allow redefinition of functions across match arms (#772)

Author: asottile

pyflakes/checker.py

@@ -29,8 +29,10 @@
 def getAlternatives(n):
     if isinstance(n, ast.If):
         return [n.body]
-    if isinstance(n, ast.Try):
+    elif isinstance(n, ast.Try):
         return [n.body + n.orelse] + [[hdl] for hdl in n.handlers]
+    elif sys.version_info >= (3, 10) and isinstance(n, ast.Match):
+        return [mc.body for mc in n.cases]
 
 
 FOR_TYPES = (ast.For, ast.AsyncFor)

pyflakes/test/test_match.py

@@ -81,3 +81,14 @@ def test_match_double_star(self):
                 case {'foo': k1, **rest}:
                     print(f'{k1=} {rest=}')
         ''')
+
+    def test_defined_in_different_branches(self):
+        self.flakes('''
+            def f(x):
+                match x:
+                    case 1:
+                        def y(): pass
+                    case _:
+                        def y(): print(1)
+                return y
+        ''')