Subtyping and inference of user defined variadic types

mypy/erasetype.py

@@ -77,7 +77,16 @@ def visit_deleted_type(self, t: DeletedType) -> ProperType:
         return t
 
     def visit_instance(self, t: Instance) -> ProperType:
-        return Instance(t.type, [AnyType(TypeOfAny.special_form)] * len(t.args), t.line)
+        args: list[Type] = []
+        for tv in t.type.defn.type_vars:
+            # Valid erasure for *Ts is *tuple[Any, ...], not just Any.
+            if isinstance(tv, TypeVarTupleType):
+                args.append(
+                    tv.tuple_fallback.copy_modified(args=[AnyType(TypeOfAny.special_form)])
+                )
+            else:
+                args.append(AnyType(TypeOfAny.special_form))
+        return Instance(t.type, args, t.line)
 
     def visit_type_var(self, t: TypeVarType) -> ProperType:
         return AnyType(TypeOfAny.special_form)

mypy/expandtype.py

@@ -255,7 +255,8 @@ def visit_param_spec(self, t: ParamSpecType) -> Type:
                 variables=[*t.prefix.variables, *repl.variables],
             )
         else:
-            # TODO: replace this with "assert False"
+            # We could encode Any as trivial parameters etc., but it would be too verbose.
+            # TODO: assert this is a trivial type, like Any, Never, or object.
             return repl
 
     def visit_type_var_tuple(self, t: TypeVarTupleType) -> Type:

mypy/fixup.py

@@ -81,11 +81,17 @@ def visit_type_info(self, info: TypeInfo) -> None:
                 info.update_tuple_type(info.tuple_type)
                 if info.special_alias:
                     info.special_alias.alias_tvars = list(info.defn.type_vars)
+                    for i, t in enumerate(info.defn.type_vars):
+                        if isinstance(t, TypeVarTupleType):
+                            info.special_alias.tvar_tuple_index = i
             if info.typeddict_type:
                 info.typeddict_type.accept(self.type_fixer)
                 info.update_typeddict_type(info.typeddict_type)
                 if info.special_alias:
                     info.special_alias.alias_tvars = list(info.defn.type_vars)
+                    for i, t in enumerate(info.defn.type_vars):
+                        if isinstance(t, TypeVarTupleType):
+                            info.special_alias.tvar_tuple_index = i
             if info.declared_metaclass:
                 info.declared_metaclass.accept(self.type_fixer)
             if info.metaclass_type:
@@ -166,11 +172,7 @@ def visit_decorator(self, d: Decorator) -> None:
 
     def visit_class_def(self, c: ClassDef) -> None:
         for v in c.type_vars:
-            if isinstance(v, TypeVarType):
-                for value in v.values:
-                    value.accept(self.type_fixer)
-            v.upper_bound.accept(self.type_fixer)
-            v.default.accept(self.type_fixer)
+            v.accept(self.type_fixer)
 
     def visit_type_var_expr(self, tv: TypeVarExpr) -> None:
         for value in tv.values:
@@ -184,6 +186,7 @@ def visit_paramspec_expr(self, p: ParamSpecExpr) -> None:
 
     def visit_type_var_tuple_expr(self, tv: TypeVarTupleExpr) -> None:
         tv.upper_bound.accept(self.type_fixer)
+        tv.tuple_fallback.accept(self.type_fixer)
         tv.default.accept(self.type_fixer)
 
     def visit_var(self, v: Var) -> None:
@@ -314,6 +317,7 @@ def visit_param_spec(self, p: ParamSpecType) -> None:
         p.default.accept(self)
 
     def visit_type_var_tuple(self, t: TypeVarTupleType) -> None:
+        t.tuple_fallback.accept(self)
         t.upper_bound.accept(self)
         t.default.accept(self)
 
@@ -336,9 +340,6 @@ def visit_union_type(self, ut: UnionType) -> None:
             for it in ut.items:
                 it.accept(self)
 
-    def visit_void(self, o: Any) -> None:
-        pass  # Nothing to descend into.
-
     def visit_type_type(self, t: TypeType) -> None:
         t.item.accept(self)
 

mypy/join.py

@@ -43,8 +43,10 @@
     UninhabitedType,
     UnionType,
     UnpackType,
+    find_unpack_in_list,
     get_proper_type,
     get_proper_types,
+    split_with_prefix_and_suffix,
 )
 
 
@@ -67,7 +69,25 @@ def join_instances(self, t: Instance, s: Instance) -> ProperType:
             args: list[Type] = []
             # N.B: We use zip instead of indexing because the lengths might have
             # mismatches during daemon reprocessing.
-            for ta, sa, type_var in zip(t.args, s.args, t.type.defn.type_vars):
+            if t.type.has_type_var_tuple_type:
+                # We handle joins of variadic instances by simply creating correct mapping
+                # for type arguments and compute the individual joins same as for regular
+                # instances. All the heavy lifting is done in the join of tuple types.
+                assert s.type.type_var_tuple_prefix is not None
+                assert s.type.type_var_tuple_suffix is not None
+                prefix = s.type.type_var_tuple_prefix
+                suffix = s.type.type_var_tuple_suffix
+                tvt = s.type.defn.type_vars[prefix]
+                assert isinstance(tvt, TypeVarTupleType)
+                fallback = tvt.tuple_fallback
+                s_prefix, s_middle, s_suffix = split_with_prefix_and_suffix(s.args, prefix, suffix)
+                t_prefix, t_middle, t_suffix = split_with_prefix_and_suffix(t.args, prefix, suffix)
+                s_args = s_prefix + (TupleType(list(s_middle), fallback),) + s_suffix
+                t_args = t_prefix + (TupleType(list(t_middle), fallback),) + t_suffix
+            else:
+                t_args = t.args
+                s_args = s.args
+            for ta, sa, type_var in zip(t_args, s_args, t.type.defn.type_vars):
                 ta_proper = get_proper_type(ta)
                 sa_proper = get_proper_type(sa)
                 new_type: Type | None = None
@@ -93,6 +113,18 @@ def join_instances(self, t: Instance, s: Instance) -> ProperType:
                         # If the types are different but equivalent, then an Any is involved
                         # so using a join in the contravariant case is also OK.
                         new_type = join_types(ta, sa, self)
+                elif isinstance(type_var, TypeVarTupleType):
+                    new_type = get_proper_type(join_types(ta, sa, self))
+                    # Put the joined arguments back into instance in the normal form:
+                    #   a) Tuple[X, Y, Z] -> [X, Y, Z]
+                    #   b) tuple[X, ...] -> [*tuple[X, ...]]
+                    if isinstance(new_type, Instance):
+                        assert new_type.type.fullname == "builtins.tuple"
+                        new_type = UnpackType(new_type)
+                    else:
+                        assert isinstance(new_type, TupleType)
+                        args.extend(new_type.items)
+                        continue
                 else:
                     # ParamSpec type variables behave the same, independent of variance
                     if not is_equivalent(ta, sa):
@@ -440,6 +472,112 @@ def visit_overloaded(self, t: Overloaded) -> ProperType:
                 return join_types(t, call)
         return join_types(t.fallback, s)
 
+    def join_tuples(self, s: TupleType, t: TupleType) -> list[Type] | None:
+        """Join two tuple types while handling variadic entries.
+
+        This is surprisingly tricky, and we don't handle some tricky corner cases.
+        Most of the trickiness comes from the variadic tuple items like *tuple[X, ...]
+        since they can have arbitrary partial overlaps (while *Ts can't be split).
+        """
+        s_unpack_index = find_unpack_in_list(s.items)
+        t_unpack_index = find_unpack_in_list(t.items)
+        if s_unpack_index is None and t_unpack_index is None:
+            if s.length() == t.length():
+                items: list[Type] = []
+                for i in range(t.length()):
+                    items.append(join_types(t.items[i], s.items[i]))
+                return items
+            return None
+        if s_unpack_index is not None and t_unpack_index is not None:
+            # The most complex case: both tuples have an upack item.
+            s_unpack = s.items[s_unpack_index]
+            assert isinstance(s_unpack, UnpackType)
+            s_unpacked = get_proper_type(s_unpack.type)
+            t_unpack = t.items[t_unpack_index]
+            assert isinstance(t_unpack, UnpackType)
+            t_unpacked = get_proper_type(t_unpack.type)
+            if s.length() == t.length() and s_unpack_index == t_unpack_index:
+                # We can handle a case where arity is perfectly aligned, e.g.
+                # join(Tuple[X1, *tuple[Y1, ...], Z1], Tuple[X2, *tuple[Y2, ...], Z2]).
+                # We can essentially perform the join elementwise.
+                prefix_len = t_unpack_index
+                suffix_len = t.length() - t_unpack_index - 1
+                items = []
+                for si, ti in zip(s.items[:prefix_len], t.items[:prefix_len]):
+                    items.append(join_types(si, ti))
+                joined = join_types(s_unpacked, t_unpacked)
+                if isinstance(joined, TypeVarTupleType):
+                    items.append(UnpackType(joined))
+                elif isinstance(joined, Instance) and joined.type.fullname == "builtins.tuple":
+                    items.append(UnpackType(joined))
+                else:
+                    if isinstance(t_unpacked, Instance):
+                        assert t_unpacked.type.fullname == "builtins.tuple"
+                        tuple_instance = t_unpacked
+                    else:
+                        assert isinstance(t_unpacked, TypeVarTupleType)
+                        tuple_instance = t_unpacked.tuple_fallback
+                    items.append(
+                        UnpackType(
+                            tuple_instance.copy_modified(
+                                args=[object_from_instance(tuple_instance)]
+                            )
+                        )
+                    )
+                if suffix_len:
+                    for si, ti in zip(s.items[-suffix_len:], t.items[-suffix_len:]):
+                        items.append(join_types(si, ti))
+            if s.length() == 1 or t.length() == 1:
+                # Another case we can handle is when one of tuple is purely variadic
+                # (i.e. a non-normalized form of tuple[X, ...]), in this case the join
+                # will be again purely variadic.
+                if not (isinstance(s_unpacked, Instance) and isinstance(t_unpacked, Instance)):
+                    return None
+                assert s_unpacked.type.fullname == "builtins.tuple"
+                assert t_unpacked.type.fullname == "builtins.tuple"
+                mid_joined = join_types(s_unpacked.args[0], t_unpacked.args[0])
+                t_other = [a for i, a in enumerate(t.items) if i != t_unpack_index]
+                s_other = [a for i, a in enumerate(s.items) if i != s_unpack_index]
+                other_joined = join_type_list(s_other + t_other)
+                mid_joined = join_types(mid_joined, other_joined)
+                return [UnpackType(s_unpacked.copy_modified(args=[mid_joined]))]
+            # TODO: are there other case we can handle?
+            return None
+        if s_unpack_index is not None:
+            variadic = s
+            unpack_index = s_unpack_index
+            fixed = t
+        else:
+            assert t_unpack_index is not None
+            variadic = t
+            unpack_index = t_unpack_index
+            fixed = s
+        # Case where one tuple has variadic item and the other one doesn't. The join will
+        # be variadic, since fixed tuple is a subtype of variadic, but not vice versa.
+        unpack = variadic.items[unpack_index]
+        assert isinstance(unpack, UnpackType)
+        unpacked = get_proper_type(unpack.type)
+        if not isinstance(unpacked, Instance):
+            return None
+        if fixed.length() < variadic.length() - 1:
+            # There are no non-trivial types that are supertype of both.
+            return None
+        prefix_len = unpack_index
+        suffix_len = variadic.length() - prefix_len - 1
+        prefix, middle, suffix = split_with_prefix_and_suffix(
+            tuple(fixed.items), prefix_len, suffix_len
+        )
+        items = []
+        for fi, vi in zip(prefix, variadic.items[:prefix_len]):
+            items.append(join_types(fi, vi))
+        mid_joined = join_type_list(list(middle))
+        mid_joined = join_types(mid_joined, unpacked.args[0])
+        items.append(UnpackType(unpacked.copy_modified(args=[mid_joined])))
+        if suffix_len:
+            for fi, vi in zip(suffix, variadic.items[-suffix_len:]):
+                items.append(join_types(fi, vi))
+        return items
+
     def visit_tuple_type(self, t: TupleType) -> ProperType:
         # When given two fixed-length tuples:
         # * If they have the same length, join their subtypes item-wise:
@@ -452,17 +590,15 @@ def visit_tuple_type(self, t: TupleType) -> ProperType:
         #   Tuple[int, bool] + Tuple[bool, ...] becomes Tuple[int, ...]
         # * Joining with any Sequence also returns a Sequence:
         #   Tuple[int, bool] + List[bool] becomes Sequence[int]
-        if isinstance(self.s, TupleType) and self.s.length() == t.length():
+        if isinstance(self.s, TupleType):
             if self.instance_joiner is None:
                 self.instance_joiner = InstanceJoiner()
             fallback = self.instance_joiner.join_instances(
                 mypy.typeops.tuple_fallback(self.s), mypy.typeops.tuple_fallback(t)
             )
             assert isinstance(fallback, Instance)
-            if self.s.length() == t.length():
-                items: list[Type] = []
-                for i in range(t.length()):
-                    items.append(join_types(t.items[i], self.s.items[i]))
+            items = self.join_tuples(self.s, t)
+            if items is not None:
                 return TupleType(items, fallback)
             else:
                 return fallback