New semantic analyzer: fix recursive type aliases #7091
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This fixes maximum iteration count errors. Recursive type aliases still don't work and the behavior is a regression from the old semantic analyzer. Previously they were truncated, but now they aren't supported at all. We could perhaps hack something similar to what we used to have, but I don't think that it's urgent. This also breaks some use cases where "semi-recursive" type aliases were supported previously. The support mechanism caused infinite expansion for actual recursive type aliases. I couldn't come up with a simple way to support both, so I decided to prioritize fixing infinite expansion, as they have a worse impact on user experience. Work towards #6445.
ilevkivskyi
approved these changes
Jun 28, 2019
| @@ -2347,7 +2347,7 @@ def check_and_set_up_type_alias(self, s: AssignmentStmt) -> bool: | |||
| self.analyze_alias(rvalue, allow_placeholder=True) | |||
| if not res: | |||
| return False | |||
| if self.found_incomplete_ref(tag) or isinstance(res, PlaceholderType): | |||
| if self.found_incomplete_ref(tag) or has_placeholder(res): | |||
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Please add a comment that we should only prohibit top-level placeholders as in base classes and NewTypes in long term, and this is a temporary measure.
| main:4: error: Cannot resolve name "B" (possible cyclic definition) | ||
| main:4: error: Cannot resolve name "C" (possible cyclic definition) | ||
| main:7: note: Revealed type is 'Any' | ||
| main:8: note: Revealed type is 'Any' |
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It looks like all new failures in this file are because of the problem with nested placeholders. Please add a comment in the existing issue mentioning this, and add links to the issue in these tests.
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Added new issues about this: #7111
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This fixes maximum iteration count errors.
Recursive type aliases still don't work and the behavior is a
regression from the old semantic analyzer. Previously they were
truncated, but now they aren't supported at all. We could perhaps hack
something similar to what we used to have, but I don't think that it's
urgent.
This also breaks some use cases where "semi-recursive" type aliases
were supported previously. The support mechanism caused infinite
expansion for actual recursive type aliases. I couldn't come up with a
simple way to support both, so I decided to prioritize fixing infinite
expansion, as they have a worse impact on user experience.
Work towards #6445.