PEP 585: allow builtins to be generic (#9564)

Resolves #7907

Co-authored-by: cdce8p <30130371+cdce8p@users.noreply.github.com>
Co-authored-by: Ethan Smith <ethan@ethanhs.me>
Co-authored-by: hauntsaninja <>

mypy/nodes.py

@@ -138,11 +138,17 @@ def get_column(self) -> int:
     'builtins.frozenset': 'typing.FrozenSet',
 }  # type: Final
 
-nongen_builtins = {'builtins.tuple': 'typing.Tuple',
-                   'builtins.enumerate': ''}  # type: Final
-nongen_builtins.update((name, alias) for alias, name in type_aliases.items())
+_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']
+del _nongen_builtins['collections.OrderedDict']
+
+
+def get_nongen_builtins(python_version: Tuple[int, int]) -> Dict[str, str]:
+    # After 3.9 with pep585 generic builtins are allowed.
+    return _nongen_builtins if python_version < (3, 9) else {}
+
 
 RUNTIME_PROTOCOL_DECOS = ('typing.runtime_checkable',
                           'typing_extensions.runtime',

mypy/semanal.py

@@ -73,7 +73,7 @@
     YieldExpr, ExecStmt, BackquoteExpr, ImportBase, AwaitExpr,
     IntExpr, FloatExpr, UnicodeExpr, TempNode, OverloadPart,
     PlaceholderNode, COVARIANT, CONTRAVARIANT, INVARIANT,
-    nongen_builtins, get_member_expr_fullname, REVEAL_TYPE,
+    get_nongen_builtins, get_member_expr_fullname, REVEAL_TYPE,
     REVEAL_LOCALS, is_final_node, TypedDictExpr, type_aliases_source_versions,
     EnumCallExpr, RUNTIME_PROTOCOL_DECOS, FakeExpression, Statement, AssignmentExpr,
     ParamSpecExpr
@@ -465,7 +465,7 @@ def add_builtin_aliases(self, tree: MypyFile) -> None:
                     target = self.named_type_or_none(target_name, [])
                     assert target is not None
                     # Transform List to List[Any], etc.
-                    fix_instance_types(target, self.fail, self.note)
+                    fix_instance_types(target, self.fail, self.note, self.options.python_version)
                     alias_node = TypeAlias(target, alias,
                                            line=-1, column=-1,  # there is no context
                                            no_args=True, normalized=True)
@@ -2589,7 +2589,7 @@ def check_and_set_up_type_alias(self, s: AssignmentStmt) -> bool:
         # if the expected number of arguments is non-zero, so that aliases like A = List work.
         # However, eagerly expanding aliases like Text = str is a nice performance optimization.
         no_args = isinstance(res, Instance) and not res.args  # type: ignore
-        fix_instance_types(res, self.fail, self.note)
+        fix_instance_types(res, self.fail, self.note, self.options.python_version)
         alias_node = TypeAlias(res, self.qualified_name(lvalue.name), s.line, s.column,
                                alias_tvars=alias_tvars, no_args=no_args)
         if isinstance(s.rvalue, (IndexExpr, CallExpr)):  # CallExpr is for `void = type(None)`
@@ -3807,12 +3807,13 @@ def analyze_type_application(self, expr: IndexExpr) -> None:
             if isinstance(target, Instance):
                 name = target.type.fullname
                 if (alias.no_args and  # this avoids bogus errors for already reported aliases
-                        name in nongen_builtins and not alias.normalized):
+                        name in get_nongen_builtins(self.options.python_version) and
+                        not alias.normalized):
                     self.fail(no_subscript_builtin_alias(name, propose_alt=False), expr)
         # ...or directly.
         else:
             n = self.lookup_type_node(base)
-            if n and n.fullname in nongen_builtins:
+            if n and n.fullname in get_nongen_builtins(self.options.python_version):
                 self.fail(no_subscript_builtin_alias(n.fullname, propose_alt=False), expr)
 
     def analyze_type_application_args(self, expr: IndexExpr) -> Optional[List[Type]]:

mypy/test/testcheck.py

@@ -66,7 +66,6 @@
     'check-selftype.test',
     'check-python2.test',
     'check-columns.test',
-    'check-future.test',
     'check-functions.test',
     'check-tuples.test',
     'check-expressions.test',
@@ -92,6 +91,7 @@
     'check-errorcodes.test',
     'check-annotated.test',
     'check-parameter-specification.test',
+    'check-generic-alias.test',
 ]
 
 # Tests that use Python 3.8-only AST features (like expression-scoped ignores):

mypy/typeanal.py

@@ -21,7 +21,7 @@
 
 from mypy.nodes import (
     TypeInfo, Context, SymbolTableNode, Var, Expression,
-    nongen_builtins, check_arg_names, check_arg_kinds, ARG_POS, ARG_NAMED,
+    get_nongen_builtins, check_arg_names, check_arg_kinds, ARG_POS, ARG_NAMED,
     ARG_OPT, ARG_NAMED_OPT, ARG_STAR, ARG_STAR2, TypeVarExpr, TypeVarLikeExpr, ParamSpecExpr,
     TypeAlias, PlaceholderNode, SYMBOL_FUNCBASE_TYPES, Decorator, MypyFile
 )
@@ -94,6 +94,8 @@ def analyze_type_alias(node: Expression,
 
 def no_subscript_builtin_alias(name: str, propose_alt: bool = True) -> str:
     msg = '"{}" is not subscriptable'.format(name.split('.')[-1])
+    # This should never be called if the python_version is 3.9 or newer
+    nongen_builtins = get_nongen_builtins((3, 8))
     replacement = nongen_builtins[name]
     if replacement and propose_alt:
         msg += ', use "{}" instead'.format(replacement)
@@ -194,7 +196,7 @@ def visit_unbound_type_nonoptional(self, t: UnboundType, defining_literal: bool)
             hook = self.plugin.get_type_analyze_hook(fullname)
             if hook is not None:
                 return hook(AnalyzeTypeContext(t, t, self))
-            if (fullname in nongen_builtins
+            if (fullname in get_nongen_builtins(self.options.python_version)
                     and t.args and
                     not self.allow_unnormalized and
                     not self.api.is_future_flag_set("annotations")):
@@ -241,6 +243,7 @@ def visit_unbound_type_nonoptional(self, t: UnboundType, defining_literal: bool)
                         self.fail,
                         self.note,
                         disallow_any=disallow_any,
+                        python_version=self.options.python_version,
                         use_generic_error=True,
                         unexpanded_type=t)
                 return res
@@ -272,7 +275,9 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Opt
             self.fail("Final can be only used as an outermost qualifier"
                       " in a variable annotation", t)
             return AnyType(TypeOfAny.from_error)
-        elif fullname == 'typing.Tuple':
+        elif (fullname == 'typing.Tuple' or
+             (fullname == 'builtins.tuple' and (self.options.python_version >= (3, 9) or
+                                                self.api.is_future_flag_set('annotations')))):
             # Tuple is special because it is involved in builtin import cycle
             # and may be not ready when used.
             sym = self.api.lookup_fully_qualified_or_none('builtins.tuple')
@@ -305,7 +310,8 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Opt
         elif fullname == 'typing.Callable':
             return self.analyze_callable_type(t)
         elif (fullname == 'typing.Type' or
-             (fullname == 'builtins.type' and self.api.is_future_flag_set('annotations'))):
+             (fullname == 'builtins.type' and (self.options.python_version >= (3, 9) or
+                                               self.api.is_future_flag_set('annotations')))):
             if len(t.args) == 0:
                 if fullname == 'typing.Type':
                     any_type = self.get_omitted_any(t)
@@ -342,7 +348,8 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Opt
 
     def get_omitted_any(self, typ: Type, fullname: Optional[str] = None) -> AnyType:
         disallow_any = not self.is_typeshed_stub and self.options.disallow_any_generics
-        return get_omitted_any(disallow_any, self.fail, self.note, typ, fullname)
+        return get_omitted_any(disallow_any, self.fail, self.note, typ,
+                               self.options.python_version, fullname)
 
     def analyze_type_with_type_info(
             self, info: TypeInfo, args: Sequence[Type], ctx: Context) -> Type:
@@ -364,7 +371,8 @@ def analyze_type_with_type_info(
         if len(instance.args) != len(info.type_vars) and not self.defining_alias:
             fix_instance(instance, self.fail, self.note,
                          disallow_any=self.options.disallow_any_generics and
-                         not self.is_typeshed_stub)
+                         not self.is_typeshed_stub,
+                         python_version=self.options.python_version)
 
         tup = info.tuple_type
         if tup is not None:
@@ -979,9 +987,11 @@ def tuple_type(self, items: List[Type]) -> TupleType:
 
 
 def get_omitted_any(disallow_any: bool, fail: MsgCallback, note: MsgCallback,
-                    orig_type: Type, fullname: Optional[str] = None,
+                    orig_type: Type, python_version: Tuple[int, int],
+                    fullname: Optional[str] = None,
                     unexpanded_type: Optional[Type] = None) -> AnyType:
     if disallow_any:
+        nongen_builtins = get_nongen_builtins(python_version)
         if fullname in nongen_builtins:
             typ = orig_type
             # We use a dedicated error message for builtin generics (as the most common case).
@@ -1019,7 +1029,8 @@ def get_omitted_any(disallow_any: bool, fail: MsgCallback, note: MsgCallback,
 
 
 def fix_instance(t: Instance, fail: MsgCallback, note: MsgCallback,
-                 disallow_any: bool, use_generic_error: bool = False,
+                 disallow_any: bool, python_version: Tuple[int, int],
+                 use_generic_error: bool = False,
                  unexpanded_type: Optional[Type] = None,) -> None:
     """Fix a malformed instance by replacing all type arguments with Any.
 
@@ -1030,7 +1041,8 @@ def fix_instance(t: Instance, fail: MsgCallback, note: MsgCallback,
             fullname = None  # type: Optional[str]
         else:
             fullname = t.type.fullname
-        any_type = get_omitted_any(disallow_any, fail, note, t, fullname, unexpanded_type)
+        any_type = get_omitted_any(disallow_any, fail, note, t, python_version, fullname,
+                                   unexpanded_type)
         t.args = (any_type,) * len(t.type.type_vars)
         return
     # Invalid number of type parameters.
@@ -1289,21 +1301,26 @@ def make_optional_type(t: Type) -> Type:
         return UnionType([t, NoneType()], t.line, t.column)
 
 
-def fix_instance_types(t: Type, fail: MsgCallback, note: MsgCallback) -> None:
+def fix_instance_types(t: Type, fail: MsgCallback, note: MsgCallback,
+                       python_version: Tuple[int, int]) -> None:
     """Recursively fix all instance types (type argument count) in a given type.
 
     For example 'Union[Dict, List[str, int]]' will be transformed into
     'Union[Dict[Any, Any], List[Any]]' in place.
     """
-    t.accept(InstanceFixer(fail, note))
+    t.accept(InstanceFixer(fail, note, python_version))
 
 
 class InstanceFixer(TypeTraverserVisitor):
-    def __init__(self, fail: MsgCallback, note: MsgCallback) -> None:
+    def __init__(
+        self, fail: MsgCallback, note: MsgCallback, python_version: Tuple[int, int]
+    ) -> None:
         self.fail = fail
         self.note = note
+        self.python_version = python_version
 
     def visit_instance(self, typ: Instance) -> None:
         super().visit_instance(typ)
         if len(typ.args) != len(typ.type.type_vars):
-            fix_instance(typ, self.fail, self.note, disallow_any=False, use_generic_error=True)
+            fix_instance(typ, self.fail, self.note, disallow_any=False,
+                         python_version=self.python_version, use_generic_error=True)