[PEP 695] Support recursive type aliases #17268
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ilevkivskyi
approved these changes
May 20, 2024
mypy/semanal.py
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| # for a TypeInfo _in place_ if there are nested placeholders. | ||
| existing.node.target = res | ||
| existing.node.alias_tvars = alias_tvars | ||
| # existing.node.no_args = no_args |
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Why is this commented out? IIRC this is to support prehistoric edge case where you have
A = B
B = C
C = Dand D is generic class. In such cases A[int] is allowed and equivalent to D[int]. If this works without this line then just delete it. (Or maybe this use case is explicitly prohibited with the new syntax, then I guess this is not needed either). For context, IIRC this was initially allowed for aliases like List = list + forward references.
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This is not supported by the new syntax. Type parameters need to be explicit. I will delete the line.
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
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The implementation follows the approach used for old-style type aliases.
Work on #15238.