[ty] Add partial support for TypeIs
#18294
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InSyncWithFoo
requested review from
carljm,
AlexWaygood,
sharkdp and
dcreager
as code owners
|
|
Regarding the three problems outlined here:
This PR itself has two new issues:
|
|
Sorry, didn't realize there was a comment here looking for feedback. (In general I don't see draft PRs in my notifications, and I assume draft PRs are not ready for review, unless I'm pinged by name for comment.)
I think this is a feature, not a bug. The point of
Happy to dig into this tomorrow, if this is the only issue blocking this PR. |
|
@carljm Actually, I think I got them:
The only blocking problem left is that the fuzzer says this PR causes new panics. Here's the generated snippet: for name_3 in something:
class name_5[**name_4](name_3):
pass
else:
class name_3[name_5](b'', name_5=name_1):
pass
name_5()
for name_2 in something:
pass
else:
@name_3
def name_3():
pass
(name_3 := f'') and (name_1 := name_2)
assert name_3I reckon this has something to do with the Otherwise, this is ready for review. |
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Summary
Redo of #16314, part of #117.
TypeIs[]is a special form that allows users to define their own narrowing functions. Despite the syntax,TypeIsis not a generic and, on its own, it is meaningless as a type. Officially, a function annotated as returning aTypeIs[T]is a type narrowing function, whereTis called theTypeIsreturn type.A
TypeIs[T]may or may not be bound to a symbol. Only bound types have narrowing effect:A
TypeIs[T]type:Tis fully static.TrueandFalse.In other words, an unbound type have ambiguous truthiness.
It is possible to infer more precise truthiness for bound types; however, that is not part of this change.
TypeIs[T]is a subtype of or otherwise assignable tobool.TypeIsis invariant with respect to theTypeIsreturn type:TypeIs[int]is neither a subtype nor a supertype ofTypeIs[bool]. When ty sees a function marked as returningTypeIs[T], itsreturns will be checked againstboolinstead. ty will also report such functions if they don't accept a positional argument. Addtionally, a type narrowing function call with no positional arguments (e.g.,f()in the example above) will be considered invalid.Test Plan
Markdown tests.