[ty] Completely remove the NoReturn shortcut optimization#23378
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[ty] Completely remove the NoReturn shortcut optimization#23378
NoReturn shortcut optimization#23378Conversation
Typing conformance resultsNo changes detected ✅ |
Memory usage reportSummary
Significant changesClick to expand detailed breakdownflake8
sphinx
trio
prefect
|
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Merging this PR will degrade performance by 4.19%
Performance Changes
Comparing 
Footnotes
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| Lint rule | Added | Removed | Changed |
|---|---|---|---|
call-non-callable |
0 | 2 | 0 |
unresolved-attribute |
2 | 0 | 0 |
invalid-argument-type |
0 | 1 | 0 |
invalid-return-type |
0 | 0 | 1 |
type-assertion-failure |
0 | 1 | 0 |
| Total | 2 | 4 | 1 |
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NoReturn shortcut optimizationNoReturn shortcut optimization
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## Summary
If a generic function's return type depends on a type variable, and the
argument passed resolves that type variable to `Never`, the call should
still be treated as terminal:
```py
def identity[T](x: T) -> T:
return x
def f() -> Never:
identity(exit()) # should be detected as terminal
```
This is a tiny win for correctness, but unfortunately a small drop in
performance and slight increase in memory usage, because we need to
infer more call expressions upfront. If we think it's not important
enough, I'm also okay to change this to a test-only PR that documents
this as a known limitation. If we merge it, I might follow up with an
idea to simplify the code in a [slightly larger refactoring
PR](#23378).
## Memory usage
Insignificant changes on some large internal projects, a 2% *decrease*
in memory usage when running on home-assistant/core.
## Ecosystem
No ecosystem changes, as far as I can tell.
## Test Plan
New Markdown tests
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Author
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The ecosystem hits on mypy are very weird. They have something to do with loop control flow. I can reproduce with this example: from typing import Never
def _(x: str | None):
while True:
def fail() -> Never:
raise
if x is None:
fail()
reveal_type(x) # should be `str`, returns `str | None` on this branch
fail()I think it has something to do with loop-header bindings for |
knutwannheden
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## Summary
If a generic function's return type depends on a type variable, and the
argument passed resolves that type variable to `Never`, the call should
still be treated as terminal:
```py
def identity[T](x: T) -> T:
return x
def f() -> Never:
identity(exit()) # should be detected as terminal
```
This is a tiny win for correctness, but unfortunately a small drop in
performance and slight increase in memory usage, because we need to
infer more call expressions upfront. If we think it's not important
enough, I'm also okay to change this to a test-only PR that documents
this as a known limitation. If we merge it, I might follow up with an
idea to simplify the code in a [slightly larger refactoring
PR](astral-sh#23378).
## Memory usage
Insignificant changes on some large internal projects, a 2% *decrease*
in memory usage when running on home-assistant/core.
## Ecosystem
No ecosystem changes, as far as I can tell.
## Test Plan
New Markdown tests
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Averaging over all benchmarks shows that this looks more like a win in terms of performance 
|
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Summary
Test Plan