Recursively visit deferred AST nodes

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_21.py

@@ -1,3 +1,5 @@
+"""Test: ensure that we visit type definitions and lambdas recursively."""
+
 from __future__ import annotations
 
 from collections import Counter

crates/ruff_linter/resources/test/fixtures/pyflakes/F401_22.py

@@ -0,0 +1,11 @@
+"""Test: ensure that we visit type definitions and lambdas recursively."""
+
+from __future__ import annotations
+
+import re
+import os
+from typing import cast
+
+cast(lambda: re.match, 1)
+
+cast(lambda: cast(lambda: os.path, 1), 1)

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

@@ -6,8 +6,8 @@ use crate::rules::{flake8_bugbear, flake8_simplify, perflint, pyupgrade, refurb}
 
 /// Run lint rules over all deferred for-loops in the [`SemanticModel`].
 pub(crate) fn deferred_for_loops(checker: &mut Checker) {
-    while !checker.deferred.for_loops.is_empty() {
-        let for_loops = std::mem::take(&mut checker.deferred.for_loops);
+    while !checker.analyze.for_loops.is_empty() {
+        let for_loops = std::mem::take(&mut checker.analyze.for_loops);
         for snapshot in for_loops {
             checker.semantic.restore(snapshot);
 

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

@@ -6,8 +6,8 @@ use crate::rules::{flake8_pie, pylint, refurb};
 
 /// Run lint rules over all deferred lambdas in the [`SemanticModel`].
 pub(crate) fn deferred_lambdas(checker: &mut Checker) {
-    while !checker.deferred.lambdas.is_empty() {
-        let lambdas = std::mem::take(&mut checker.deferred.lambdas);
+    while !checker.analyze.lambdas.is_empty() {
+        let lambdas = std::mem::take(&mut checker.analyze.lambdas);
         for snapshot in lambdas {
             checker.semantic.restore(snapshot);
 

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

@@ -77,7 +77,7 @@ pub(crate) fn deferred_scopes(checker: &mut Checker) {
     };
 
     let mut diagnostics: Vec<Diagnostic> = vec![];
-    for scope_id in checker.deferred.scopes.iter().rev().copied() {
+    for scope_id in checker.analyze.scopes.iter().rev().copied() {
         let scope = &checker.semantic.scopes[scope_id];
 
         if checker.enabled(Rule::UndefinedLocal) {

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

@@ -1264,7 +1264,7 @@ pub(crate) fn statement(stmt: &Stmt, checker: &mut Checker) {
                 Rule::UnusedLoopControlVariable,
                 Rule::YieldInForLoop,
             ]) {
-                checker.deferred.for_loops.push(checker.semantic.snapshot());
+                checker.analyze.for_loops.push(checker.semantic.snapshot());
             }
             if checker.enabled(Rule::LoopVariableOverridesIterator) {
                 flake8_bugbear::rules::loop_variable_overrides_iterator(checker, target, iter);

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

@@ -2,16 +2,34 @@ use ruff_python_ast::Expr;
 use ruff_python_semantic::{ScopeId, Snapshot};
 use ruff_text_size::TextRange;
 
-/// A collection of AST nodes that are deferred for later analysis.
-/// Used to, e.g., store functions, whose bodies shouldn't be analyzed until all
-/// module-level definitions have been analyzed.
+/// A collection of AST nodes that are deferred for later visitation. Used to, e.g., store
+/// functions, whose bodies shouldn't be visited until all module-level definitions have been
+/// visited.
 #[derive(Debug, Default)]
-pub(crate) struct Deferred<'a> {
-    pub(crate) scopes: Vec<ScopeId>,
+pub(crate) struct Visit<'a> {
     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 Expr, Snapshot)>,
     pub(crate) functions: Vec<Snapshot>,
     pub(crate) lambdas: Vec<Snapshot>,
+}
+
+impl Visit<'_> {
+    /// Returns `true` if there are no deferred nodes.
+    pub(crate) fn is_empty(&self) -> bool {
+        self.string_type_definitions.is_empty()
+            && self.future_type_definitions.is_empty()
+            && self.type_param_definitions.is_empty()
+            && self.functions.is_empty()
+            && self.lambdas.is_empty()
+    }
+}
+
+/// A collection of AST nodes to be analyzed after the AST traversal. Used to, e.g., store
+/// all `for` loops, so that they can be analyzed after the entire AST has been visited.
+#[derive(Debug, Default)]
+pub(crate) struct Analyze {
+    pub(crate) scopes: Vec<ScopeId>,
+    pub(crate) lambdas: Vec<Snapshot>,
     pub(crate) for_loops: Vec<Snapshot>,
 }

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

@@ -52,14 +52,13 @@ use ruff_python_parser::typing::{parse_type_annotation, AnnotationKind};
 use ruff_python_semantic::analyze::{imports, typing, visibility};
 use ruff_python_semantic::{
     BindingFlags, BindingId, BindingKind, Exceptions, Export, FromImport, Globals, Import, Module,
-    ModuleKind, NodeId, ScopeId, ScopeKind, SemanticModel, SemanticModelFlags, Snapshot,
-    StarImport, SubmoduleImport,
+    ModuleKind, NodeId, ScopeId, ScopeKind, SemanticModel, SemanticModelFlags, StarImport,
+    SubmoduleImport,
 };
 use ruff_python_stdlib::builtins::{IPYTHON_BUILTINS, MAGIC_GLOBALS, PYTHON_BUILTINS};
 use ruff_source_file::{Locator, OneIndexed, SourceRow};
 
 use crate::checkers::ast::annotation::AnnotationContext;
-use crate::checkers::ast::deferred::Deferred;
 use crate::docstrings::extraction::ExtractionTarget;
 use crate::importer::Importer;
 use crate::noqa::NoqaMapping;
@@ -105,8 +104,10 @@ pub(crate) struct Checker<'a> {
     importer: Importer<'a>,
     /// The [`SemanticModel`], built up over the course of the AST traversal.
     semantic: SemanticModel<'a>,
-    /// A set of deferred nodes to be processed after the current traversal (e.g., function bodies).
-    deferred: Deferred<'a>,
+    /// A set of deferred nodes to be visited after the current traversal (e.g., function bodies).
+    visit: deferred::Visit<'a>,
+    /// A set of deferred nodes to be analyzed after the AST traversal (e.g., `for` loops).
+    analyze: deferred::Analyze,
     /// The cumulative set of diagnostics computed across all lint rules.
     pub(crate) diagnostics: Vec<Diagnostic>,
     /// The list of names already seen by flake8-bugbear diagnostics, to avoid duplicate violations..
@@ -145,7 +146,8 @@ impl<'a> Checker<'a> {
             indexer,
             importer,
             semantic: SemanticModel::new(&settings.typing_modules, path, module),
-            deferred: Deferred::default(),
+            visit: deferred::Visit::default(),
+            analyze: deferred::Analyze::default(),
             diagnostics: Vec::default(),
             flake8_bugbear_seen: Vec::default(),
             cell_offsets,
@@ -596,7 +598,7 @@ where
                 self.semantic.push_scope(ScopeKind::Function(function_def));
                 self.semantic.flags -= SemanticModelFlags::EXCEPTION_HANDLER;
 
-                self.deferred.functions.push(self.semantic.snapshot());
+                self.visit.functions.push(self.semantic.snapshot());
 
                 // Extract any global bindings from the function body.
                 if let Some(globals) = Globals::from_body(body) {
@@ -652,7 +654,7 @@ where
                 if let Some(type_params) = type_params {
                     self.visit_type_params(type_params);
                 }
-                self.deferred
+                self.visit
                     .type_param_definitions
                     .push((value, self.semantic.snapshot()));
                 self.semantic.pop_scope();
@@ -785,7 +787,7 @@ where
         match stmt {
             Stmt::FunctionDef(ast::StmtFunctionDef { name, .. }) => {
                 let scope_id = self.semantic.scope_id;
-                self.deferred.scopes.push(scope_id);
+                self.analyze.scopes.push(scope_id);
                 self.semantic.pop_scope(); // Function scope
                 self.semantic.pop_definition();
                 self.semantic.pop_scope(); // Type parameter scope
@@ -798,7 +800,7 @@ where
             }
             Stmt::ClassDef(ast::StmtClassDef { name, .. }) => {
                 let scope_id = self.semantic.scope_id;
-                self.deferred.scopes.push(scope_id);
+                self.analyze.scopes.push(scope_id);
                 self.semantic.pop_scope(); // Class scope
                 self.semantic.pop_definition();
                 self.semantic.pop_scope(); // Type parameter scope
@@ -835,13 +837,13 @@ where
             && self.semantic.future_annotations()
         {
             if let Expr::StringLiteral(ast::ExprStringLiteral { value, .. }) = expr {
-                self.deferred.string_type_definitions.push((
+                self.visit.string_type_definitions.push((
                     expr.range(),
                     value.to_str(),
                     self.semantic.snapshot(),
                 ));
             } else {
-                self.deferred
+                self.visit
                     .future_type_definitions
                     .push((expr, self.semantic.snapshot()));
             }
@@ -945,7 +947,8 @@ where
                 }
 
                 self.semantic.push_scope(ScopeKind::Lambda(lambda));
-                self.deferred.lambdas.push(self.semantic.snapshot());
+                self.visit.lambdas.push(self.semantic.snapshot());
+                self.analyze.lambdas.push(self.semantic.snapshot());
             }
             Expr::IfExp(ast::ExprIfExp {
                 test,
@@ -1252,7 +1255,7 @@ where
             }
             Expr::StringLiteral(ast::ExprStringLiteral { value, .. }) => {
                 if self.semantic.in_type_definition() && !self.semantic.in_typing_literal() {
-                    self.deferred.string_type_definitions.push((
+                    self.visit.string_type_definitions.push((
                         expr.range(),
                         value.to_str(),
                         self.semantic.snapshot(),
@@ -1273,7 +1276,7 @@ where
             | Expr::ListComp(_)
             | Expr::DictComp(_)
             | Expr::SetComp(_) => {
-                self.deferred.scopes.push(self.semantic.scope_id);
+                self.analyze.scopes.push(self.semantic.scope_id);
                 self.semantic.pop_scope();
             }
             _ => {}
@@ -1447,7 +1450,7 @@ where
             bound: Some(bound), ..
         }) = type_param
         {
-            self.deferred
+            self.visit
                 .type_param_definitions
                 .push((bound, self.semantic.snapshot()));
         }
@@ -1809,8 +1812,8 @@ impl<'a> Checker<'a> {
 
     fn visit_deferred_future_type_definitions(&mut self) {
         let snapshot = self.semantic.snapshot();
-        while !self.deferred.future_type_definitions.is_empty() {
-            let type_definitions = std::mem::take(&mut self.deferred.future_type_definitions);
+        while !self.visit.future_type_definitions.is_empty() {
+            let type_definitions = std::mem::take(&mut self.visit.future_type_definitions);
             for (expr, snapshot) in type_definitions {
                 self.semantic.restore(snapshot);
 
@@ -1824,8 +1827,8 @@ impl<'a> Checker<'a> {
 
     fn visit_deferred_type_param_definitions(&mut self) {
         let snapshot = self.semantic.snapshot();
-        while !self.deferred.type_param_definitions.is_empty() {
-            let type_params = std::mem::take(&mut self.deferred.type_param_definitions);
+        while !self.visit.type_param_definitions.is_empty() {
+            let type_params = std::mem::take(&mut self.visit.type_param_definitions);
             for (type_param, snapshot) in type_params {
                 self.semantic.restore(snapshot);
 
@@ -1839,8 +1842,8 @@ impl<'a> Checker<'a> {
 
     fn visit_deferred_string_type_definitions(&mut self, allocator: &'a typed_arena::Arena<Expr>) {
         let snapshot = self.semantic.snapshot();
-        while !self.deferred.string_type_definitions.is_empty() {
-            let type_definitions = std::mem::take(&mut self.deferred.string_type_definitions);
+        while !self.visit.string_type_definitions.is_empty() {
+            let type_definitions = std::mem::take(&mut self.visit.string_type_definitions);
             for (range, value, snapshot) in type_definitions {
                 if let Ok((expr, kind)) =
                     parse_type_annotation(value, range, self.locator.contents())
@@ -1887,8 +1890,8 @@ impl<'a> Checker<'a> {
 
     fn visit_deferred_functions(&mut self) {
         let snapshot = self.semantic.snapshot();
-        while !self.deferred.functions.is_empty() {
-            let deferred_functions = std::mem::take(&mut self.deferred.functions);
+        while !self.visit.functions.is_empty() {
+            let deferred_functions = std::mem::take(&mut self.visit.functions);
             for snapshot in deferred_functions {
                 self.semantic.restore(snapshot);
 
@@ -1906,11 +1909,12 @@ impl<'a> Checker<'a> {
         self.semantic.restore(snapshot);
     }
 
+    /// Visit all deferred lambdas. Returns a list of snapshots, such that the caller can restore
+    /// the semantic model to the state it was in before visiting the deferred lambdas.
     fn visit_deferred_lambdas(&mut self) {
         let snapshot = self.semantic.snapshot();
-        let mut deferred: Vec<Snapshot> = Vec::with_capacity(self.deferred.lambdas.len());
-        while !self.deferred.lambdas.is_empty() {
-            let lambdas = std::mem::take(&mut self.deferred.lambdas);
+        while !self.visit.lambdas.is_empty() {
+            let lambdas = std::mem::take(&mut self.visit.lambdas);
             for snapshot in lambdas {
                 self.semantic.restore(snapshot);
 
@@ -1927,15 +1931,23 @@ impl<'a> Checker<'a> {
                     self.visit_parameters(parameters);
                 }
                 self.visit_expr(body);
-
-                deferred.push(snapshot);
             }
         }
-        // Reset the deferred lambdas, so we can analyze them later on.
-        self.deferred.lambdas = deferred;
         self.semantic.restore(snapshot);
     }
 
+    /// Recursively visit all deferred AST nodes, including lambdas, functions, and type
+    /// annotations.
+    fn visit_deferred(&mut self, allocator: &'a typed_arena::Arena<Expr>) {
+        while !self.visit.is_empty() {
+            self.visit_deferred_functions();
+            self.visit_deferred_type_param_definitions();
+            self.visit_deferred_lambdas();
+            self.visit_deferred_future_type_definitions();
+            self.visit_deferred_string_type_definitions(&allocator);
+        }
+    }
+
     /// Run any lint rules that operate over the module exports (i.e., members of `__all__`).
     fn visit_exports(&mut self) {
         let snapshot = self.semantic.snapshot();
@@ -2043,12 +2055,8 @@ pub(crate) fn check_ast(
     // Visit any deferred syntax nodes. Take care to visit in order, such that we avoid adding
     // new deferred nodes after visiting nodes of that kind. For example, visiting a deferred
     // function can add a deferred lambda, but the opposite is not true.
-    checker.visit_deferred_functions();
-    checker.visit_deferred_type_param_definitions();
-    checker.visit_deferred_lambdas();
-    checker.visit_deferred_future_type_definitions();
     let allocator = typed_arena::Arena::new();
-    checker.visit_deferred_string_type_definitions(&allocator);
+    checker.visit_deferred(&allocator);
     checker.visit_exports();
 
     // Check docstrings, bindings, and unresolved references.
@@ -2060,7 +2068,7 @@ pub(crate) fn check_ast(
 
     // Reset the scope to module-level, and check all consumed scopes.
     checker.semantic.scope_id = ScopeId::global();
-    checker.deferred.scopes.push(ScopeId::global());
+    checker.analyze.scopes.push(ScopeId::global());
     analyze::deferred_scopes(&mut checker);
 
     checker.diagnostics

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

@@ -54,6 +54,7 @@ mod tests {
     #[test_case(Rule::UnusedImport, Path::new("F401_19.py"))]
     #[test_case(Rule::UnusedImport, Path::new("F401_20.py"))]
     #[test_case(Rule::UnusedImport, Path::new("F401_21.py"))]
+    #[test_case(Rule::UnusedImport, Path::new("F401_22.py"))]
     #[test_case(Rule::ImportShadowedByLoopVar, Path::new("F402.py"))]
     #[test_case(Rule::ImportShadowedByLoopVar, Path::new("F402.ipynb"))]
     #[test_case(Rule::UndefinedLocalWithImportStar, Path::new("F403.py"))]

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F401_F401_22.py.snap

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