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[pyupgrade] Fix false positive for TypeVar with default on Python <3.13 (UP046,UP047) (#21045)

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## Summary

Type default for Type parameter was added in Python 3.13 (PEP 696).

`typing_extensions.TypeVar` backports the default argument to earlier
versions.

`UP046` & `UP047` were getting triggered when
`typing_extensions.TypeVar` with `default` argument was used on python
version < 3.13

It shouldn't be triggered for python version < 3.13

This commit fixes the bug by adding a python version check before
triggering them.

Fixes #20929.

## Test Plan

### Manual testing 1

As the issue author pointed out in
https://github.com/astral-sh/ruff/issues/20929#issuecomment-3413194511,
ran the following on `main` branch:
> % cargo run -p ruff -- check ../efax/ --target-version py312
--no-cache

<details><summary>Output</summary>

```zsh
   Compiling ruff_linter v0.14.1 (/Users/prakhar/ruff/crates/ruff_linter)
   Compiling ruff v0.14.1 (/Users/prakhar/ruff/crates/ruff)
   Compiling ruff_graph v0.1.0 (/Users/prakhar/ruff/crates/ruff_graph)
   Compiling ruff_workspace v0.0.0 (/Users/prakhar/ruff/crates/ruff_workspace)
   Compiling ruff_server v0.2.2 (/Users/prakhar/ruff/crates/ruff_server)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 6.72s
     Running `target/debug/ruff check ../efax/ --target-version py312 --no-cache`
UP046 Generic class `ExpectationParametrization` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/expectation_parametrization.py:17:48
   |
17 | class ExpectationParametrization(Distribution, Generic[NP]):
   |                                                ^^^^^^^^^^^
18 |     """The expectation parametrization of an exponential family distribution.
   |
help: Use type parameters

UP046 Generic class `ExpToNat` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/mixins/exp_to_nat/exp_to_nat.py:27:68
   |
26 | @dataclass
27 | class ExpToNat(ExpectationParametrization[NP], SimpleDistribution, Generic[NP]):
   |                                                                    ^^^^^^^^^^^
28 |     """This mixin implements the conversion from expectation to natural parameters.
   |
help: Use type parameters

UP046 Generic class `HasEntropyEP` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/mixins/has_entropy.py:25:20
   |
23 |                    HasEntropy,
24 |                    JaxAbstractClass,
25 |                    Generic[NP]):
   |                    ^^^^^^^^^^^
26 |     @abstract_jit
27 |     @abstractmethod
   |
help: Use type parameters

UP046 Generic class `HasEntropyNP` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/mixins/has_entropy.py:64:20
   |
62 | class HasEntropyNP(NaturalParametrization[EP],
63 |                    HasEntropy,
64 |                    Generic[EP]):
   |                    ^^^^^^^^^^^
65 |     @jit
66 |     @final
   |
help: Use type parameters

UP046 Generic class `NaturalParametrization` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/natural_parametrization.py:43:30
   |
41 | class NaturalParametrization(Distribution,
42 |                              JaxAbstractClass,
43 |                              Generic[EP, Domain]):
   |                              ^^^^^^^^^^^^^^^^^^^
44 |     """The natural parametrization of an exponential family distribution.
   |
help: Use type parameters

UP046 Generic class `Structure` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/structure/structure.py:31:17
   |
30 | @dataclass
31 | class Structure(Generic[P]):
   |                 ^^^^^^^^^^
32 |     """This class generalizes the notion of type for Distribution objects.
   |
help: Use type parameters

UP046 Generic class `DistributionInfo` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/tests/distribution_info.py:20:24
   |
20 | class DistributionInfo(Generic[NP, EP, Domain]):
   |                        ^^^^^^^^^^^^^^^^^^^^^^^
21 |     def __init__(self, dimensions: int = 1, safety: float = 0.0) -> None:
22 |         super().__init__()
   |
help: Use type parameters

Found 7 errors.
No fixes available (7 hidden fixes can be enabled with the `--unsafe-fixes` option).
```
</details> 

Running it after the changes:
```zsh
ruff % cargo run -p ruff -- check ../efax/ --target-version py312 --no-cache
   Compiling ruff_linter v0.14.1 (/Users/prakhar/ruff/crates/ruff_linter)
   Compiling ruff v0.14.1 (/Users/prakhar/ruff/crates/ruff)
   Compiling ruff_graph v0.1.0 (/Users/prakhar/ruff/crates/ruff_graph)
   Compiling ruff_workspace v0.0.0 (/Users/prakhar/ruff/crates/ruff_workspace)
   Compiling ruff_server v0.2.2 (/Users/prakhar/ruff/crates/ruff_server)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 7.86s
     Running `target/debug/ruff check ../efax/ --target-version py312 --no-cache`
All checks passed!
```

---

### Manual testing 2

Ran the check on the following script (mainly to verify `UP047`):
```py
from __future__ import annotations                                                                                                                                                    

from typing import Generic

from typing_extensions import TypeVar

T = TypeVar("T", default=int)


def generic_function(var: T) -> T:
    return var


Q = TypeVar("Q", default=str)


class GenericClass(Generic[Q]):
    var: Q
```

On `main` branch:
> ruff % cargo run -p ruff -- check ~/up046.py --target-version py312
--preview --no-cache

<details><summary>Output</summary>

```zsh
   Compiling ruff_linter v0.14.1 (/Users/prakhar/ruff/crates/ruff_linter)
   Compiling ruff v0.14.1 (/Users/prakhar/ruff/crates/ruff)
   Compiling ruff_graph v0.1.0 (/Users/prakhar/ruff/crates/ruff_graph)
   Compiling ruff_workspace v0.0.0 (/Users/prakhar/ruff/crates/ruff_workspace)
   Compiling ruff_server v0.2.2 (/Users/prakhar/ruff/crates/ruff_server)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 7.43s
     Running `target/debug/ruff check /Users/prakhar/up046.py --target-version py312 --preview --no-cache`
UP047 Generic function `generic_function` should use type parameters
  --> /Users/prakhar/up046.py:10:5
   |
10 | def generic_function(var: T) -> T:
   |     ^^^^^^^^^^^^^^^^^^^^^^^^
11 |     return var
   |
help: Use type parameters

UP046 Generic class `GenericClass` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/up046.py:17:20
   |
17 | class GenericClass(Generic[Q]):
   |                    ^^^^^^^^^^
18 |     var: Q
   |
help: Use type parameters

Found 2 errors.
No fixes available (2 hidden fixes can be enabled with the `--unsafe-fixes` option).
```

</details> 

After the fix (this branch):
```zsh
ruff % cargo run -p ruff -- check ~/up046.py --target-version py312 --preview --no-cache
   Compiling ruff_linter v0.14.1 (/Users/prakhar/ruff/crates/ruff_linter)
   Compiling ruff v0.14.1 (/Users/prakhar/ruff/crates/ruff)
   Compiling ruff_graph v0.1.0 (/Users/prakhar/ruff/crates/ruff_graph)
   Compiling ruff_workspace v0.0.0 (/Users/prakhar/ruff/crates/ruff_workspace)
   Compiling ruff_server v0.2.2 (/Users/prakhar/ruff/crates/ruff_server)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 7.40s
     Running `target/debug/ruff check /Users/prakhar/up046.py --target-version py312 --preview --no-cache`
All checks passed!
```

Signed-off-by: Prakhar Pratyush <prakhar1144@gmail.com>
This commit is contained in:
Prakhar Pratyush 2025-10-30 22:29:07 +05:30 • committed by GitHub
parent e55bc943e5
commit 10bda3df00
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
9 changed files with 67 additions and 14 deletions
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13
crates/ruff_linter/resources/test/fixtures/pyupgrade/UP046_2.py vendored Normal file
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@ -0,0 +1,13 @@
"""This is placed in a separate fixture as `TypeVar` needs to be imported
from `typing_extensions` to support default arguments in Python version < 3.13.
We verify that UP046 doesn't apply in this case.
"""
from typing import Generic
from typing_extensions import TypeVar
T = TypeVar("T", default=str)
class DefaultTypeVar(Generic[T]):
var: T

0
crates/ruff_linter/resources/test/fixtures/pyupgrade/UP047.py → crates/ruff_linter/resources/test/fixtures/pyupgrade/UP047_0.py vendored
View file

12
crates/ruff_linter/resources/test/fixtures/pyupgrade/UP047_1.py vendored Normal file
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@ -0,0 +1,12 @@
"""This is placed in a separate fixture as `TypeVar` needs to be imported
from `typing_extensions` to support default arguments in Python version < 3.13.
We verify that UP047 doesn't apply in this case.
"""
from typing_extensions import TypeVar
T = TypeVar("T", default=int)
def default_var(var: T) -> T:
return var

20
crates/ruff_linter/src/rules/pyupgrade/mod.rs
View file

@ -111,7 +111,7 @@ mod tests {
#[test_case(Rule::NonPEP695TypeAlias, Path::new("UP040.pyi"))]
#[test_case(Rule::NonPEP695GenericClass, Path::new("UP046_0.py"))]
#[test_case(Rule::NonPEP695GenericClass, Path::new("UP046_1.py"))]
#[test_case(Rule::NonPEP695GenericFunction, Path::new("UP047.py"))]
#[test_case(Rule::NonPEP695GenericFunction, Path::new("UP047_0.py"))]
#[test_case(Rule::PrivateTypeParameter, Path::new("UP049_0.py"))]
#[test_case(Rule::PrivateTypeParameter, Path::new("UP049_1.py"))]
#[test_case(Rule::UselessClassMetaclassType, Path::new("UP050.py"))]
@ -125,6 +125,22 @@ mod tests {
Ok(())
}
#[test_case(Rule::NonPEP695GenericClass, Path::new("UP046_2.py"))]
#[test_case(Rule::NonPEP695GenericFunction, Path::new("UP047_1.py"))]
fn rules_not_applied_default_typevar_backported(rule_code: Rule, path: &Path) -> Result<()> {
let snapshot = path.to_string_lossy().to_string();
let diagnostics = test_path(
Path::new("pyupgrade").join(path).as_path(),
&settings::LinterSettings {
preview: PreviewMode::Enabled,
unresolved_target_version: PythonVersion::PY312.into(),
..settings::LinterSettings::for_rule(rule_code)
},
)?;
assert_diagnostics!(snapshot, diagnostics);
Ok(())
}
#[test_case(Rule::SuperCallWithParameters, Path::new("UP008.py"))]
#[test_case(Rule::TypingTextStrAlias, Path::new("UP019.py"))]
fn rules_preview(rule_code: Rule, path: &Path) -> Result<()> {
@ -144,7 +160,7 @@ mod tests {
#[test_case(Rule::NonPEP695TypeAlias, Path::new("UP040.pyi"))]
#[test_case(Rule::NonPEP695GenericClass, Path::new("UP046_0.py"))]
#[test_case(Rule::NonPEP695GenericClass, Path::new("UP046_1.py"))]
#[test_case(Rule::NonPEP695GenericFunction, Path::new("UP047.py"))]
#[test_case(Rule::NonPEP695GenericFunction, Path::new("UP047_0.py"))]
fn type_var_default_preview(rule_code: Rule, path: &Path) -> Result<()> {
let snapshot = format!("{}__preview_diff", path.to_string_lossy());
assert_diagnostics_diff!(

14
crates/ruff_linter/src/rules/pyupgrade/rules/pep695/mod.rs
View file

@ -6,8 +6,8 @@ use std::fmt::Display;
use itertools::Itertools;
use ruff_python_ast::{
self as ast, Arguments, Expr, ExprCall, ExprName, ExprSubscript, Identifier, Stmt, StmtAssign,
TypeParam, TypeParamParamSpec, TypeParamTypeVar, TypeParamTypeVarTuple,
self as ast, Arguments, Expr, ExprCall, ExprName, ExprSubscript, Identifier, PythonVersion,
Stmt, StmtAssign, TypeParam, TypeParamParamSpec, TypeParamTypeVar, TypeParamTypeVarTuple,
name::Name,
visitor::{self, Visitor},
};
@ -369,15 +369,19 @@ fn in_nested_context(checker: &Checker) -> bool {
}
/// Deduplicate `vars`, returning `None` if `vars` is empty or any duplicates are found.
/// Also returns `None` if any `TypeVar` has a default value and preview mode is not enabled.
/// Also returns `None` if any `TypeVar` has a default value and the target Python version
/// is below 3.13 or preview mode is not enabled. Note that `typing_extensions` backports
/// the default argument, but the rule should be skipped in that case.
fn check_type_vars<'a>(vars: Vec<TypeVar<'a>>, checker: &Checker) -> Option<Vec<TypeVar<'a>>> {
if vars.is_empty() {
return None;
}
// If any type variables have defaults and preview mode is not enabled, skip the rule
// If any type variables have defaults, skip the rule unless
// running with preview mode enabled and targeting Python 3.13+.
if vars.iter().any(|tv| tv.default.is_some())
&& !is_type_var_default_enabled(checker.settings())
&& (checker.target_version() < PythonVersion::PY313
|| !is_type_var_default_enabled(checker.settings()))
{
return None;
}

4
crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP046_2.py.snap Normal file
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@ -0,0 +1,4 @@
---
source: crates/ruff_linter/src/rules/pyupgrade/mod.rs
---

12
crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP047.py.snap → crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP047_0.py.snap
View file

@ -2,7 +2,7 @@
source: crates/ruff_linter/src/rules/pyupgrade/mod.rs
---
UP047 [*] Generic function `f` should use type parameters
--> UP047.py:12:5
--> UP047_0.py:12:5
|
12 | def f(t: T) -> T:
| ^^^^^^^
@ -20,7 +20,7 @@ help: Use type parameters
note: This is an unsafe fix and may change runtime behavior
UP047 [*] Generic function `g` should use type parameters
--> UP047.py:16:5
--> UP047_0.py:16:5
|
16 | def g(ts: tuple[*Ts]) -> tuple[*Ts]:
| ^^^^^^^^^^^^^^^^^
@ -38,7 +38,7 @@ help: Use type parameters
note: This is an unsafe fix and may change runtime behavior
UP047 [*] Generic function `h` should use type parameters
--> UP047.py:20:5
--> UP047_0.py:20:5
|
20 | def h(
| _____^
@ -62,7 +62,7 @@ help: Use type parameters
note: This is an unsafe fix and may change runtime behavior
UP047 [*] Generic function `i` should use type parameters
--> UP047.py:29:5
--> UP047_0.py:29:5
|
29 | def i(s: S) -> S:
| ^^^^^^^
@ -80,7 +80,7 @@ help: Use type parameters
note: This is an unsafe fix and may change runtime behavior
UP047 [*] Generic function `broken_fix` should use type parameters
--> UP047.py:39:5
--> UP047_0.py:39:5
|
37 | # TypeVars with the new-style generic syntax and will be rejected by type
38 | # checkers
@ -100,7 +100,7 @@ help: Use type parameters
note: This is an unsafe fix and may change runtime behavior
UP047 [*] Generic function `any_str_param` should use type parameters
--> UP047.py:43:5
--> UP047_0.py:43:5
|
43 | def any_str_param(s: AnyStr) -> AnyStr:
| ^^^^^^^^^^^^^^^^^^^^^^^^

2
crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP047.py__preview_diff.snap → crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP047_0.py__preview_diff.snap
View file

@ -11,7 +11,7 @@ Added: 1
--- Added ---
UP047 [*] Generic function `default_var` should use type parameters
--> UP047.py:51:5
--> UP047_0.py:51:5
|
51 | def default_var(v: V) -> V:
| ^^^^^^^^^^^^^^^^^

4
crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP047_1.py.snap Normal file
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@ -0,0 +1,4 @@
---
source: crates/ruff_linter/src/rules/pyupgrade/mod.rs
---