8000 Fix crash on `ErasedType` and `covers_at_runtime` by sobolevn · Pull Request #11924 · python/mypy · GitHub
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Fix crash on ErasedType and covers_at_runtime #11924

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Merged
merged 5 commits into from
Jan 7, 2022
Merged

Fix crash on ErasedType and covers_at_runtime #11924

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83f40e7
Fix crash on `ErasedType` and `covers_at_runtime`, refs #11913
sobolevn Jan 6, 2022
ad5d73a
Fixes CI
sobolevn Jan 6, 2022
21ec5d4
Return `ErasedType` from `erase_type`
sobolevn Jan 6, 2022
13e1d8c
Merge branch 'master' into issue-11913
sobolevn Jan 6, 2022
3c3ecbb
Update test-data/unit/check-inference.test
sobolevn Jan 6, 2022
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Fixes CI
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@sobolevn
sobolevn committed Jan 6, 2022
commit ad5d73ae72eeb631e6f5d186d84b17cfe298bf7d
1 change: 1 addition & 0 deletions mypy/subtypes.py
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Expand Up @@ -1167,6 +1167,7 @@ def restrict_subtype_away(t: Type, s: Type, *, ignore_promotions: bool = False)
def covers_at_runtime(item: Type, supertype: Type, ignore_promotions: bool) -> bool:
"""Will isinstance(item, supertype) always return True at runtime?"""
item = get_proper_type(item)
supertype = get_proper_type(supertype)
if (isinstance(item, (ErasedType, DeletedType))
or isinstance(supertype, (ErasedType, DeletedType))):
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Hmm I wonder if ErasedType instances can be nested inside unions, for example, and still cause a crash. Maybe erase_type should just propagate erased types unmodified? I don't think that DeletedType can be nested so it seems safe to handle here, though I'm not sure we need special casing for it. Did you find a use case where we encounter deleted types here, or is it here more as a defensive measure?

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@sobolevn sobolevn Jan 6, 2022 •
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Hm, good idea. I will try it!

Did you find a use case where we encounter deleted types here, or is it here more as a defensive measure?

More like a defensive programming. I will remove it, because it does not make much sense without ErasedType.

# It might happen when working with `lambda` arguments.
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