Generalize X[()] support for Unpack with empty tuples

mypy/checkexpr.py

@@ -4896,7 +4896,7 @@ class C(Generic[T, Unpack[Ts]]): ...
         # This code can be only called either from checking a type application, or from
         # checking a type alias (after the caller handles no_args aliases), so we know it
         # was initially an IndexExpr, and we allow empty tuple type arguments.
-        if not validate_instance(fake, self.chk.fail, empty_tuple_index=True):
+        if not validate_instance(fake, self.chk.fail, has_parameters=True):
             fix_instance(
                 fake, self.chk.fail, self.chk.note, disallow_any=False, options=self.chk.options
             )

mypy/exprtotype.py

@@ -129,8 +129,7 @@ def expr_to_unanalyzed_type(
                 expr_to_unanalyzed_type(arg, options, allow_new_syntax, expr, allow_unpack=True)
                 for arg in args
             )
-            if not base.args:
-                base.empty_tuple_index = True
+            base.has_parameters = True
             return base
         else:
             raise TypeTranslationError()

mypy/fastparse.py

@@ -2063,22 +2063,15 @@ def visit_Slice(self, n: ast3.Slice) -> Type:
 
     # Subscript(expr value, expr slice, expr_context ctx)  # Python 3.9 and later
     def visit_Subscript(self, n: ast3.Subscript) -> Type:
-        empty_tuple_index = False
         if isinstance(n.slice, ast3.Tuple):
             params = self.translate_expr_list(n.slice.elts)
-            if len(n.slice.elts) == 0:
-                empty_tuple_index = True
         else:
             params = [self.visit(n.slice)]
 
         value = self.visit(n.value)
         if isinstance(value, UnboundType) and not value.args:
             return UnboundType(
-                value.name,
-                params,
-                line=self.line,
-                column=value.column,
-                empty_tuple_index=empty_tuple_index,
+                value.name, params, line=self.line, column=value.column, has_parameters=True
             )
         else:
             return self.invalid_type(n)

mypy/semanal.py

@@ -3933,8 +3933,8 @@ def analyze_alias(
             new_tvar_defs.append(td)
 
         qualified_tvars = [node.fullname for _name, node in alias_type_vars]
-        empty_tuple_index = typ.empty_tuple_index if isinstance(typ, UnboundType) else False
-        return analyzed, new_tvar_defs, depends_on, qualified_tvars, empty_tuple_index
+        has_parameters = typ.has_parameters if isinstance(typ, UnboundType) else False
+        return analyzed, new_tvar_defs, depends_on, qualified_tvars, has_parameters
 
     def is_pep_613(self, s: AssignmentStmt) -> bool:
         if s.unanalyzed_type is not None and isinstance(s.unanalyzed_type, UnboundType):
@@ -4030,10 +4030,10 @@ def check_and_set_up_type_alias(self, s: AssignmentStmt) -> bool:
             alias_tvars: list[TypeVarLikeType] = []
             depends_on: set[str] = set()
             qualified_tvars: list[str] = []
-            empty_tuple_index = False
+            has_parameters = False
         else:
             tag = self.track_incomplete_refs()
-            res, alias_tvars, depends_on, qualified_tvars, empty_tuple_index = self.analyze_alias(
+            res, alias_tvars, depends_on, qualified_tvars, has_parameters = self.analyze_alias(
                 lvalue.name,
                 rvalue,
                 allow_placeholder=True,
@@ -4080,12 +4080,12 @@ def check_and_set_up_type_alias(self, s: AssignmentStmt) -> bool:
             isinstance(res, ProperType)
             and isinstance(res, Instance)
             and not res.args
-            and not empty_tuple_index
+            and not (has_parameters and res.type.type_vars)
             and not pep_695
             and not pep_613
         )
         if isinstance(res, ProperType) and isinstance(res, Instance):
-            if not validate_instance(res, self.fail, empty_tuple_index):
+            if not validate_instance(res, self.fail, has_parameters):
                 fix_instance(res, self.fail, self.note, disallow_any=False, options=self.options)
         # Aliases defined within functions can't be accessed outside
         # the function, since the symbol table will no longer
@@ -5550,7 +5550,7 @@ def visit_type_alias_stmt(self, s: TypeAliasStmt) -> None:
                 return
 
             tag = self.track_incomplete_refs()
-            res, alias_tvars, depends_on, qualified_tvars, empty_tuple_index = self.analyze_alias(
+            res, alias_tvars, depends_on, qualified_tvars, has_parameters = self.analyze_alias(
                 s.name.name,
                 s.value.expr(),
                 allow_placeholder=True,

mypy/server/astdiff.py

@@ -363,7 +363,7 @@ def visit_unbound_type(self, typ: UnboundType) -> SnapshotItem:
             "UnboundType",
             typ.name,
             typ.optional,
-            typ.empty_tuple_index,
+            typ.has_parameters,
             snapshot_types(typ.args),
         )
 

mypy/stubutil.py

@@ -279,7 +279,7 @@ def visit_unbound_type(self, t: UnboundType) -> str:
             self.stubgen.import_tracker.require_name(s)
         if t.args:
             s += f"[{self.args_str(t.args)}]"
-        elif t.empty_tuple_index:
+        elif t.has_parameters:
             s += "[()]"
         return s
 

mypy/typeanal.py

@@ -483,15 +483,15 @@ def visit_unbound_type_nonoptional(self, t: UnboundType, defining_literal: bool)
                     self.options,
                     unexpanded_type=t,
                     disallow_any=disallow_any,
-                    empty_tuple_index=t.empty_tuple_index,
+                    has_parameters=t.has_parameters,
                 )
                 # The only case where instantiate_type_alias() can return an incorrect instance is
                 # when it is top-level instance, so no need to recurse.
                 if (
                     isinstance(res, ProperType)
                     and isinstance(res, Instance)
                     and not (self.defining_alias and self.nesting_level == 0)
-                    and not validate_instance(res, self.fail, t.empty_tuple_index)
+                    and not validate_instance(res, self.fail, t.has_parameters)
                 ):
                     fix_instance(
                         res,
@@ -506,7 +506,7 @@ def visit_unbound_type_nonoptional(self, t: UnboundType, defining_literal: bool)
                     res = get_proper_type(res)
                 return res
             elif isinstance(node, TypeInfo):
-                return self.analyze_type_with_type_info(node, t.args, t, t.empty_tuple_index)
+                return self.analyze_type_with_type_info(node, t.args, t, t.has_parameters)
             elif node.fullname in TYPE_ALIAS_NAMES:
                 return AnyType(TypeOfAny.special_form)
             # Concatenate is an operator, no need for a proper type
@@ -629,7 +629,7 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Typ
                 else:
                     self.fail('Name "tuple" is not defined', t)
                 return AnyType(TypeOfAny.special_form)
-            if len(t.args) == 0 and not t.empty_tuple_index:
+            if len(t.args) == 0 and not t.has_parameters:
                 # Bare 'Tuple' is same as 'tuple'
                 any_type = self.get_omitted_any(t)
                 return self.named_type("builtins.tuple", [any_type], line=t.line, column=t.column)
@@ -815,7 +815,7 @@ def check_and_warn_deprecated(self, info: TypeInfo, ctx: Context) -> None:
                 warn(deprecated, ctx, code=codes.DEPRECATED)
 
     def analyze_type_with_type_info(
-        self, info: TypeInfo, args: Sequence[Type], ctx: Context, empty_tuple_index: bool
+        self, info: TypeInfo, args: Sequence[Type], ctx: Context, has_parameters: bool
     ) -> Type:
         """Bind unbound type when were able to find target TypeInfo.
 
@@ -853,7 +853,7 @@ def analyze_type_with_type_info(
         # Check type argument count.
         instance.args = tuple(flatten_nested_tuples(instance.args))
         if not (self.defining_alias and self.nesting_level == 0) and not validate_instance(
-            instance, self.fail, empty_tuple_index
+            instance, self.fail, has_parameters
         ):
             fix_instance(
                 instance,
@@ -2121,7 +2121,7 @@ def instantiate_type_alias(
     unexpanded_type: Type | None = None,
     disallow_any: bool = False,
     use_standard_error: bool = False,
-    empty_tuple_index: bool = False,
+    has_parameters: bool = False,
 ) -> Type:
     """Create an instance of a (generic) type alias from alias node and type arguments.
 
@@ -2149,7 +2149,7 @@ def instantiate_type_alias(
     if (
         max_tv_count > 0
         and act_len == 0
-        and not (empty_tuple_index and node.tvar_tuple_index is not None)
+        and not (has_parameters and node.tvar_tuple_index is not None)
     ):
         # Interpret bare Alias same as normal generic, i.e., Alias[Any, Any, ...]
         return set_any_tvars(
@@ -2466,7 +2466,7 @@ def make_optional_type(t: Type) -> Type:
         return UnionType([t, NoneType()], t.line, t.column)
 
 
-def validate_instance(t: Instance, fail: MsgCallback, empty_tuple_index: bool) -> bool:
+def validate_instance(t: Instance, fail: MsgCallback, has_parameters: bool) -> bool:
     """Check if this is a well-formed instance with respect to argument count/positions."""
     # TODO: combine logic with instantiate_type_alias().
     if any(unknown_unpack(a) for a in t.args):
@@ -2485,9 +2485,9 @@ def validate_instance(t: Instance, fail: MsgCallback, empty_tuple_index: bool) -
         ):
             correct = True
         if not t.args:
-            if not (empty_tuple_index and len(t.type.type_vars) == 1):
+            if not (has_parameters and len(t.type.type_vars) == 1):
                 # The Any arguments should be set by the caller.
-                if empty_tuple_index and min_tv_count:
+                if has_parameters and min_tv_count:
                     fail(
                         f"At least {min_tv_count} type argument(s) expected, none given",
                         t,

mypy/types.py

@@ -916,7 +916,7 @@ class UnboundType(ProperType):
         "name",
         "args",
         "optional",
-        "empty_tuple_index",
+        "has_parameters",
         "original_str_expr",
         "original_str_fallback",
     )
@@ -928,7 +928,7 @@ def __init__(
         line: int = -1,
         column: int = -1,
         optional: bool = False,
-        empty_tuple_index: bool = False,
+        has_parameters: bool = False,
         original_str_expr: str | None = None,
         original_str_fallback: str | None = None,
     ) -> None:
@@ -939,8 +939,8 @@ def __init__(
         self.args = tuple(args)
         # Should this type be wrapped in an Optional?
         self.optional = optional
-        # Special case for X[()]
-        self.empty_tuple_index = empty_tuple_index
+        # Distinguish between X[()] and X
+        self.has_parameters = has_parameters
         # If this UnboundType was originally defined as a str or bytes, keep track of
         # the original contents of that string-like thing. This way, if this UnboundExpr
         # ever shows up inside of a LiteralType, we can determine whether that
@@ -966,7 +966,7 @@ def copy_modified(self, args: Bogus[Sequence[Type] | None] = _dummy) -> UnboundT
             line=self.line,
             column=self.column,
             optional=self.optional,
-            empty_tuple_index=self.empty_tuple_index,
+            has_parameters=self.has_parameters,
             original_str_expr=self.original_str_expr,
             original_str_fallback=self.original_str_fallback,
         )

test-data/unit/check-generics.test

@@ -3548,3 +3548,36 @@ def foo(x: T):
     reveal_type(C)  # N: Revealed type is "Overload(def [T, S] (x: builtins.int, y: S`-1) -> __main__.C[__main__.Int[S`-1]], def [T, S] (x: builtins.str, y: S`-1) -> __main__.C[__main__.Str[S`-1]])"
     reveal_type(C(0, x))  # N: Revealed type is "__main__.C[__main__.Int[T`-1]]"
     reveal_type(C("yes", x))  # N: Revealed type is "__main__.C[__main__.Str[T`-1]]"
+
+[case testCanUnpackEmptyTuple]
+# flags: --disallow-any-generics
+from typing import Generic, Unpack, Tuple
+from typing_extensions import TypeVarTuple
+
+Ts = TypeVarTuple("Ts")
+class X(Generic[Unpack[Ts]]): ...
+
+def check(
+    x: X[()],  # works
+    y: X[Unpack[Tuple[()]]],  # works
+    z: X[Unpack[Tuple[Unpack[Tuple[()]]]]],  # works
+): ...
+[builtins fixtures/tuple.pyi]
+
+[case testNoGenericInAlias]
+# flags: --disallow-any-generics
+from typing import Generic, Unpack, Union
+from typing_extensions import TypeVarTuple, TypeAlias
+
+Ts = TypeVarTuple("Ts")
+class X(Generic[Unpack[Ts]]): ...
+
+Alias1 = X
+reveal_type(Alias1)  # N: Revealed type is "def [Ts] () -> __main__.X[Unpack[Ts`1]]"
+
+Alias2 = Union[X]  # E: Missing type parameters for generic type "X[()]"
+reveal_type(Alias2)  # N: Revealed type is "def () -> __main__.X[Unpack[builtins.tuple[Any, ...]]]"
+
+Alias3 = Union[X[()]]
+reveal_type(Alias3)  # N: Revealed type is "def () -> __main__.X[()]"
+[builtins fixtures/tuple.pyi]