Give TypeVarTupleType a fallback (#14231)

We want to eventually decomission the use of TypeList for
constraints/expanded values of TypeVarTupleTypes. In order to do that we
will need a reference to the tuple fallback. All the places we currently
construct these TypeLists for the use in variadic generics have access
to a TypeVarTupleType, so putting the tuple fallback into the typevar
type is a reasonable way to make that information accessible where we
need it.

In order to get it into the type, we first put it into the expr by
making a symbol table lookup in semanal.

mypy/copytype.py

@@ -94,7 +94,7 @@ def visit_parameters(self, t: Parameters) -> ProperType:
  return self.copy_common(t, dup)
 
  def visit_type_var_tuple(self, t: TypeVarTupleType) -> ProperType:
- dup = TypeVarTupleType(t.name, t.fullname, t.id, t.upper_bound)
+ dup = TypeVarTupleType(t.name, t.fullname, t.id, t.upper_bound, t.tuple_fallback)
  return self.copy_common(t, dup)
 
  def visit_unpack_type(self, t: UnpackType) -> ProperType:

mypy/nodes.py

@@ -2526,10 +2526,23 @@ def deserialize(cls, data: JsonDict) -> ParamSpecExpr:
 class TypeVarTupleExpr(TypeVarLikeExpr):
  """Type variable tuple expression TypeVarTuple(...)."""
 
- __slots__ = ()
+ __slots__ = "tuple_fallback"
+
+ tuple_fallback: mypy.types.Instance
 
  __match_args__ = ("name", "upper_bound")
 
+ def __init__(
+ self,
+ name: str,
+ fullname: str,
+ upper_bound: mypy.types.Type,
+ tuple_fallback: mypy.types.Instance,
+ variance: int = INVARIANT,
+ ) -> None:
+ super().__init__(name, fullname, upper_bound, variance)
+ self.tuple_fallback = tuple_fallback
+
  def accept(self, visitor: ExpressionVisitor[T]) -> T:
  return visitor.visit_type_var_tuple_expr(self)
 
@@ -2539,6 +2552,7 @@ def serialize(self) -> JsonDict:
  "name": self._name,
  "fullname": self._fullname,
  "upper_bound": self.upper_bound.serialize(),
+ "tuple_fallback": self.tuple_fallback.serialize(),
  "variance": self.variance,
  }
 
@@ -2549,6 +2563,7 @@ def deserialize(cls, data: JsonDict) -> TypeVarTupleExpr:
  data["name"],
  data["fullname"],
  mypy.types.deserialize_type(data["upper_bound"]),
+ mypy.types.Instance.deserialize(data["tuple_fallback"]),
  data["variance"],
  )
 

mypy/semanal.py

@@ -4119,8 +4119,9 @@ def process_typevartuple_declaration(self, s: AssignmentStmt) -> bool:
 
  # PEP 646 does not specify the behavior of variance, constraints, or bounds.
  if not call.analyzed:
+ tuple_fallback = self.named_type("builtins.tuple", [self.object_type()])
  typevartuple_var = TypeVarTupleExpr(
- name, self.qualified_name(name), self.object_type(), INVARIANT
+ name, self.qualified_name(name), self.object_type(), tuple_fallback, INVARIANT
  )
  typevartuple_var.line = call.line
  call.analyzed = typevartuple_var

mypy/test/typefixture.py

@@ -56,9 +56,6 @@ def make_type_var(
  ) -> TypeVarType:
  return TypeVarType(name, name, id, values, upper_bound, variance)
 
- def make_type_var_tuple(name: str, id: int, upper_bound: Type) -> TypeVarTupleType:
- return TypeVarTupleType(name, name, id, upper_bound)
-
  self.t = make_type_var("T", 1, [], self.o, variance) # T`1 (type variable)
  self.tf = make_type_var("T", -1, [], self.o, variance) # T`-1 (type variable)
  self.tf2 = make_type_var("T", -2, [], self.o, variance) # T`-2 (type variable)
@@ -68,10 +65,6 @@ def make_type_var_tuple(name: str, id: int, upper_bound: Type) -> TypeVarTupleTy
  self.sf1 = make_type_var("S", -1, [], self.o, variance) # S`-1 (type variable)
  self.u = make_type_var("U", 3, [], self.o, variance) # U`3 (type variable)
 
- self.ts = make_type_var_tuple("Ts", 1, self.o) # Ts`1 (type var tuple)
- self.ss = make_type_var_tuple("Ss", 2, self.o) # Ss`2 (type var tuple)
- self.us = make_type_var_tuple("Us", 3, self.o) # Us`3 (type var tuple)
-
  # Simple types
  self.anyt = AnyType(TypeOfAny.special_form)
  self.nonet = NoneType()
@@ -133,10 +126,6 @@ def make_type_var_tuple(name: str, id: int, upper_bound: Type) -> TypeVarTupleTy
  bases=[Instance(self.gi, [self.s1])],
  )
 
- self.gvi = self.make_type_info("GV", mro=[self.oi], typevars=["Ts"], typevar_tuple_index=0)
- self.gv2i = self.make_type_info(
- "GV2", mro=[self.oi], typevars=["T", "Ts", "S"], typevar_tuple_index=1
- )
  # list[T]
  self.std_listi = self.make_type_info(
  "builtins.list", mro=[self.oi], typevars=["T"], variances=[variance]
@@ -218,6 +207,18 @@ def make_type_var_tuple(name: str, id: int, upper_bound: Type) -> TypeVarTupleTy
  self._add_bool_dunder(self.bool_type_info)
  self._add_bool_dunder(self.ai)
 
+ def make_type_var_tuple(name: str, id: int, upper_bound: Type) -> TypeVarTupleType:
+ return TypeVarTupleType(name, name, id, upper_bound, self.std_tuple)
+
+ self.ts = make_type_var_tuple("Ts", 1, self.o) # Ts`1 (type var tuple)
+ self.ss = make_type_var_tuple("Ss", 2, self.o) # Ss`2 (type var tuple)
+ self.us = make_type_var_tuple("Us", 3, self.o) # Us`3 (type var tuple)
+
+ self.gvi = self.make_type_info("GV", mro=[self.oi], typevars=["Ts"], typevar_tuple_index=0)
+ self.gv2i = self.make_type_info(
+ "GV2", mro=[self.oi], typevars=["T", "Ts", "S"], typevar_tuple_index=1
+ )
+
  def _add_bool_dunder(self, type_info: TypeInfo) -> None:
  signature = CallableType([], [], [], Instance(self.bool_type_info, []), self.function)
  bool_func = FuncDef("__bool__", [], Block([]))
@@ -296,7 +297,7 @@ def make_type_info(
  v: list[TypeVarLikeType] = []
  for id, n in enumerate(typevars, 1):
  if typevar_tuple_index is not None and id - 1 == typevar_tuple_index:
- v.append(TypeVarTupleType(n, n, id, self.o))
+ v.append(TypeVarTupleType(n, n, id, self.o, self.std_tuple))
  else:
  if variances:
  variance = variances[id - 1]

mypy/treetransform.py

@@ -653,7 +653,11 @@ def visit_paramspec_expr(self, node: ParamSpecExpr) -> ParamSpecExpr:
 
  def visit_type_var_tuple_expr(self, node: TypeVarTupleExpr) -> TypeVarTupleExpr:
  return TypeVarTupleExpr(
- node.name, node.fullname, self.type(node.upper_bound), variance=node.variance
+ node.name,
+ node.fullname,
+ self.type(node.upper_bound),
+ node.tuple_fallback,
+ variance=node.variance,
  )
 
  def visit_type_alias_expr(self, node: TypeAliasExpr) -> TypeAliasExpr:

mypy/tvar_scope.py

@@ -115,6 +115,7 @@ def bind_new(self, name: str, tvar_expr: TypeVarLikeExpr) -> TypeVarLikeType:
  tvar_expr.fullname,
  i,
  upper_bound=tvar_expr.upper_bound,
+ tuple_fallback=tvar_expr.tuple_fallback,
  line=tvar_expr.line,
  column=tvar_expr.column,
  )

mypy/typeanal.py

@@ -364,12 +364,14 @@ def visit_unbound_type_nonoptional(self, t: UnboundType, defining_literal: bool)
  self.fail(
  f'Type variable "{t.name}" used with arguments', t, code=codes.VALID_TYPE
  )
+
  # Change the line number
  return TypeVarTupleType(
  tvar_def.name,
  tvar_def.fullname,
  tvar_def.id,
  tvar_def.upper_bound,
+ sym.node.tuple_fallback,
  line=t.line,
  column=t.column,
  )

mypy/types.py

@@ -720,6 +720,20 @@ class TypeVarTupleType(TypeVarLikeType):
  See PEP646 for more information.
  """
 
+ def __init__(
+ self,
+ name: str,
+ fullname: str,
+ id: TypeVarId | int,
+ upper_bound: Type,
+ tuple_fallback: Instance,
+ *,
+ line: int = -1,
+ column: int = -1,
+ ) -> None:
+ super().__init__(name, fullname, id, upper_bound, line=line, column=column)
+ self.tuple_fallback = tuple_fallback
+
  def serialize(self) -> JsonDict:
  assert not self.id.is_meta_var()
  return {
@@ -728,13 +742,18 @@ def serialize(self) -> JsonDict:
  "fullname": self.fullname,
  "id": self.id.raw_id,
  "upper_bound": self.upper_bound.serialize(),
+ "tuple_fallback": self.tuple_fallback.serialize(),
  }
 
  @classmethod
  def deserialize(cls, data: JsonDict) -> TypeVarTupleType:
  assert data[".class"] == "TypeVarTupleType"
  return TypeVarTupleType(
- data["name"], data["fullname"], data["id"], deserialize_type(data["upper_bound"])
+ data["name"],
+ data["fullname"],
+ data["id"],
+ deserialize_type(data["upper_bound"]),
+ Instance.deserialize(data["tuple_fallback"]),
  )
 
  def accept(self, visitor: TypeVisitor[T]) -> T:
@@ -759,6 +778,7 @@ def copy_modified(self, id: Bogus[TypeVarId | int] = _dummy) -> TypeVarTupleType
  self.fullname,
  self.id if id is _dummy else id,
  self.upper_bound,
+ self.tuple_fallback,
  line=self.line,
  column=self.column,
  )

mypy/typevars.py

@@ -39,7 +39,15 @@ def fill_typevars(typ: TypeInfo) -> Instance | TupleType:
  )
  elif isinstance(tv, TypeVarTupleType):
  tv = UnpackType(
- TypeVarTupleType(tv.name, tv.fullname, tv.id, tv.upper_bound, line=-1, column=-1)
+ TypeVarTupleType(
+ tv.name,
+ tv.fullname,
+ tv.id,
+ tv.upper_bound,
+ tv.tuple_fallback,
+ line=-1,
+ column=-1,
+ )
  )
  else:
  assert isinstance(tv, ParamSpecType)

test-data/unit/semanal-errors.test

@@ -1474,3 +1474,4 @@ y: Unpack[TVariadic] # E: TypeVarTuple "TVariadic" is unbound
 
 class Variadic(Generic[Unpack[TVariadic], Unpack[TVariadic2]]): # E: Can only use one type var tuple in a class def
  pass
+[builtins fixtures/tuple.pyi]

test-data/unit/semanal-types.test

@@ -1560,3 +1560,4 @@ MypyFile:1(
  AssignmentStmt:2(
  NameExpr(TV* [__main__.TV])
  TypeVarTupleExpr:2()))
+[builtins fixtures/tuple.pyi]