide their own
uniontypes, but it would be cleaner interface design if they just overloadwidenconstfor their custom lattice elements so that it returnsUnion-type.