Don't simplify out ErasedType from unions during type inference #8095
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JukkaL
approved these changes
Dec 5, 2019
test-data/unit/check-inference.test
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| x: Optional[str] | ||
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| pagelets = filter(None, [x]) |
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Test that the type of pagelets is List[str]?
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Fixes #8093
The fix is kind of simple, we really need to keep all
ErasedTypes intact to preserve the existing type inference logic, but it is also long because I need to thread the flag down like dozen function calls.The issue itself btw highlight how fragile is current type inference logic (note that
expand_type()implicitly callsmake_simplified_union()too, but I think that one doesn't need to be updated because it shouldn't be called with any erased components).