Lazily evaluate all PEP 695 type alias values

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_19.py

@@ -0,0 +1,17 @@
+"""Test that type parameters are considered used."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from collections.abc import Callable
+
+    from .foo import Record as Record1
+    from .bar import Record as Record2
+
+type RecordCallback[R: Record1] = Callable[[R], None]
+
+
+def process_record[R: Record2](record: R) -> None:
+    ...

crates/ruff_linter/resources/test/fixtures/pyflakes/F821_20.py

@@ -0,0 +1,5 @@
+"""Test lazy evaluation of type alias values."""
+
+type RecordCallback[R: Record] = Callable[[R], None]
+
+from collections.abc import Callable

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

@@ -1,4 +1,4 @@
-use ruff_python_ast::{Expr, TypeParam};
+use ruff_python_ast::Expr;
 use ruff_python_semantic::{ScopeId, Snapshot};
 use ruff_text_size::TextRange;
 
@@ -10,7 +10,7 @@ pub(crate) struct Deferred<'a> {
     pub(crate) scopes: Vec<ScopeId>,
     pub(crate) string_type_definitions: Vec<(TextRange, &'a str, Snapshot)>,
     pub(crate) future_type_definitions: Vec<(&'a Expr, Snapshot)>,
-    pub(crate) type_param_definitions: Vec<(&'a TypeParam, Snapshot)>,
+    pub(crate) type_param_definitions: Vec<(&'a Expr, Snapshot)>,
     pub(crate) functions: Vec<Snapshot>,
     pub(crate) lambdas: Vec<(&'a Expr, Snapshot)>,
     pub(crate) for_loops: Vec<Snapshot>,

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

@@ -582,9 +582,9 @@ where
                 if let Some(type_params) = type_params {
                     self.visit_type_params(type_params);
                 }
-                // The value in a `type` alias has annotation semantics, in that it's never
-                // evaluated at runtime.
-                self.visit_annotation(value);
+                self.deferred
+                    .type_param_definitions
+                    .push((value, self.semantic.snapshot()));
                 self.semantic.pop_scope();
                 self.visit_expr(name);
             }
@@ -1389,9 +1389,14 @@ where
             }
         }
         // Step 2: Traversal
-        self.deferred
-            .type_param_definitions
-            .push((type_param, self.semantic.snapshot()));
+        if let ast::TypeParam::TypeVar(ast::TypeParamTypeVar {
+            bound: Some(bound), ..
+        }) = type_param
+        {
+            self.deferred
+                .type_param_definitions
+                .push((bound, self.semantic.snapshot()));
+        }
     }
 }
 
@@ -1766,12 +1771,9 @@ impl<'a> Checker<'a> {
             for (type_param, snapshot) in type_params {
                 self.semantic.restore(snapshot);
 
-                if let ast::TypeParam::TypeVar(ast::TypeParamTypeVar {
-                    bound: Some(bound), ..
-                }) = type_param
-                {
-                    self.visit_annotation(bound);
-                }
+                self.semantic.flags |=
+                    SemanticModelFlags::TYPE_PARAM_DEFINITION | SemanticModelFlags::TYPE_DEFINITION;
+                self.visit_expr(type_param);
             }
         }
         self.semantic.restore(snapshot);

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

@@ -50,6 +50,7 @@ mod tests {
     #[test_case(Rule::UnusedImport, Path::new("F401_16.py"))]
     #[test_case(Rule::UnusedImport, Path::new("F401_17.py"))]
     #[test_case(Rule::UnusedImport, Path::new("F401_18.py"))]
+    #[test_case(Rule::UnusedImport, Path::new("F401_19.py"))]
     #[test_case(Rule::ImportShadowedByLoopVar, Path::new("F402.py"))]
     #[test_case(Rule::UndefinedLocalWithImportStar, Path::new("F403.py"))]
     #[test_case(Rule::LateFutureImport, Path::new("F404.py"))]
@@ -135,6 +136,7 @@ mod tests {
     #[test_case(Rule::UndefinedName, Path::new("F821_17.py"))]
     #[test_case(Rule::UndefinedName, Path::new("F821_18.py"))]
     #[test_case(Rule::UndefinedName, Path::new("F821_19.py"))]
+    #[test_case(Rule::UndefinedName, Path::new("F821_20.py"))]
     #[test_case(Rule::UndefinedExport, Path::new("F822_0.py"))]
     #[test_case(Rule::UndefinedExport, Path::new("F822_1.py"))]
     #[test_case(Rule::UndefinedExport, Path::new("F822_2.py"))]

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F401_F401_19.py.snap

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

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F821_F821_20.py.snap

@@ -0,0 +1,14 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+F821_20.py:3:24: F821 Undefined name `Record`
+  |
+1 | """Test lazy evaluation of type alias values."""
+2 | 
+3 | type RecordCallback[R: Record] = Callable[[R], None]
+  |                        ^^^^^^ F821
+4 | 
+5 | from collections.abc import Callable
+  |
+
+

crates/ruff_python_semantic/src/model.rs

@@ -1600,6 +1600,16 @@ bitflags! {
         /// ```
         const FUTURE_ANNOTATIONS = 1 << 14;
 
+        /// The model is in a type parameter definition.
+        ///
+        /// For example, the model could be visiting `Record` in:
+        /// ```python
+        /// from typing import TypeVar
+        ///
+        /// Record = TypeVar("Record")
+        ///
+        const TYPE_PARAM_DEFINITION = 1 << 15;
+
         /// The context is in any type annotation.
         const ANNOTATION = Self::TYPING_ONLY_ANNOTATION.bits() | Self::RUNTIME_ANNOTATION.bits();
 
@@ -1610,11 +1620,12 @@ bitflags! {
         /// The context is in any deferred type definition.
         const DEFERRED_TYPE_DEFINITION = Self::SIMPLE_STRING_TYPE_DEFINITION.bits()
             | Self::COMPLEX_STRING_TYPE_DEFINITION.bits()
-            | Self::FUTURE_TYPE_DEFINITION.bits();
+            | Self::FUTURE_TYPE_DEFINITION.bits()
+            | Self::TYPE_PARAM_DEFINITION.bits();
 
         /// The context is in a typing-only context.
         const TYPING_CONTEXT = Self::TYPE_CHECKING_BLOCK.bits() | Self::TYPING_ONLY_ANNOTATION.bits() |
-            Self::STRING_TYPE_DEFINITION.bits();
+            Self::STRING_TYPE_DEFINITION.bits() | Self::TYPE_PARAM_DEFINITION.bits();
     }
 }