Treat each match case as a separate scope

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

@@ -14,13 +14,26 @@ def f():
             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

@@ -119,5 +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

@@ -10,8 +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, Pattern, PatternKind, Stmt, StmtKind,
-    Suite,
+    ExprKind, KeywordData, Located, Location, MatchCase, Operator, Pattern, PatternKind, Stmt,
+    StmtKind, Suite,
 };
 use rustpython_parser::parser;
 use smallvec::smallvec;
@@ -29,7 +29,7 @@ use crate::ast::types::{
     RefEquality, Scope, ScopeKind,
 };
 use crate::ast::typing::{match_annotated_subscript, Callable, SubscriptKind};
-use crate::ast::visitor::{walk_excepthandler, walk_pattern, 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};
@@ -3841,6 +3841,14 @@ 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), ..

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

@@ -2,14 +2,36 @@
 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: 22
+    row: 26
     column: 19
   end_location:
-    row: 22
+    row: 26
     column: 27
   fix: ~
   parent: ~

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

@@ -194,6 +194,35 @@ expression: diagnostics
     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

@@ -230,6 +230,17 @@ expression: diagnostics
     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: ~