Treat each match case as a separate scope

crates/ruff/resources/test/fixtures/pyflakes/F821_9.py

@@ -0,0 +1,39 @@
+"""Test: match statements."""
+from dataclasses import dataclass
+
+
+@dataclass
+class Car:
+    make: str
+    model: str
+
+
+def f():
+    match Car("Toyota", "Corolla"):
+        case Car("Toyota", model):
+            print(model)
+        case Car(make, "Corolla"):
+            print(make)
+        case Car(_, _):
+            print(make, model)
+        case _:
+            print("No match")
+
+
+def f(provided: int) -> int:
+    match provided:
+        case True:
+            return captured  # F821
+        case [*_] as captured:
+            return captured
+        case [captured, *_]:
+            return captured
+        case captured:
+            return captured
+
+
+match 1:
+    case 1:
+        x = 1
+
+print(x)

crates/ruff/resources/test/fixtures/pyflakes/F841_0.py

@@ -119,3 +119,7 @@ def f(x: int):
             print("A")
         case [Bar.A, *_]:
             print("A")
+        case [*_] as y:
+            z = 1
+        case y:
+            pass

crates/ruff/src/ast/types.rs

@@ -78,6 +78,7 @@ pub enum ScopeKind<'a> {
     Generator,
     Module,
     Lambda(Lambda<'a>),
+    Case,
 }
 
 #[derive(Debug)]

crates/ruff/src/checkers/ast.rs

@@ -10,7 +10,8 @@ use rustc_hash::{FxHashMap, FxHashSet};
 use rustpython_common::cformat::{CFormatError, CFormatErrorType};
 use rustpython_parser::ast::{
     Arg, Arguments, Comprehension, Constant, Excepthandler, ExcepthandlerKind, Expr, ExprContext,
-    ExprKind, KeywordData, Located, Location, Operator, Stmt, StmtKind, Suite,
+    ExprKind, KeywordData, Located, Location, MatchCase, Operator, Pattern, PatternKind, Stmt,
+    StmtKind, Suite,
 };
 use rustpython_parser::parser;
 use smallvec::smallvec;
@@ -28,7 +29,7 @@ use crate::ast::types::{
     RefEquality, Scope, ScopeKind,
 };
 use crate::ast::typing::{match_annotated_subscript, Callable, SubscriptKind};
-use crate::ast::visitor::{walk_excepthandler, Visitor};
+use crate::ast::visitor::{walk_excepthandler, walk_match_case, walk_pattern, Visitor};
 use crate::ast::{branch_detection, cast, helpers, operations, typing, visitor};
 use crate::docstrings::definition::{Definition, DefinitionKind, Docstring, Documentable};
 use crate::registry::{Diagnostic, Rule};
@@ -3840,6 +3841,36 @@ where
         }
     }
 
+    fn visit_match_case(&mut self, match_case: &'b MatchCase) {
+        self.push_scope(Scope::new(ScopeKind::Case));
+        walk_match_case(self, match_case);
+        self.deferred_assignments
+            .push((self.scope_stack.clone(), self.parents.clone()));
+        self.pop_scope();
+    }
+
+    fn visit_pattern(&mut self, pattern: &'b Pattern) {
+        if let PatternKind::MatchAs {
+            name: Some(name), ..
+        } = &pattern.node
+        {
+            self.add_binding(
+                name,
+                Binding {
+                    kind: BindingKind::Assignment,
+                    runtime_usage: None,
+                    synthetic_usage: None,
+                    typing_usage: None,
+                    range: Range::from_located(pattern),
+                    source: Some(self.current_stmt().clone()),
+                    context: self.execution_context(),
+                },
+            );
+        }
+
+        walk_pattern(self, pattern);
+    }
+
     fn visit_format_spec(&mut self, format_spec: &'b Expr) {
         match &format_spec.node {
             ExprKind::JoinedStr { values } => {

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

@@ -101,6 +101,7 @@ mod tests {
     #[test_case(Rule::UndefinedName, Path::new("F821_6.py"); "F821_6")]
     #[test_case(Rule::UndefinedName, Path::new("F821_7.py"); "F821_7")]
     #[test_case(Rule::UndefinedName, Path::new("F821_8.pyi"); "F821_8")]
+    #[test_case(Rule::UndefinedName, Path::new("F821_9.py"); "F821_9")]
     #[test_case(Rule::UndefinedExport, Path::new("F822_0.py"); "F822_0")]
     #[test_case(Rule::UndefinedExport, Path::new("F822_1.py"); "F822_1")]
     #[test_case(Rule::UndefinedExport, Path::new("F822_2.py"); "F822_2")]

crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__F821_F821_9.py.snap

@@ -0,0 +1,38 @@
+---
+source: crates/ruff/src/rules/pyflakes/mod.rs
+expression: diagnostics
+---
+- kind:
+    UndefinedName:
+      name: make
+  location:
+    row: 18
+    column: 18
+  end_location:
+    row: 18
+    column: 22
+  fix: ~
+  parent: ~
+- kind:
+    UndefinedName:
+      name: model
+  location:
+    row: 18
+    column: 24
+  end_location:
+    row: 18
+    column: 29
+  fix: ~
+  parent: ~
+- kind:
+    UndefinedName:
+      name: captured
+  location:
+    row: 26
+    column: 19
+  end_location:
+    row: 26
+    column: 27
+  fix: ~
+  parent: ~
+

crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__F841_F841_0.py.snap

@@ -186,4 +186,44 @@ expression: diagnostics
       row: 115
       column: 10
   parent: ~
+- kind:
+    UnusedVariable:
+      name: y
+  location:
+    row: 122
+    column: 13
+  end_location:
+    row: 122
+    column: 22
+  fix: ~
+  parent: ~
+- kind:
+    UnusedVariable:
+      name: z
+  location:
+    row: 123
+    column: 12
+  end_location:
+    row: 123
+    column: 13
+  fix:
+    content: pass
+    location:
+      row: 123
+      column: 12
+    end_location:
+      row: 123
+      column: 17
+  parent: ~
+- kind:
+    UnusedVariable:
+      name: y
+  location:
+    row: 124
+    column: 13
+  end_location:
+    row: 124
+    column: 14
+  fix: ~
+  parent: ~
 

crates/ruff/src/rules/pyflakes/snapshots/ruff__rules__pyflakes__tests__f841_dummy_variable_rgx.snap

@@ -222,4 +222,26 @@ expression: diagnostics
       row: 115
       column: 10
   parent: ~
+- kind:
+    UnusedVariable:
+      name: y
+  location:
+    row: 122
+    column: 13
+  end_location:
+    row: 122
+    column: 22
+  fix: ~
+  parent: ~
+- kind:
+    UnusedVariable:
+      name: y
+  location:
+    row: 124
+    column: 13
+  end_location:
+    row: 124
+    column: 14
+  fix: ~
+  parent: ~