Add a test case

crates/ruff_linter/resources/test/fixtures/pyflakes/F821_29.py

@@ -0,0 +1,23 @@
+"""Regression test for #10451.
+
+Annotations in a class are allowed to be forward references
+if `from __future__ import annotations` is active,
+even if they're in a class included in
+`lint.flake8-type-checking.runtime-evaluated-base-classes`.
+
+They're not allowed to refer to symbols that cannot be *resolved*
+at runtime, however.
+"""
+
+from __future__ import annotations
+
+from sqlalchemy.orm import DeclarativeBase, Mapped
+
+
+class Base(DeclarativeBase):
+    some_mapping: Mapped[list[Bar]] | None = None  # Should not trigger F821 (resolveable forward reference)
+    simplified: list[Bar] | None = None  # Should not trigger F821 (resolveable forward reference)
+
+
+class Bar:
+    pass

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

@@ -180,6 +180,29 @@ mod tests {
         Ok(())
     }
 
+    #[test_case(Rule::UndefinedName, Path::new("F821_29.py"))]
+    fn rules_with_flake8_type_checking_settings_enabled(
+        rule_code: Rule,
+        path: &Path,
+    ) -> Result<()> {
+        let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());
+        let diagnostics = test_path(
+            Path::new("pyflakes").join(path).as_path(),
+            &LinterSettings {
+                flake8_type_checking: crate::rules::flake8_type_checking::settings::Settings {
+                    runtime_required_base_classes: vec![
+                        "pydantic.BaseModel".to_string(),
+                        "sqlalchemy.orm.DeclarativeBase".to_string(),
+                    ],
+                    ..Default::default()
+                },
+                ..LinterSettings::for_rule(rule_code)
+            },
+        )?;
+        assert_messages!(snapshot, diagnostics);
+        Ok(())
+    }
+
     #[test_case(Rule::UnusedVariable, Path::new("F841_4.py"))]
     fn preview_rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!(

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F821_F821_29.py.snap

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

repro.py

@@ -0,0 +1,18 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from sqlalchemy.orm import DeclarativeBase, Mapped
+
+if TYPE_CHECKING:
+    from whatever import whatever
+
+
+class Base(DeclarativeBase):
+    some_mapping: Mapped[list[Bar]] | None = None # F821 Undefined name `Bar`
+    simplified: list[Bar] | None = None # F821 Undefined name `Bar`
+    bad: whatever
+
+
+class Bar:
+    pass