[ty] fix lazy snapshot sweeping in nested scopes #19908
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mtshiba
requested review from
AlexWaygood,
carljm,
dcreager and
sharkdp
as code owners
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Diagnostic diff on typing conformance testsChanges were detected when running ty on typing conformance tests--- old-output.txt 2025-08-14 06:00:34.776618614 +0000
+++ new-output.txt 2025-08-14 06:00:34.846619163 +0000
@@ -1,5 +1,5 @@
WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
-fatal[panic] Panicked at /home/runner/.cargo/git/checkouts/salsa-e6f3bb7c2a062968/918d35d/src/function/execute.rs:215:25 when checking `/home/runner/work/ruff/ruff/typing/conformance/tests/aliases_typealiastype.py`: `infer_definition_types(Id(1da61)): execute: too many cycle iterations`
+fatal[panic] Panicked at /home/runner/.cargo/git/checkouts/salsa-e6f3bb7c2a062968/918d35d/src/function/execute.rs:215:25 when checking `/home/runner/work/ruff/ruff/typing/conformance/tests/aliases_typealiastype.py`: `infer_definition_types(Id(50b5)): execute: too many cycle iterations`
_directives_deprecated_library.py:15:31: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `int`
_directives_deprecated_library.py:30:26: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
_directives_deprecated_library.py:36:41: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Self@__add__` |
Contributor
|
mtshiba
commented
Aug 14, 2025
| if x is not None: | ||
| def closure(): | ||
| reveal_type(x) # revealed: str | None | ||
| x = None |
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Author
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Upon closer analysis, it seems that whether or not narrowing is applied to x depends on whether the closure is exposed or just consumed in the scope (This PR does not take this into account and always assumes that the closure is exposed).
def f(x: str | None):
def _():
if x is not None:
def closure():
reveal_type(x) # revealed: str | None
return closure # expose a closure
x = None
def f(x: str | None):
def _():
if x is not None:
def closure():
reveal_type(x) # revealed: str
return closure() # just consume a closure
x = NoneTo achieve this, an additional mechanism would be required to determine whether a closure is exposed (pyright does not seem to implement this). This would likely be a future work.
Contributor
There was a problem hiding this comment.
Yes, I think in general we consider escape analysis for closures to be out of scope. Perhaps we could tackle it someday, but it's not needed now.
carljm
approved these changes
Aug 15, 2025
| if x is not None: | ||
| def closure(): | ||
| reveal_type(x) # revealed: str | None | ||
| x = None |
Contributor
There was a problem hiding this comment.
Yes, I think in general we consider escape analysis for closures to be out of scope. Perhaps we could tackle it someday, but it's not needed now.
dcreager
added a commit
that referenced
this pull request
Aug 15, 2025
* main: [ty] Represent `NamedTuple` as an opaque special form, not a class (#19915) [ty] Remove incorrect type narrowing for `if type(x) is C[int]` (#19926) Bump Rust MSRV to 1.87 (#19924) Add `else`-branch narrowing for `if type(a) is A` when `A` is `@final` (#19925) [ty] Sync vendored typeshed stubs (#19923) [ty] fix lazy snapshot sweeping in nested scopes (#19908)
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Summary
This PR closes astral-sh/ty#955.
Test Plan
New test cases in
narrowing/conditionals/nested.md.