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

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP046_2.py

@@ -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

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP047_1.py

@@ -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

crates/ruff_linter/src/rules/pyupgrade/mod.rs

@@ -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!(

crates/ruff_linter/src/rules/pyupgrade/rules/pep695/mod.rs

@@ -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;
     }

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP046_2.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff_linter/src/rules/pyupgrade/mod.rs
+---
+

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

@@ -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:
    |     ^^^^^^^^^^^^^^^^^^^^^^^^

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

@@ -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:
    |     ^^^^^^^^^^^^^^^^^

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP047_1.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff_linter/src/rules/pyupgrade/mod.rs
+---
+