Allow Ellipsis in Concatenate; cleanup ParamSpec literals (#15905)

Fixes #14761
Fixes #15318
Fixes #14656
Fixes #13518

I noticed there is a bunch of inconsistencies in `semanal`/`typeanal`
for ParamSpecs, so I decided do a small cleanup. Using this opportunity
I also allow `Concatenate[int, ...]` (with literal Ellipsis), and reduce
verbosity of some errors.

cc @A5rocks

mypy/semanal.py

@@ -5285,20 +5285,18 @@ def analyze_type_application_args(self, expr: IndexExpr) -> list[Type] | None:
         else:
             items = [index]
 
-        # whether param spec literals be allowed here
-        # TODO: should this be computed once and passed in?
-        #   or is there a better way to do this?
+        # TODO: this needs a clean-up.
+        # Probably always allow Parameters literals, and validate in semanal_typeargs.py
         base = expr.base
         if isinstance(base, RefExpr) and isinstance(base.node, TypeAlias):
             alias = base.node
-            target = get_proper_type(alias.target)
-            if isinstance(target, Instance):
-                has_param_spec = target.type.has_param_spec_type
-                num_args = len(target.type.type_vars)
+            if any(isinstance(t, ParamSpecType) for t in alias.alias_tvars):
+                has_param_spec = True
+                num_args = len(alias.alias_tvars)
             else:
                 has_param_spec = False
                 num_args = -1
-        elif isinstance(base, NameExpr) and isinstance(base.node, TypeInfo):
+        elif isinstance(base, RefExpr) and isinstance(base.node, TypeInfo):
             has_param_spec = base.node.has_param_spec_type
             num_args = len(base.node.type_vars)
         else:

mypy/typeanal.py

@@ -226,6 +226,8 @@ def __init__(
         self.allow_required = allow_required
         # Are we in a context where ParamSpec literals are allowed?
         self.allow_param_spec_literals = allow_param_spec_literals
+        # Are we in context where literal "..." specifically is allowed?
+        self.allow_ellipsis = False
         # Should we report an error whenever we encounter a RawExpressionType outside
         # of a Literal context: e.g. whenever we encounter an invalid type? Normally,
         # we want to report an error, but the caller may want to do more specialized
@@ -461,9 +463,9 @@ def apply_concatenate_operator(self, t: UnboundType) -> Type:
             self.api.fail("Concatenate needs type arguments", t, code=codes.VALID_TYPE)
             return AnyType(TypeOfAny.from_error)
 
-        # last argument has to be ParamSpec
-        ps = self.anal_type(t.args[-1], allow_param_spec=True)
-        if not isinstance(ps, ParamSpecType):
+        # Last argument has to be ParamSpec or Ellipsis.
+        ps = self.anal_type(t.args[-1], allow_param_spec=True, allow_ellipsis=True)
+        if not isinstance(ps, (ParamSpecType, Parameters)):
             if isinstance(ps, UnboundType) and self.allow_unbound_tvars:
                 sym = self.lookup_qualified(ps.name, t)
                 if sym is not None and isinstance(sym.node, ParamSpecExpr):
@@ -477,19 +479,19 @@ def apply_concatenate_operator(self, t: UnboundType) -> Type:
 
         # TODO: this may not work well with aliases, if those worked.
         #   Those should be special-cased.
-        elif ps.prefix.arg_types:
+        elif isinstance(ps, ParamSpecType) and ps.prefix.arg_types:
             self.api.fail("Nested Concatenates are invalid", t, code=codes.VALID_TYPE)
 
         args = self.anal_array(t.args[:-1])
-        pre = ps.prefix
+        pre = ps.prefix if isinstance(ps, ParamSpecType) else ps
 
         # mypy can't infer this :(
         names: list[str | None] = [None] * len(args)
 
         pre = Parameters(
             args + pre.arg_types, [ARG_POS] * len(args) + pre.arg_kinds, names + pre.arg_names
         )
-        return ps.copy_modified(prefix=pre)
+        return ps.copy_modified(prefix=pre) if isinstance(ps, ParamSpecType) else pre
 
     def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Type | None:
         """Bind special type that is recognized through magic name such as 'typing.Any'.
@@ -880,7 +882,7 @@ def visit_deleted_type(self, t: DeletedType) -> Type:
         return t
 
     def visit_type_list(self, t: TypeList) -> Type:
-        # paramspec literal (Z[[int, str, Whatever]])
+        # Parameters literal (Z[[int, str, Whatever]])
         if self.allow_param_spec_literals:
             params = self.analyze_callable_args(t)
             if params:
@@ -893,7 +895,8 @@ def visit_type_list(self, t: TypeList) -> Type:
             self.fail(
                 'Bracketed expression "[...]" is not valid as a type', t, code=codes.VALID_TYPE
             )
-            self.note('Did you mean "List[...]"?', t)
+            if len(t.items) == 1:
+                self.note('Did you mean "List[...]"?', t)
             return AnyType(TypeOfAny.from_error)
 
     def visit_callable_argument(self, t: CallableArgument) -> Type:
@@ -1106,7 +1109,7 @@ def visit_partial_type(self, t: PartialType) -> Type:
         assert False, "Internal error: Unexpected partial type"
 
     def visit_ellipsis_type(self, t: EllipsisType) -> Type:
-        if self.allow_param_spec_literals:
+        if self.allow_ellipsis or self.allow_param_spec_literals:
             any_type = AnyType(TypeOfAny.explicit)
             return Parameters(
                 [any_type, any_type], [ARG_STAR, ARG_STAR2], [None, None], is_ellipsis_args=True
@@ -1174,7 +1177,7 @@ def analyze_callable_args_for_paramspec(
 
     def analyze_callable_args_for_concatenate(
         self, callable_args: Type, ret_type: Type, fallback: Instance
-    ) -> CallableType | None:
+    ) -> CallableType | AnyType | None:
         """Construct a 'Callable[C, RET]', where C is Concatenate[..., P], returning None if we
         cannot.
         """
@@ -1189,7 +1192,7 @@ def analyze_callable_args_for_concatenate(
             return None
 
         tvar_def = self.anal_type(callable_args, allow_param_spec=True)
-        if not isinstance(tvar_def, ParamSpecType):
+        if not isinstance(tvar_def, (ParamSpecType, Parameters)):
             if self.allow_unbound_tvars and isinstance(tvar_def, UnboundType):
                 sym = self.lookup_qualified(tvar_def.name, callable_args)
                 if sym is not None and isinstance(sym.node, ParamSpecExpr):
@@ -1198,7 +1201,18 @@ def analyze_callable_args_for_concatenate(
                     return callable_with_ellipsis(
                         AnyType(TypeOfAny.explicit), ret_type=ret_type, fallback=fallback
                     )
-            return None
+            # Error was already given, so prevent further errors.
+            return AnyType(TypeOfAny.from_error)
+        if isinstance(tvar_def, Parameters):
+            # This comes from Concatenate[int, ...]
+            return CallableType(
+                arg_types=tvar_def.arg_types,
+                arg_names=tvar_def.arg_names,
+                arg_kinds=tvar_def.arg_kinds,
+                ret_type=ret_type,
+                fallback=fallback,
+                from_concatenate=True,
+            )
 
         # ick, CallableType should take ParamSpecType
         prefix = tvar_def.prefix
@@ -1257,7 +1271,7 @@ def analyze_callable_type(self, t: UnboundType) -> Type:
                     ) or self.analyze_callable_args_for_concatenate(
                         callable_args, ret_type, fallback
                     )
-                    if maybe_ret:
+                    if isinstance(maybe_ret, CallableType):
                         maybe_ret = maybe_ret.copy_modified(
                             ret_type=ret_type.accept(self), variables=variables
                         )
@@ -1274,6 +1288,8 @@ def analyze_callable_type(self, t: UnboundType) -> Type:
                         t,
                     )
                     return AnyType(TypeOfAny.from_error)
+                elif isinstance(maybe_ret, AnyType):
+                    return maybe_ret
                 ret = maybe_ret
         else:
             if self.options.disallow_any_generics:
@@ -1527,17 +1543,27 @@ def anal_array(
         self.allow_param_spec_literals = old_allow_param_spec_literals
         return self.check_unpacks_in_list(res)
 
-    def anal_type(self, t: Type, nested: bool = True, *, allow_param_spec: bool = False) -> Type:
+    def anal_type(
+        self,
+        t: Type,
+        nested: bool = True,
+        *,
+        allow_param_spec: bool = False,
+        allow_ellipsis: bool = False,
+    ) -> Type:
         if nested:
             self.nesting_level += 1
         old_allow_required = self.allow_required
         self.allow_required = False
+        old_allow_ellipsis = self.allow_ellipsis
+        self.allow_ellipsis = allow_ellipsis
         try:
             analyzed = t.accept(self)
         finally:
             if nested:
                 self.nesting_level -= 1
             self.allow_required = old_allow_required
+            self.allow_ellipsis = old_allow_ellipsis
         if (
             not allow_param_spec
             and isinstance(analyzed, ParamSpecType)

test-data/unit/check-literal.test

@@ -611,8 +611,7 @@ from typing_extensions import Literal
 a: (1, 2, 3)                    # E: Syntax error in type annotation \
                                 # N: Suggestion: Use Tuple[T1, ..., Tn] instead of (T1, ..., Tn)
 b: Literal[[1, 2, 3]]           # E: Parameter 1 of Literal[...] is invalid
-c: [1, 2, 3]                    # E: Bracketed expression "[...]" is not valid as a type \
-                                # N: Did you mean "List[...]"?
+c: [1, 2, 3]                    # E: Bracketed expression "[...]" is not valid as a type
 [builtins fixtures/tuple.pyi]
 [out]
 

test-data/unit/check-parameter-specification.test

@@ -38,6 +38,74 @@ def foo6(x: Callable[[P], int]) -> None: ...  # E: Invalid location for ParamSpe
                                               # N: You can use ParamSpec as the first argument to Callable, e.g., 'Callable[P, int]'
 [builtins fixtures/paramspec.pyi]
 
+[case testParamSpecImports]
+import lib
+from lib import Base
+
+class C(Base[[int]]):
+    def test(self, x: int): ...
+
+class D(lib.Base[[int]]):
+    def test(self, x: int): ...
+
+class E(lib.Base[...]): ...
+reveal_type(E().test)  # N: Revealed type is "def (*Any, **Any)"
+
+[file lib.py]
+from typing import Generic
+from typing_extensions import ParamSpec
+
+P = ParamSpec("P")
+class Base(Generic[P]):
+    def test(self, *args: P.args, **kwargs: P.kwargs) -> None:
+        ...
+[builtins fixtures/paramspec.pyi]
+
+[case testParamSpecEllipsisInAliases]
+from typing import Any, Callable, Generic, TypeVar
+from typing_extensions import ParamSpec
+
+P = ParamSpec('P')
+R = TypeVar('R')
+Alias = Callable[P, R]
+
+class B(Generic[P]): ...
+Other = B[P]
+
+T = TypeVar('T', bound=Alias[..., Any])
+Alias[..., Any]  # E: Type application is only supported for generic classes
+B[...]
+Other[...]
+[builtins fixtures/paramspec.pyi]
+
+[case testParamSpecEllipsisInConcatenate]
+from typing import Any, Callable, Generic, TypeVar
+from typing_extensions import ParamSpec, Concatenate
+
+P = ParamSpec('P')
+R = TypeVar('R')
+Alias = Callable[P, R]
+
+IntFun = Callable[Concatenate[int, ...], None]
+f: IntFun
+reveal_type(f)  # N: Revealed type is "def (builtins.int, *Any, **Any)"
+
+g: Callable[Concatenate[int, ...], None]
+reveal_type(g)  # N: Revealed type is "def (builtins.int, *Any, **Any)"
+
+class B(Generic[P]):
+    def test(self, *args: P.args, **kwargs: P.kwargs) -> None:
+        ...
+
+x: B[Concatenate[int, ...]]
+reveal_type(x.test)  # N: Revealed type is "def (builtins.int, *Any, **Any)"
+
+Bad = Callable[Concatenate[int, [int, str]], None]  # E: The last parameter to Concatenate needs to be a ParamSpec \
+                                                    # E: Bracketed expression "[...]" is not valid as a type
+def bad(fn: Callable[Concatenate[P, int], None]):  # E: The last parameter to Concatenate needs to be a ParamSpec
+    ...
+[builtins fixtures/paramspec.pyi]
+
 [case testParamSpecContextManagerLike]
 from typing import Callable, List, Iterator, TypeVar
 from typing_extensions import ParamSpec
@@ -1431,8 +1499,7 @@ from typing import ParamSpec, Generic, List, TypeVar, Callable
 P = ParamSpec("P")
 T = TypeVar("T")
 A = List[T]
-def f(x: A[[int, str]]) -> None: ...  # E: Bracketed expression "[...]" is not valid as a type \
-                                      # N: Did you mean "List[...]"?
+def f(x: A[[int, str]]) -> None: ...  # E: Bracketed expression "[...]" is not valid as a type
 def g(x: A[P]) -> None: ...  # E: Invalid location for ParamSpec "P" \
                              # N: You can use ParamSpec as the first argument to Callable, e.g., 'Callable[P, int]'
 

test-data/unit/check-typevar-defaults.test

@@ -59,9 +59,9 @@ from typing import TypeVar, ParamSpec, Tuple
 from typing_extensions import TypeVarTuple, Unpack
 
 T1 = TypeVar("T1", default=2)  # E: TypeVar "default" must be a type
-T2 = TypeVar("T2", default=[int, str])  # E: Bracketed expression "[...]" is not valid as a type \
-                                        # N: Did you mean "List[...]"? \
-                                        # E: TypeVar "default" must be a type
+T2 = TypeVar("T2", default=[int])  # E: Bracketed expression "[...]" is not valid as a type \
+                                   # N: Did you mean "List[...]"? \
+                                   # E: TypeVar "default" must be a type
 
 P1 = ParamSpec("P1", default=int)  # E: The default argument to ParamSpec must be a list expression, ellipsis, or a ParamSpec
 P2 = ParamSpec("P2", default=2)  # E: The default argument to ParamSpec must be a list expression, ellipsis, or a ParamSpec

test-data/unit/semanal-errors.test

@@ -810,8 +810,8 @@ class C(Generic[t]): pass
 cast(str + str, None)    # E: Cast target is not a type
 cast(C[str][str], None)  # E: Cast target is not a type
 cast(C[str + str], None) # E: Cast target is not a type
-cast([int, str], None)   # E: Bracketed expression "[...]" is not valid as a type \
-                         # N: Did you mean "List[...]"?
+cast([int], None)   # E: Bracketed expression "[...]" is not valid as a type \
+                    # N: Did you mean "List[...]"?
 [out]
 
 [case testInvalidCastTargetType]
@@ -859,8 +859,8 @@ Any(arg=str)  # E: Any(...) is no longer supported. Use cast(Any, ...) instead
 
 [case testTypeListAsType]
 
-def f(x:[int, str]) -> None: # E: Bracketed expression "[...]" is not valid as a type \
-                             # N: Did you mean "List[...]"?
+def f(x: [int]) -> None: # E: Bracketed expression "[...]" is not valid as a type \
+                         # N: Did you mean "List[...]"?
     pass
 [out]