[pyflakes] Treat arguments passed to the default= parameter of `T…

…ypeVar` as type expressions (`F821`) (#15679)

crates/ruff_linter/resources/test/fixtures/pyflakes/F821_32.pyi

@@ -0,0 +1,6 @@
+from typing import TypeVar
+
+# Forward references are okay for both `bound` and `default` in a stub file
+_P = TypeVar("_P", bound=X, default=X)
+
+class X: ...

crates/ruff_linter/src/checkers/ast/mod.rs

@@ -1326,7 +1326,7 @@ impl<'a> Visitor<'a> for Checker<'a> {
                                 range: _,
                             } = keyword;
                             if let Some(id) = arg {
-                                if id.as_str() == "bound" {
+                                if matches!(&**id, "bound" | "default") {
                                     self.visit_type_definition(value);
                                 } else {
                                     self.visit_non_type_definition(value);

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

@@ -164,6 +164,7 @@ mod tests {
     #[test_case(Rule::UndefinedName, Path::new("F821_28.py"))]
     #[test_case(Rule::UndefinedName, Path::new("F821_30.py"))]
     #[test_case(Rule::UndefinedName, Path::new("F821_31.py"))]
+    #[test_case(Rule::UndefinedName, Path::new("F821_32.pyi"))]
     #[test_case(Rule::UndefinedExport, Path::new("F822_0.py"))]
     #[test_case(Rule::UndefinedExport, Path::new("F822_0.pyi"))]
     #[test_case(Rule::UndefinedExport, Path::new("F822_1.py"))]

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F821_F821_32.pyi.snap

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