gh-99344, gh-99379, gh-99382: Fix issues in substitution of ParamSpec and TypeVarTuple (GH-99412)

* Fix substitution of TypeVarTuple and ParamSpec together in user generics.

* Fix substitution of ParamSpec followed by TypeVarTuple in generic aliases.

* Check the number of arguments in substitution in user generics containing a
  TypeVarTuple and one or more TypeVar.
(cherry picked from commit 8f2fb7dfe72c882e97e524ef7ce40ceb663cc27e)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

2 files changed, 111 insertions, 41 deletions

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 1206ab7..efa4cb3 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -769,20 +769,42 @@ class GenericAliasSubstitutionTests(BaseTestCase):
             ('generic[*Ts]',                           '[*Ts]',                                          'generic[*Ts]'),
             ('generic[*Ts]',                           '[T, *Ts]',                                       'generic[T, *Ts]'),
             ('generic[*Ts]',                           '[*Ts, T]',                                       'generic[*Ts, T]'),
+            ('generic[T, *Ts]',                        '[()]',                                           'TypeError'),
             ('generic[T, *Ts]',                        '[int]',                                          'generic[int]'),
             ('generic[T, *Ts]',                        '[int, str]',                                     'generic[int, str]'),
             ('generic[T, *Ts]',                        '[int, str, bool]',                               'generic[int, str, bool]'),
+            ('generic[list[T], *Ts]',                  '[()]',                                           'TypeError'),
             ('generic[list[T], *Ts]',                  '[int]',                                          'generic[list[int]]'),
             ('generic[list[T], *Ts]',                  '[int, str]',                                     'generic[list[int], str]'),
             ('generic[list[T], *Ts]',                  '[int, str, bool]',                               'generic[list[int], str, bool]'),
 
+            ('generic[*Ts, T]',                        '[()]',                                           'TypeError'),
             ('generic[*Ts, T]',                        '[int]',                                          'generic[int]'),
             ('generic[*Ts, T]',                        '[int, str]',                                     'generic[int, str]'),
             ('generic[*Ts, T]',                        '[int, str, bool]',                               'generic[int, str, bool]'),
+            ('generic[*Ts, list[T]]',                  '[()]',                                           'TypeError'),
             ('generic[*Ts, list[T]]',                  '[int]',                                          'generic[list[int]]'),
             ('generic[*Ts, list[T]]',                  '[int, str]',                                     'generic[int, list[str]]'),
             ('generic[*Ts, list[T]]',                  '[int, str, bool]',                               'generic[int, str, list[bool]]'),
 
+            ('generic[T1, T2, *Ts]',                   '[()]',                                           'TypeError'),
+            ('generic[T1, T2, *Ts]',                   '[int]',                                          'TypeError'),
+            ('generic[T1, T2, *Ts]',                   '[int, str]',                                     'generic[int, str]'),
+            ('generic[T1, T2, *Ts]',                   '[int, str, bool]',                               'generic[int, str, bool]'),
+            ('generic[T1, T2, *Ts]',                   '[int, str, bool, bytes]',                        'generic[int, str, bool, bytes]'),
+
+            ('generic[*Ts, T1, T2]',                   '[()]',                                           'TypeError'),
+            ('generic[*Ts, T1, T2]',                   '[int]',                                          'TypeError'),
+            ('generic[*Ts, T1, T2]',                   '[int, str]',                                     'generic[int, str]'),
+            ('generic[*Ts, T1, T2]',                   '[int, str, bool]',                               'generic[int, str, bool]'),
+            ('generic[*Ts, T1, T2]',                   '[int, str, bool, bytes]',                        'generic[int, str, bool, bytes]'),
+
+            ('generic[T1, *Ts, T2]',                   '[()]',                                           'TypeError'),
+            ('generic[T1, *Ts, T2]',                   '[int]',                                          'TypeError'),
+            ('generic[T1, *Ts, T2]',                   '[int, str]',                                     'generic[int, str]'),
+            ('generic[T1, *Ts, T2]',                   '[int, str, bool]',                               'generic[int, str, bool]'),
+            ('generic[T1, *Ts, T2]',                   '[int, str, bool, bytes]',                        'generic[int, str, bool, bytes]'),
+
             ('generic[T, *Ts]',                        '[*tuple_type[int, ...]]',                        'generic[int, *tuple_type[int, ...]]'),
             ('generic[T, *Ts]',                        '[str, *tuple_type[int, ...]]',                   'generic[str, *tuple_type[int, ...]]'),
             ('generic[T, *Ts]',                        '[*tuple_type[int, ...], str]',                   'generic[int, *tuple_type[int, ...], str]'),
@@ -7190,6 +7212,65 @@ class ParamSpecTests(BaseTestCase):
         self.assertEqual(G1.__args__, ((int, str), (bytes,)))
         self.assertEqual(G2.__args__, ((int,), (str, bytes)))
 
+    def test_typevartuple_and_paramspecs_in_user_generics(self):
+        Ts = TypeVarTuple("Ts")
+        P = ParamSpec("P")
+
+        class X(Generic[*Ts, P]):
+            f: Callable[P, int]
+            g: Tuple[*Ts]
+
+        G1 = X[int, [bytes]]
+        self.assertEqual(G1.__args__, (int, (bytes,)))
+        G2 = X[int, str, [bytes]]
+        self.assertEqual(G2.__args__, (int, str, (bytes,)))
+        G3 = X[[bytes]]
+        self.assertEqual(G3.__args__, ((bytes,),))
+        G4 = X[[]]
+        self.assertEqual(G4.__args__, ((),))
+        with self.assertRaises(TypeError):
+            X[()]
+
+        class Y(Generic[P, *Ts]):
+            f: Callable[P, int]
+            g: Tuple[*Ts]
+
+        G1 = Y[[bytes], int]
+        self.assertEqual(G1.__args__, ((bytes,), int))
+        G2 = Y[[bytes], int, str]
+        self.assertEqual(G2.__args__, ((bytes,), int, str))
+        G3 = Y[[bytes]]
+        self.assertEqual(G3.__args__, ((bytes,),))
+        G4 = Y[[]]
+        self.assertEqual(G4.__args__, ((),))
+        with self.assertRaises(TypeError):
+            Y[()]
+
+    def test_typevartuple_and_paramspecs_in_generic_aliases(self):
+        P = ParamSpec('P')
+        T = TypeVar('T')
+        Ts = TypeVarTuple('Ts')
+
+        for C in Callable, collections.abc.Callable:
+            with self.subTest(generic=C):
+                A = C[P, Tuple[*Ts]]
+                B = A[[int, str], bytes, float]
+                self.assertEqual(B.__args__, (int, str, Tuple[bytes, float]))
+
+        class X(Generic[T, P]):
+            pass
+
+        A = X[Tuple[*Ts], P]
+        B = A[bytes, float, [int, str]]
+        self.assertEqual(B.__args__, (Tuple[bytes, float], (int, str,)))
+
+        class Y(Generic[P, T]):
+            pass
+
+        A = Y[P, Tuple[*Ts]]
+        B = A[[int, str], bytes, float]
+        self.assertEqual(B.__args__, ((int, str,), Tuple[bytes, float]))
+
     def test_var_substitution(self):
         T = TypeVar("T")
         P = ParamSpec("P")
diff --git a/Lib/typing.py b/Lib/typing.py
index 9c4d653..9818237 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -284,25 +284,6 @@ def _unpack_args(args):
             newargs.append(arg)
     return newargs
 
-def _prepare_paramspec_params(cls, params):
-    """Prepares the parameters for a Generic containing ParamSpec
-    variables (internal helper).
-    """
-    # Special case where Z[[int, str, bool]] == Z[int, str, bool] in PEP 612.
-    if (len(cls.__parameters__) == 1
-            and params and not _is_param_expr(params[0])):
-        assert isinstance(cls.__parameters__[0], ParamSpec)
-        return (params,)
-    else:
-        _check_generic(cls, params, len(cls.__parameters__))
-        _params = []
-        # Convert lists to tuples to help other libraries cache the results.
-        for p, tvar in zip(params, cls.__parameters__):
-            if isinstance(tvar, ParamSpec) and isinstance(p, list):
-                p = tuple(p)
-            _params.append(p)
-        return tuple(_params)
-
 def _deduplicate(params):
     # Weed out strict duplicates, preserving the first of each occurrence.
     all_params = set(params)
@@ -1226,7 +1207,18 @@ class ParamSpec(_Final, _Immutable, _BoundVarianceMixin, _PickleUsingNameMixin,
         return arg
 
     def __typing_prepare_subst__(self, alias, args):
-        return _prepare_paramspec_params(alias, args)
+        params = alias.__parameters__
+        i = params.index(self)
+        if i >= len(args):
+            raise TypeError(f"Too few arguments for {alias}")
+        # Special case where Z[[int, str, bool]] == Z[int, str, bool] in PEP 612.
+        if len(params) == 1 and not _is_param_expr(args[0]):
+            assert i == 0
+            args = (args,)
+        # Convert lists to tuples to help other libraries cache the results.
+        elif isinstance(args[i], list):
+            args = (*args[:i], tuple(args[i]), *args[i+1:])
+        return args
 
 def _is_dunder(attr):
     return attr.startswith('__') and attr.endswith('__')
@@ -1789,23 +1781,13 @@ class Generic:
         if not isinstance(params, tuple):
             params = (params,)
 
-        if not params:
-            # We're only ok with `params` being empty if the class's only type
-            # parameter is a `TypeVarTuple` (which can contain zero types).
-            class_params = getattr(cls, "__parameters__", None)
-            only_class_parameter_is_typevartuple = (
-                    class_params is not None
-                    and len(class_params) == 1
-                    and isinstance(class_params[0], TypeVarTuple)
-            )
-            if not only_class_parameter_is_typevartuple:
-                raise TypeError(
-                    f"Parameter list to {cls.__qualname__}[...] cannot be empty"
-                )
-
         params = tuple(_type_convert(p) for p in params)
         if cls in (Generic, Protocol):
             # Generic and Protocol can only be subscripted with unique type variables.
+            if not params:
+                raise TypeError(
+                    f"Parameter list to {cls.__qualname__}[...] cannot be empty"
+                )
             if not all(_is_typevar_like(p) for p in params):
                 raise TypeError(
                     f"Parameters to {cls.__name__}[...] must all be type variables "
@@ -1815,13 +1797,20 @@ class Generic:
                     f"Parameters to {cls.__name__}[...] must all be unique")
         else:
             # Subscripting a regular Generic subclass.
-            if any(isinstance(t, ParamSpec) for t in cls.__parameters__):
-                params = _prepare_paramspec_params(cls, params)
-            elif not any(isinstance(p, TypeVarTuple) for p in cls.__parameters__):
-                # We only run this if there are no TypeVarTuples, because we
-                # don't check variadic generic arity at runtime (to reduce
-                # complexity of typing.py).
-                _check_generic(cls, params, len(cls.__parameters__))
+            for param in cls.__parameters__:
+                prepare = getattr(param, '__typing_prepare_subst__', None)
+                if prepare is not None:
+                    params = prepare(cls, params)
+            _check_generic(cls, params, len(cls.__parameters__))
+
+            new_args = []
+            for param, new_arg in zip(cls.__parameters__, params):
+                if isinstance(param, TypeVarTuple):
+                    new_args.extend(new_arg)
+                else:
+                    new_args.append(new_arg)
+            params = tuple(new_args)
+
         return _GenericAlias(cls, params,
                              _paramspec_tvars=True)