Fix: elif and else branches should not be affected.

Author: PetterS

pyflakes/checker.py

@@ -1852,9 +1852,17 @@ def IF(self, node):
         prev = self._in_type_checking
         if _is_typing(node.test, 'TYPE_CHECKING', self.scopeStack):
             self._in_type_checking = True
-        self.handleChildren(node)
+        # Handle the body of this if statement.
+        body_nodes = node.body
+        if not isinstance(body_nodes, list):
+            body_nodes = [body_nodes]
+        for body_node in body_nodes:
+            self.handleNode(body_node, node)
         self._in_type_checking = prev
 
+        # Handle the test of the if statement (elif, else).
+        self.handleChildren(node, omit=["body"])
+
     IFEXP = IF
 
     def ASSERT(self, node):

pyflakes/test/test_type_annotations.py

@@ -596,3 +596,23 @@ class C(Protocol):
                 def f():  # type: () -> int
                     pass
         """)
+
+    def test_typing_guard_with_elif_branch(self):
+        # This test will actually not raise an error, even though it by analysis can
+        # be shown to have an error (Protocol is not defined outside TYPE_CHECKING).
+        # Pyflakes currently does not to case analysis.
+
+        self.flakes("""
+            from typing import TYPE_CHECKING
+
+            if TYPE_CHECKING:
+                from typing import Protocol
+            elif False:
+                Protocol = object
+            else:
+                pass
+
+            class C(Protocol):
+                def f():  # type: () -> int
+                    pass
+        """)