python · msullivan · Oct 19, 2020 · Aug 31, 2020 · Oct 19, 2020 · Oct 19, 2020
diff --git a/mypy/nodes.py b/mypy/nodes.py
@@ -114,11 +114,12 @@ def get_column(self) -> int:
     'typing.Counter': 'collections.Counter',
     'typing.DefaultDict': 'collections.defaultdict',
     'typing.Deque': 'collections.deque',
+    'typing.OrderedDict': 'collections.OrderedDict',
 }  # type: Final
 
 # This keeps track of the oldest supported Python version where the corresponding
-# alias _target_ is available.
-type_aliases_target_versions = {
+# alias source is available.
+type_aliases_source_versions = {
     'typing.List': (2, 7),
     'typing.Dict': (2, 7),
     'typing.Set': (2, 7),
@@ -127,6 +128,7 @@ def get_column(self) -> int:
     'typing.Counter': (2, 7),
     'typing.DefaultDict': (2, 7),
     'typing.Deque': (2, 7),
+    'typing.OrderedDict': (3, 7),
 }  # type: Final
 
 reverse_builtin_aliases = {
@@ -139,6 +141,8 @@ def get_column(self) -> int:
 nongen_builtins = {'builtins.tuple': 'typing.Tuple',
                    'builtins.enumerate': ''}  # type: Final
 nongen_builtins.update((name, alias) for alias, name in type_aliases.items())
+# Drop OrderedDict from this for backward compatibility
+del nongen_builtins['collections.OrderedDict']
 
 RUNTIME_PROTOCOL_DECOS = ('typing.runtime_checkable',
                           'typing_extensions.runtime',

diff --git a/mypy/semanal.py b/mypy/semanal.py
@@ -74,7 +74,7 @@
     IntExpr, FloatExpr, UnicodeExpr, TempNode, OverloadPart,
     PlaceholderNode, COVARIANT, CONTRAVARIANT, INVARIANT,
     nongen_builtins, get_member_expr_fullname, REVEAL_TYPE,
-    REVEAL_LOCALS, is_final_node, TypedDictExpr, type_aliases_target_versions,
+    REVEAL_LOCALS, is_final_node, TypedDictExpr, type_aliases_source_versions,
     EnumCallExpr, RUNTIME_PROTOCOL_DECOS, FakeExpression, Statement, AssignmentExpr,
     ParamSpecExpr
 )
@@ -307,12 +307,27 @@ def prepare_typing_namespace(self, file_node: MypyFile) -> None:
 
         They will be replaced with real aliases when corresponding targets are ready.
         """
-        for stmt in file_node.defs.copy():
-            if (isinstance(stmt, AssignmentStmt) and len(stmt.lvalues) == 1 and
-                    isinstance(stmt.lvalues[0], NameExpr)):
-                # Assignment to a simple name, remove it if it is a dummy alias.
-                if 'typing.' + stmt.lvalues[0].name in type_aliases:
-                    file_node.defs.remove(stmt)
+        # This is all pretty unfortunate. typeshed now has a
+        # sys.version_info check for OrderedDict, and we shouldn't
+        # take it out, because it is correct and a typechecker should
+        # use that as a source of truth. But instead we rummage
+        # through IfStmts to remove the info first.  (I tried to
+        # remove this whole machinery and ran into issues with the
+        # builtins/typing import cycle.)
+        def helper(defs: List[Statement]) -> None:
+            for stmt in defs.copy():
+                if isinstance(stmt, IfStmt):
+                    for body in stmt.body:
+                        helper(body.body)
+                    if stmt.else_body:
+                        helper(stmt.else_body.body)
+                if (isinstance(stmt, AssignmentStmt) and len(stmt.lvalues) == 1 and
+                        isinstance(stmt.lvalues[0], NameExpr)):
+                    # Assignment to a simple name, remove it if it is a dummy alias.
+                    if 'typing.' + stmt.lvalues[0].name in type_aliases:
+                        defs.remove(stmt)
+
+        helper(file_node.defs)
 
     def prepare_builtins_namespace(self, file_node: MypyFile) -> None:
         """Add certain special-cased definitions to the builtins module.
@@ -430,7 +445,7 @@ def add_builtin_aliases(self, tree: MypyFile) -> None:
         """
         assert tree.fullname == 'typing'
         for alias, target_name in type_aliases.items():
-            if type_aliases_target_versions[alias] > self.options.python_version:
+            if type_aliases_source_versions[alias] > self.options.python_version:
                 # This alias is not available on this Python version.
                 continue
             name = alias.split('.')[-1]