Basic ParamSpec Concatenate and literal support (#11847)

This PR adds a new Parameters proper type to represent ParamSpec parameters 
(more about this in the PR), along with supporting the Concatenate operator.

Closes #11833
Closes #12276
Closes #12257
Refs #8645
External ref python/typeshed#4827

Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
Co-authored-by: Marc Mueller <30130371+cdce8p@users.noreply.github.com>

docs/source/config_file.rst

@@ -676,6 +676,13 @@ section of the command line docs.
        from foo import bar
        __all__ = ['bar']
 
+.. confval:: strict_concatenate
+
+    :type: boolean
+    :default: False
+
+    Make arguments prepended via ``Concatenate`` be truly positional-only.
+
 .. confval:: strict_equality
 
     :type: boolean

mypy/applytype.py

@@ -5,7 +5,7 @@
 from mypy.expandtype import expand_type
 from mypy.types import (
     Type, TypeVarId, TypeVarType, CallableType, AnyType, PartialType, get_proper_types,
-    TypeVarLikeType, ProperType, ParamSpecType, get_proper_type
+    TypeVarLikeType, ProperType, ParamSpecType, Parameters, get_proper_type
 )
 from mypy.nodes import Context
 
@@ -94,7 +94,7 @@ def apply_generic_arguments(
         nt = id_to_type.get(param_spec.id)
         if nt is not None:
             nt = get_proper_type(nt)
-            if isinstance(nt, CallableType):
+            if isinstance(nt, CallableType) or isinstance(nt, Parameters):
                 callable = callable.expand_param_spec(nt)
 
     # Apply arguments to argument types.

mypy/checker.py

@@ -5224,7 +5224,7 @@ def check_subtype(self,
                       code: Optional[ErrorCode] = None,
                       outer_context: Optional[Context] = None) -> bool:
         """Generate an error if the subtype is not compatible with supertype."""
-        if is_subtype(subtype, supertype):
+        if is_subtype(subtype, supertype, options=self.options):
             return True
 
         if isinstance(msg, ErrorMessage):
@@ -5260,6 +5260,7 @@ def check_subtype(self,
             self.msg.note(note, context, code=code)
         if note_msg:
             self.note(note_msg, context, code=code)
+        self.msg.maybe_note_concatenate_pos_args(subtype, supertype, context, code=code)
         if (isinstance(supertype, Instance) and supertype.type.is_protocol and
                 isinstance(subtype, (Instance, TupleType, TypedDictType))):
             self.msg.report_protocol_problems(subtype, supertype, context, code=code)

mypy/checkexpr.py

@@ -1556,7 +1556,7 @@ def check_arg(self,
               isinstance(callee_type.item, Instance) and
               (callee_type.item.type.is_abstract or callee_type.item.type.is_protocol)):
             self.msg.concrete_only_call(callee_type, context)
-        elif not is_subtype(caller_type, callee_type):
+        elif not is_subtype(caller_type, callee_type, options=self.chk.options):
             if self.chk.should_suppress_optional_error([caller_type, callee_type]):
                 return
             code = messages.incompatible_argument(n,

mypy/constraints.py

@@ -8,7 +8,7 @@
     TupleType, TypedDictType, UnionType, Overloaded, ErasedType, PartialType, DeletedType,
     UninhabitedType, TypeType, TypeVarId, TypeQuery, is_named_instance, TypeOfAny, LiteralType,
     ProperType, ParamSpecType, get_proper_type, TypeAliasType, is_union_with_any,
-    UnpackType, callable_with_ellipsis, TUPLE_LIKE_INSTANCE_NAMES,
+    UnpackType, callable_with_ellipsis, Parameters, TUPLE_LIKE_INSTANCE_NAMES,
 )
 from mypy.maptype import map_instance_to_supertype
 import mypy.subtypes
@@ -406,6 +406,9 @@ def visit_param_spec(self, template: ParamSpecType) -> List[Constraint]:
     def visit_unpack_type(self, template: UnpackType) -> List[Constraint]:
         raise NotImplementedError
 
+    def visit_parameters(self, template: Parameters) -> List[Constraint]:
+        raise RuntimeError("Parameters cannot be constrained to")
+
     # Non-leaf types
 
     def visit_instance(self, template: Instance) -> List[Constraint]:
@@ -446,7 +449,7 @@ def visit_instance(self, template: Instance) -> List[Constraint]:
                 # N.B: We use zip instead of indexing because the lengths might have
                 # mismatches during daemon reprocessing.
                 for tvar, mapped_arg, instance_arg in zip(tvars, mapped.args, instance.args):
-                    # TODO: ParamSpecType
+                    # TODO(PEP612): More ParamSpec work (or is Parameters the only thing accepted)
                     if isinstance(tvar, TypeVarType):
                         # The constraints for generic type parameters depend on variance.
                         # Include constraints from both directions if invariant.
@@ -456,6 +459,27 @@ def visit_instance(self, template: Instance) -> List[Constraint]:
                         if tvar.variance != COVARIANT:
                             res.extend(infer_constraints(
                                 mapped_arg, instance_arg, neg_op(self.direction)))
+                    elif isinstance(tvar, ParamSpecType) and isinstance(mapped_arg, ParamSpecType):
+                        suffix = get_proper_type(instance_arg)
+
+                        if isinstance(suffix, CallableType):
+                            prefix = mapped_arg.prefix
+                            from_concat = bool(prefix.arg_types) or suffix.from_concatenate
+                            suffix = suffix.copy_modified(from_concatenate=from_concat)
+
+                        if isinstance(suffix, Parameters) or isinstance(suffix, CallableType):
+                            # no such thing as variance for ParamSpecs
+                            # TODO: is there a case I am missing?
+                            # TODO: constraints between prefixes
+                            prefix = mapped_arg.prefix
+                            suffix = suffix.copy_modified(
+                                suffix.arg_types[len(prefix.arg_types):],
+                                suffix.arg_kinds[len(prefix.arg_kinds):],
+                                suffix.arg_names[len(prefix.arg_names):])
+                            res.append(Constraint(mapped_arg.id, SUPERTYPE_OF, suffix))
+                        elif isinstance(suffix, ParamSpecType):
+                            res.append(Constraint(mapped_arg.id, SUPERTYPE_OF, suffix))
+
                 return res
             elif (self.direction == SUPERTYPE_OF and
                     instance.type.has_base(template.type.fullname)):
@@ -464,7 +488,6 @@ def visit_instance(self, template: Instance) -> List[Constraint]:
                 # N.B: We use zip instead of indexing because the lengths might have
                 # mismatches during daemon reprocessing.
                 for tvar, mapped_arg, template_arg in zip(tvars, mapped.args, template.args):
-                    # TODO: ParamSpecType
                     if isinstance(tvar, TypeVarType):
                         # The constraints for generic type parameters depend on variance.
                         # Include constraints from both directions if invariant.
@@ -474,6 +497,28 @@ def visit_instance(self, template: Instance) -> List[Constraint]:
                         if tvar.variance != COVARIANT:
                             res.extend(infer_constraints(
                                 template_arg, mapped_arg, neg_op(self.direction)))
+                    elif (isinstance(tvar, ParamSpecType) and
+                          isinstance(template_arg, ParamSpecType)):
+                        suffix = get_proper_type(mapped_arg)
+
+                        if isinstance(suffix, CallableType):
+                            prefix = template_arg.prefix
+                            from_concat = bool(prefix.arg_types) or suffix.from_concatenate
+                            suffix = suffix.copy_modified(from_concatenate=from_concat)
+
+                        if isinstance(suffix, Parameters) or isinstance(suffix, CallableType):
+                            # no such thing as variance for ParamSpecs
+                            # TODO: is there a case I am missing?
+                            # TODO: constraints between prefixes
+                            prefix = template_arg.prefix
+
+                            suffix = suffix.copy_modified(
+                                suffix.arg_types[len(prefix.arg_types):],
+                                suffix.arg_kinds[len(prefix.arg_kinds):],
+                                suffix.arg_names[len(prefix.arg_names):])
+                            res.append(Constraint(template_arg.id, SUPERTYPE_OF, suffix))
+                        elif isinstance(suffix, ParamSpecType):
+                            res.append(Constraint(template_arg.id, SUPERTYPE_OF, suffix))
                 return res
             if (template.type.is_protocol and self.direction == SUPERTYPE_OF and
                     # We avoid infinite recursion for structural subtypes by checking
@@ -564,11 +609,34 @@ def visit_callable_type(self, template: CallableType) -> List[Constraint]:
                         # Negate direction due to function argument type contravariance.
                         res.extend(infer_constraints(t, a, neg_op(self.direction)))
             else:
+                # sometimes, it appears we try to get constraints between two paramspec callables?
                 # TODO: Direction
-                # TODO: Deal with arguments that come before param spec ones?
-                res.append(Constraint(param_spec.id,
-                                      SUBTYPE_OF,
-                                      cactual.copy_modified(ret_type=NoneType())))
+                # TODO: check the prefixes match
+                prefix = param_spec.prefix
+                prefix_len = len(prefix.arg_types)
+                cactual_ps = cactual.param_spec()
+
+                if not cactual_ps:
+                    res.append(Constraint(param_spec.id,
+                                          SUBTYPE_OF,
+                                          cactual.copy_modified(
+                                            arg_types=cactual.arg_types[prefix_len:],
+                                            arg_kinds=cactual.arg_kinds[prefix_len:],
+                                            arg_names=cactual.arg_names[prefix_len:],
+                                            ret_type=NoneType())))
+                else:
+                    res.append(Constraint(param_spec.id, SUBTYPE_OF, cactual_ps))
+
+                # compare prefixes
+                cactual_prefix = cactual.copy_modified(
+                    arg_types=cactual.arg_types[:prefix_len],
+                    arg_kinds=cactual.arg_kinds[:prefix_len],
+                    arg_names=cactual.arg_names[:prefix_len])
+
+                # TODO: see above "FIX" comments for param_spec is None case
+                # TODO: this assume positional arguments
+                for t, a in zip(prefix.arg_types, cactual_prefix.arg_types):
+                    res.extend(infer_constraints(t, a, neg_op(self.direction)))
 
             template_ret_type, cactual_ret_type = template.ret_type, cactual.ret_type
             if template.type_guard is not None:

mypy/erasetype.py

@@ -4,7 +4,7 @@
     Type, TypeVisitor, UnboundType, AnyType, NoneType, TypeVarId, Instance, TypeVarType,
     CallableType, TupleType, TypedDictType, UnionType, Overloaded, ErasedType, PartialType,
     DeletedType, TypeTranslator, UninhabitedType, TypeType, TypeOfAny, LiteralType, ProperType,
-    get_proper_type, get_proper_types, TypeAliasType, ParamSpecType, UnpackType
+    get_proper_type, get_proper_types, TypeAliasType, ParamSpecType, Parameters, UnpackType
 )
 from mypy.nodes import ARG_STAR, ARG_STAR2
 
@@ -59,6 +59,9 @@ def visit_type_var(self, t: TypeVarType) -> ProperType:
     def visit_param_spec(self, t: ParamSpecType) -> ProperType:
         return AnyType(TypeOfAny.special_form)
 
+    def visit_parameters(self, t: Parameters) -> ProperType:
+        raise RuntimeError("Parameters should have been bound to a class")
+
     def visit_unpack_type(self, t: UnpackType) -> ProperType:
         raise NotImplementedError
 

mypy/expandtype.py

@@ -5,7 +5,8 @@
     NoneType, Overloaded, TupleType, TypedDictType, UnionType,
     ErasedType, PartialType, DeletedType, UninhabitedType, TypeType, TypeVarId,
     FunctionLike, TypeVarType, LiteralType, get_proper_type, ProperType,
-    TypeAliasType, ParamSpecType, TypeVarLikeType, UnpackType
+    TypeAliasType, ParamSpecType, TypeVarLikeType, Parameters, ParamSpecFlavor,
+    UnpackType
 )
 
 
@@ -101,15 +102,41 @@ def visit_param_spec(self, t: ParamSpecType) -> Type:
         repl = get_proper_type(self.variables.get(t.id, t))
         if isinstance(repl, Instance):
             inst = repl
+            # Return copy of instance with type erasure flag on.
+            # TODO: what does prefix mean in this case?
+            # TODO: why does this case even happen? Instances aren't plural.
             return Instance(inst.type, inst.args, line=inst.line, column=inst.column)
         elif isinstance(repl, ParamSpecType):
-            return repl.with_flavor(t.flavor)
+            return repl.copy_modified(flavor=t.flavor, prefix=t.prefix.copy_modified(
+                arg_types=t.prefix.arg_types + repl.prefix.arg_types,
+                arg_kinds=t.prefix.arg_kinds + repl.prefix.arg_kinds,
+                arg_names=t.prefix.arg_names + repl.prefix.arg_names,
+            ))
+        elif isinstance(repl, Parameters) or isinstance(repl, CallableType):
+            # if the paramspec is *P.args or **P.kwargs:
+            if t.flavor != ParamSpecFlavor.BARE:
+                assert isinstance(repl, CallableType), "Should not be able to get here."
+                # Is this always the right thing to do?
+                param_spec = repl.param_spec()
+                if param_spec:
+                    return param_spec.with_flavor(t.flavor)
+                else:
+                    return repl
+            else:
+                return Parameters(t.prefix.arg_types + repl.arg_types,
+                                  t.prefix.arg_kinds + repl.arg_kinds,
+                                  t.prefix.arg_names + repl.arg_names,
+                                  variables=[*t.prefix.variables, *repl.variables])
         else:
+            # TODO: should this branch be removed? better not to fail silently
             return repl
 
     def visit_unpack_type(self, t: UnpackType) -> Type:
         raise NotImplementedError
 
+    def visit_parameters(self, t: Parameters) -> Type:
+        return t.copy_modified(arg_types=self.expand_types(t.arg_types))
+
     def visit_callable_type(self, t: CallableType) -> Type:
         param_spec = t.param_spec()
         if param_spec is not None:
@@ -121,13 +148,18 @@ def visit_callable_type(self, t: CallableType) -> Type:
             # must expand both of them with all the argument types,
             # kinds and names in the replacement. The return type in
             # the replacement is ignored.
-            if isinstance(repl, CallableType):
+            if isinstance(repl, CallableType) or isinstance(repl, Parameters):
                 # Substitute *args: P.args, **kwargs: P.kwargs
-                t = t.expand_param_spec(repl)
-                # TODO: Substitute remaining arg types
-                return t.copy_modified(ret_type=t.ret_type.accept(self),
-                                       type_guard=(t.type_guard.accept(self)
-                                                   if t.type_guard is not None else None))
+                prefix = param_spec.prefix
+                # we need to expand the types in the prefix, so might as well
+                # not get them in the first place
+                t = t.expand_param_spec(repl, no_prefix=True)
+                return t.copy_modified(
+                    arg_types=self.expand_types(prefix.arg_types) + t.arg_types,
+                    arg_kinds=prefix.arg_kinds + t.arg_kinds,
+                    arg_names=prefix.arg_names + t.arg_names,
+                    ret_type=t.ret_type.accept(self),
+                    type_guard=(t.type_guard.accept(self) if t.type_guard is not None else None))
 
         return t.copy_modified(arg_types=self.expand_types(t.arg_types),
                                ret_type=t.ret_type.accept(self),

mypy/fixup.py

@@ -11,7 +11,7 @@
     CallableType, Instance, Overloaded, TupleType, TypedDictType,
     TypeVarType, UnboundType, UnionType, TypeVisitor, LiteralType,
     TypeType, NOT_READY, TypeAliasType, AnyType, TypeOfAny, ParamSpecType,
-    UnpackType,
+    Parameters, UnpackType,
 )
 from mypy.visitor import NodeVisitor
 from mypy.lookup import lookup_fully_qualified
@@ -255,6 +255,11 @@ def visit_param_spec(self, p: ParamSpecType) -> None:
     def visit_unpack_type(self, u: UnpackType) -> None:
         u.type.accept(self)
 
+    def visit_parameters(self, p: Parameters) -> None:
+        for argt in p.arg_types:
+            if argt is not None:
+                argt.accept(self)
+
     def visit_unbound_type(self, o: UnboundType) -> None:
         for a in o.args:
             a.accept(self)

mypy/indirection.py

@@ -70,6 +70,9 @@ def visit_param_spec(self, t: types.ParamSpecType) -> Set[str]:
     def visit_unpack_type(self, t: types.UnpackType) -> Set[str]:
         return t.type.accept(self)
 
+    def visit_parameters(self, t: types.Parameters) -> Set[str]:
+        return self._visit(t.arg_types)
+
     def visit_instance(self, t: types.Instance) -> Set[str]:
         out = self._visit(t.args)
         if t.type:

mypy/join.py

@@ -7,7 +7,7 @@
     Type, AnyType, NoneType, TypeVisitor, Instance, UnboundType, TypeVarType, CallableType,
     TupleType, TypedDictType, ErasedType, UnionType, FunctionLike, Overloaded, LiteralType,
     PartialType, DeletedType, UninhabitedType, TypeType, TypeOfAny, get_proper_type,
-    ProperType, get_proper_types, TypeAliasType, PlaceholderType, ParamSpecType,
+    ProperType, get_proper_types, TypeAliasType, PlaceholderType, ParamSpecType, Parameters,
     UnpackType
 )
 from mypy.maptype import map_instance_to_supertype
@@ -260,6 +260,12 @@ def visit_param_spec(self, t: ParamSpecType) -> ProperType:
     def visit_unpack_type(self, t: UnpackType) -> UnpackType:
         raise NotImplementedError
 
+    def visit_parameters(self, t: Parameters) -> ProperType:
+        if self.s == t:
+            return t
+        else:
+            return self.default(self.s)
+
     def visit_instance(self, t: Instance) -> ProperType:
         if isinstance(self.s, Instance):
             if self.instance_joiner is None:

mypy/main.py

@@ -679,6 +679,10 @@ def add_invertible_flag(flag: str,
                              " non-overlapping types",
                         group=strictness_group)
 
+    add_invertible_flag('--strict-concatenate', default=False, strict_flag=True,
+                        help="Make arguments prepended via Concatenate be truly positional-only",
+                        group=strictness_group)
+
     strict_help = "Strict mode; enables the following flags: {}".format(
         ", ".join(strict_flag_names))
     strictness_group.add_argument(

mypy/meet.py

@@ -6,7 +6,7 @@
     TupleType, TypedDictType, ErasedType, UnionType, PartialType, DeletedType,
     UninhabitedType, TypeType, TypeOfAny, Overloaded, FunctionLike, LiteralType,
     ProperType, get_proper_type, get_proper_types, TypeAliasType, TypeGuardedType,
-    ParamSpecType, UnpackType,
+    ParamSpecType, Parameters, UnpackType,
 )
 from mypy.subtypes import is_equivalent, is_subtype, is_callable_compatible, is_proper_subtype
 from mypy.erasetype import erase_type
@@ -509,6 +509,17 @@ def visit_param_spec(self, t: ParamSpecType) -> ProperType:
     def visit_unpack_type(self, t: UnpackType) -> ProperType:
         raise NotImplementedError
 
+    def visit_parameters(self, t: Parameters) -> ProperType:
+        # TODO: is this the right variance?
+        if isinstance(self.s, Parameters) or isinstance(self.s, CallableType):
+            if len(t.arg_types) != len(self.s.arg_types):
+                return self.default(self.s)
+            return t.copy_modified(
+                arg_types=[meet_types(s_a, t_a) for s_a, t_a in zip(self.s.arg_types, t.arg_types)]
+            )
+        else:
+            return self.default(self.s)
+
     def visit_instance(self, t: Instance) -> ProperType:
         if isinstance(self.s, Instance):
             if t.type == self.s.type: