[pyupgrade] Enable rule triggering for stub files (UP043) (#20027)

## Summary
Resolves #20011

Implemented alternative triggering condition for rule
[`UP043`](https://docs.astral.sh/ruff/rules/unnecessary-default-type-args/)
based on requirements outlined in [issue
#20011](https://github.com/astral-sh/ruff/issues/20011)
## Test Plan
Created .pyi file to ensure triggering the rule

---------

Co-authored-by: Igor Drokin <drokinii1017@gmail.com>
Co-authored-by: dylwil3 <dylwil3@gmail.com>

crates/ruff_linter/resources/test/fixtures/pyupgrade/UP043.pyi

@@ -0,0 +1,59 @@
+from collections.abc import Generator, AsyncGenerator
+
+
+def func() -> Generator[int, None, None]:
+    yield 42
+
+
+def func() -> Generator[int, None]:
+    yield 42
+
+
+def func() -> Generator[int]:
+    yield 42
+
+
+def func() -> Generator[int, int, int]:
+    foo = yield 42
+    return foo
+
+
+def func() -> Generator[int, int, None]:
+    _ = yield 42
+    return None
+
+
+def func() -> Generator[int, None, int]:
+    yield 42
+    return 42
+
+
+async def func() -> AsyncGenerator[int, None]:
+    yield 42
+
+
+async def func() -> AsyncGenerator[int]:
+    yield 42
+
+
+async def func() -> AsyncGenerator[int, int]:
+    foo = yield 42
+    return foo
+
+
+from typing import Generator, AsyncGenerator
+
+
+def func() -> Generator[str, None, None]:
+    yield "hello"
+
+
+async def func() -> AsyncGenerator[str, None]:
+    yield "hello"
+
+
+async def func() -> AsyncGenerator[  # type: ignore
+    str,
+    None
+]:
+    yield "hello"

crates/ruff_linter/src/checkers/ast/analyze/expression.rs

@@ -9,6 +9,7 @@ use ruff_text_size::Ranged;
 use crate::checkers::ast::Checker;
 use crate::preview::{
     is_assert_raises_exception_call_enabled, is_optional_as_none_in_union_enabled,
+    is_unnecessary_default_type_args_stubs_enabled,
 };
 use crate::registry::Rule;
 use crate::rules::{
@@ -142,7 +143,10 @@ pub(crate) fn expression(expr: &Expr, checker: &Checker) {
             }
 
             if checker.is_rule_enabled(Rule::UnnecessaryDefaultTypeArgs) {
-                if checker.target_version() >= PythonVersion::PY313 {
+                if checker.target_version() >= PythonVersion::PY313
+                    || is_unnecessary_default_type_args_stubs_enabled(checker.settings())
+                        && checker.semantic().in_stub_file()
+                {
                     pyupgrade::rules::unnecessary_default_type_args(checker, expr);
                 }
             }

crates/ruff_linter/src/preview.rs

@@ -260,3 +260,10 @@ pub(crate) const fn is_maxsplit_without_separator_fix_enabled(settings: &LinterS
 pub(crate) const fn is_bidi_forbid_arabic_letter_mark_enabled(settings: &LinterSettings) -> bool {
     settings.preview.is_enabled()
 }
+
+// https://github.com/astral-sh/ruff/pull/20027
+pub(crate) const fn is_unnecessary_default_type_args_stubs_enabled(
+    settings: &LinterSettings,
+) -> bool {
+    settings.preview.is_enabled()
+}

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

@@ -357,4 +357,19 @@ mod tests {
         2 | from pipes import quote, Template
         ");
     }
+
+    #[test]
+    fn unnecessary_default_type_args_stubs_py312_preview() -> Result<()> {
+        let snapshot = format!("{}__preview", "UP043.pyi");
+        let diagnostics = test_path(
+            Path::new("pyupgrade/UP043.pyi"),
+            &settings::LinterSettings {
+                preview: PreviewMode::Enabled,
+                unresolved_target_version: PythonVersion::PY312.into(),
+                ..settings::LinterSettings::for_rule(Rule::UnnecessaryDefaultTypeArgs)
+            },
+        )?;
+        assert_diagnostics!(snapshot, diagnostics);
+        Ok(())
+    }
 }

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

@@ -8,6 +8,7 @@ use crate::{AlwaysFixableViolation, Applicability, Edit, Fix};
 /// ## What it does
 /// Checks for unnecessary default type arguments for `Generator` and
 /// `AsyncGenerator` on Python 3.13+.
+/// In [preview], this rule will also apply to stub files.
 ///
 /// ## Why is this bad?
 /// Python 3.13 introduced the ability for type parameters to specify default
@@ -59,6 +60,8 @@ use crate::{AlwaysFixableViolation, Applicability, Edit, Fix};
 /// - [Annotating generators and coroutines](https://docs.python.org/3/library/typing.html#annotating-generators-and-coroutines)
 /// - [Python documentation: `typing.Generator`](https://docs.python.org/3/library/typing.html#typing.Generator)
 /// - [Python documentation: `typing.AsyncGenerator`](https://docs.python.org/3/library/typing.html#typing.AsyncGenerator)
+///
+/// [preview]: https://docs.astral.sh/ruff/preview/
 #[derive(ViolationMetadata)]
 pub(crate) struct UnnecessaryDefaultTypeArgs;
 

crates/ruff_linter/src/rules/pyupgrade/snapshots/ruff_linter__rules__pyupgrade__tests__UP043.pyi__preview.snap

@@ -0,0 +1,128 @@
+---
+source: crates/ruff_linter/src/rules/pyupgrade/mod.rs
+---
+UP043 [*] Unnecessary default type arguments
+ --> UP043.pyi:4:15
+  |
+4 | def func() -> Generator[int, None, None]:
+  |               ^^^^^^^^^^^^^^^^^^^^^^^^^^
+5 |     yield 42
+  |
+help: Remove default type arguments
+1 | from collections.abc import Generator, AsyncGenerator
+2 | 
+3 | 
+  - def func() -> Generator[int, None, None]:
+4 + def func() -> Generator[int]:
+5 |     yield 42
+6 | 
+7 | 
+
+UP043 [*] Unnecessary default type arguments
+ --> UP043.pyi:8:15
+  |
+8 | def func() -> Generator[int, None]:
+  |               ^^^^^^^^^^^^^^^^^^^^
+9 |     yield 42
+  |
+help: Remove default type arguments
+5  |     yield 42
+6  | 
+7  | 
+   - def func() -> Generator[int, None]:
+8  + def func() -> Generator[int]:
+9  |     yield 42
+10 | 
+11 | 
+
+UP043 [*] Unnecessary default type arguments
+  --> UP043.pyi:21:15
+   |
+21 | def func() -> Generator[int, int, None]:
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^
+22 |     _ = yield 42
+23 |     return None
+   |
+help: Remove default type arguments
+18 |     return foo
+19 | 
+20 | 
+   - def func() -> Generator[int, int, None]:
+21 + def func() -> Generator[int, int]:
+22 |     _ = yield 42
+23 |     return None
+24 | 
+
+UP043 [*] Unnecessary default type arguments
+  --> UP043.pyi:31:21
+   |
+31 | async def func() -> AsyncGenerator[int, None]:
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^
+32 |     yield 42
+   |
+help: Remove default type arguments
+28 |     return 42
+29 | 
+30 | 
+   - async def func() -> AsyncGenerator[int, None]:
+31 + async def func() -> AsyncGenerator[int]:
+32 |     yield 42
+33 | 
+34 | 
+
+UP043 [*] Unnecessary default type arguments
+  --> UP043.pyi:47:15
+   |
+47 | def func() -> Generator[str, None, None]:
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^
+48 |     yield "hello"
+   |
+help: Remove default type arguments
+44 | from typing import Generator, AsyncGenerator
+45 | 
+46 | 
+   - def func() -> Generator[str, None, None]:
+47 + def func() -> Generator[str]:
+48 |     yield "hello"
+49 | 
+50 | 
+
+UP043 [*] Unnecessary default type arguments
+  --> UP043.pyi:51:21
+   |
+51 | async def func() -> AsyncGenerator[str, None]:
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^
+52 |     yield "hello"
+   |
+help: Remove default type arguments
+48 |     yield "hello"
+49 | 
+50 | 
+   - async def func() -> AsyncGenerator[str, None]:
+51 + async def func() -> AsyncGenerator[str]:
+52 |     yield "hello"
+53 | 
+54 | 
+
+UP043 [*] Unnecessary default type arguments
+  --> UP043.pyi:55:21
+   |
+55 |   async def func() -> AsyncGenerator[  # type: ignore
+   |  _____________________^
+56 | |     str,
+57 | |     None
+58 | | ]:
+   | |_^
+59 |       yield "hello"
+   |
+help: Remove default type arguments
+52 |     yield "hello"
+53 | 
+54 | 
+   - async def func() -> AsyncGenerator[  # type: ignore
+   -     str,
+   -     None
+   - ]:
+55 + async def func() -> AsyncGenerator[str]:
+56 |     yield "hello"
+note: This is an unsafe fix and may change runtime behavior