Avoid attributing runtime references to module-level imports (#4942)

crates/ruff/resources/test/fixtures/pyflakes/F401_17.py

@@ -0,0 +1,32 @@
+"""Test that runtime typing references are properly attributed to scoped imports."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, cast
+
+if TYPE_CHECKING:
+    from threading import Thread
+
+
+def fn(thread: Thread):
+    from threading import Thread
+
+    # The `Thread` on the left-hand side should resolve to the `Thread` imported at the
+    # top level.
+    x: Thread
+
+
+def fn(thread: Thread):
+    from threading import Thread
+
+    # The `Thread` on the left-hand side should resolve to the `Thread` imported at the
+    # top level.
+    cast("Thread", thread)
+
+
+def fn(thread: Thread):
+    from threading import Thread
+
+    # The `Thread` on the right-hand side should resolve to the`Thread` imported within
+    # `fn`.
+    cast(Thread, thread)

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

@@ -42,6 +42,7 @@ mod tests {
     #[test_case(Rule::UnusedImport, Path::new("F401_14.py"))]
     #[test_case(Rule::UnusedImport, Path::new("F401_15.py"))]
     #[test_case(Rule::UnusedImport, Path::new("F401_16.py"))]
+    #[test_case(Rule::UnusedImport, Path::new("F401_17.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"))]

crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__F401_F401_17.py.snap

@@ -0,0 +1,42 @@
+---
+source: crates/ruff/src/rules/pyflakes/mod.rs
+---
+F401_17.py:12:27: F401 [*] `threading.Thread` imported but unused
+   |
+12 | def fn(thread: Thread):
+13 |     from threading import Thread
+   |                           ^^^^^^ F401
+14 | 
+15 |     # The `Thread` on the left-hand side should resolve to the `Thread` imported at the
+   |
+   = help: Remove unused import: `threading.Thread`
+
+ℹ Fix
+9  9  | 
+10 10 | 
+11 11 | def fn(thread: Thread):
+12    |-    from threading import Thread
+13 12 | 
+14 13 |     # The `Thread` on the left-hand side should resolve to the `Thread` imported at the
+15 14 |     # top level.
+
+F401_17.py:20:27: F401 [*] `threading.Thread` imported but unused
+   |
+20 | def fn(thread: Thread):
+21 |     from threading import Thread
+   |                           ^^^^^^ F401
+22 | 
+23 |     # The `Thread` on the left-hand side should resolve to the `Thread` imported at the
+   |
+   = help: Remove unused import: `threading.Thread`
+
+ℹ Fix
+17 17 | 
+18 18 | 
+19 19 | def fn(thread: Thread):
+20    |-    from threading import Thread
+21 20 | 
+22 21 |     # The `Thread` on the left-hand side should resolve to the `Thread` imported at the
+23 22 |     # top level.
+
+

crates/ruff_python_semantic/src/model.rs

@@ -178,7 +178,7 @@ impl<'a> SemanticModel<'a> {
     pub fn resolve_reference(&mut self, symbol: &str, range: TextRange) -> ResolvedReference {
         // PEP 563 indicates that if a forward reference can be resolved in the module scope, we
         // should prefer it over local resolutions.
-        if self.in_deferred_type_definition() {
+        if self.in_forward_reference() {
             if let Some(binding_id) = self.scopes.global().get(symbol) {
                 // Mark the binding as used.
                 let context = self.execution_context();
@@ -239,9 +239,7 @@ impl<'a> SemanticModel<'a> {
                 //
                 // The `name` in `print(name)` should be treated as unresolved, but the `name` in
                 // `name: str` should be treated as used.
-                if !self.in_deferred_type_definition()
+                if !self.in_forward_reference() && self.bindings[binding_id].kind.is_annotation() {
-                    && self.bindings[binding_id].kind.is_annotation()
-                {
                     continue;
                 }
 
@@ -756,6 +754,27 @@ impl<'a> SemanticModel<'a> {
             || self.in_future_type_definition()
     }
 
+    /// Return `true` if the context is in a forward type reference.
+    ///
+    /// Includes deferred string types, and future types in annotations.
+    ///
+    /// ## Examples
+    /// ```python
+    /// from __future__ import annotations
+    ///
+    /// from threading import Thread
+    ///
+    ///
+    /// x: Thread  # Forward reference
+    /// cast("Thread", x)  # Forward reference
+    /// cast(Thread, x)  # Non-forward reference
+    /// ```
+    pub const fn in_forward_reference(&self) -> bool {
+        self.in_simple_string_type_definition()
+            || self.in_complex_string_type_definition()
+            || (self.in_future_type_definition() && self.in_annotation())
+    }
+
     /// Return `true` if the context is in an exception handler.
     pub const fn in_exception_handler(&self) -> bool {
         self.flags.contains(SemanticModelFlags::EXCEPTION_HANDLER)