Make narrow_declared_type correctly handle Literal types
#6961
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This diff fixes the `narrowed_declared_type` function to correctly handle cases where the declared type is actually a `Literal[...]`. This fixes python#6952. In short, it seems like using the new semantic analyzer somehow made mypy call [the `narrow_type_from_binder(...)` function][0] where it previously did not. Specifically, mypy passed in the `var` expression and a `known_type` of `Literal[42]`, we got a restriction of `builtins.int` (with a `last_known_value` of 42), and attempted to narrow the `Literal[42]` on line 3512. But due to the missing case in `narrow_declared_type`, we ended up returning just the int. [0]: https://github.com/python/mypy/blob/master/mypy/checkexpr.py#L3504
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The difference in behavior is likely related to #6458, and the fact that Final gets "stripped" in the process. Although this fix works for the issue, I would like to actually understand why it happens before deciding whether we should use this as a fix.
Note there is a little merge conflict.
I'm not too familiar with the behavior of the new semantic analyzer, but fwiw it didn't seem as if this were the case. More precisely, it seemed we did correctly remember that the type of the variable was
I do think this fix would be useful independently from the linked issue. IIUC doing The fact that change fixes #6458 is almost a side-effect IMO. |
I mean this #6988. I still think this PR has value, but it might also mask an actual flaw in the logic in new semantic analyzer. |
This diff fixes the `narrowed_declared_type` function to correctly
handle cases where the declared type is actually a `Literal[...]`.
Specifically, doing something like the below will return `int` instead
of `Literal[42]`:
narrowed_declared_type(Literal[42], int)
This is inconsistent with the behavior of doing something like the
below, which will return `ChildType`:
narrowed_declared_type(ChildType, ParentType)
This diff modifies `narrowed_declared_type` to instead return `Literal[42]`
in the first example.
This diff fixes the
narrowed_declared_typefunction to correctly handle cases where the declared type is actually aLiteral[...].This fixes #6952.
In short, it seems like using the new semantic analyzer somehow made mypy call the
narrow_type_from_binder(...)function where it previously did not.Specifically, mypy passed in the
varexpression and aknown_typeofLiteral[42], we got a restriction ofbuiltins.int(with alast_known_valueof 42), and attempted to narrow theLiteral[42]on line 3512.But due to the missing case in
narrow_declared_type, we ended up returning just the int.