add support for match statement (#630)

Author: asottile

pyflakes/checker.py

@@ -275,7 +275,8 @@ def iter_child_nodes(node, omit=None, _fields_order=_FieldsOrder()):
             yield field
         elif isinstance(field, list):
             for item in field:
-                yield item
+                if isinstance(item, ast.AST):
+                    yield item
 
 
 def convert_to_value(item):
@@ -691,6 +692,8 @@ def getNodeName(node):
         return node.id
     if hasattr(node, 'name'):   # an ExceptHandler node
         return node.name
+    if hasattr(node, 'rest'):   # a MatchMapping node
+        return node.rest
 
 
 TYPING_MODULES = frozenset(('typing', 'typing_extensions'))
@@ -2378,3 +2381,12 @@ def COMPARE(self, node):
             left = right
 
         self.handleChildren(node)
+
+    MATCH = MATCH_CASE = MATCHCLASS = MATCHOR = MATCHSEQUENCE = handleChildren
+    MATCHSINGLETON = MATCHVALUE = handleChildren
+
+    def _match_target(self, node):
+        self.handleNodeStore(node)
+        self.handleChildren(node)
+
+    MATCHAS = MATCHMAPPING = MATCHSTAR = _match_target

pyflakes/test/test_match.py

@@ -0,0 +1,83 @@
+from sys import version_info
+
+from pyflakes.test.harness import TestCase, skipIf
+
+
+@skipIf(version_info < (3, 10), "Python >= 3.10 only")
+class TestMatch(TestCase):
+    def test_match_bindings(self):
+        self.flakes('''
+            def f():
+                x = 1
+                match x:
+                    case 1 as y:
+                        print(f'matched as {y}')
+        ''')
+        self.flakes('''
+            def f():
+                x = [1, 2, 3]
+                match x:
+                    case [1, y, 3]:
+                        print(f'matched {y}')
+        ''')
+        self.flakes('''
+            def f():
+                x = {'foo': 1}
+                match x:
+                    case {'foo': y}:
+                        print(f'matched {y}')
+        ''')
+
+    def test_match_pattern_matched_class(self):
+        self.flakes('''
+            from a import B
+
+            match 1:
+                case B(x=1) as y:
+                    print(f'matched {y}')
+        ''')
+        self.flakes('''
+            from a import B
+
+            match 1:
+                case B(a, x=z) as y:
+                    print(f'matched {y} {a} {z}')
+        ''')
+
+    def test_match_placeholder(self):
+        self.flakes('''
+            def f():
+                match 1:
+                    case _:
+                        print('catchall!')
+        ''')
+
+    def test_match_singleton(self):
+        self.flakes('''
+            match 1:
+                case True:
+                    print('true')
+        ''')
+
+    def test_match_or_pattern(self):
+        self.flakes('''
+            match 1:
+                case 1 | 2:
+                    print('one or two')
+        ''')
+
+    def test_match_star(self):
+        self.flakes('''
+            x = [1, 2, 3]
+            match x:
+                case [1, *y]:
+                    print(f'captured: {y}')
+        ''')
+
+    def test_match_double_star(self):
+        self.flakes('''
+            x = {'foo': 'bar', 'baz': 'womp'}
+            match x:
+                case {'foo': k1, **rest}:
+                    print(f'{k1=} {rest=}')
+        ''')