Fix disallow-any errors for Instance types (PEP 696) (#16832)

Similar to TypeAlias types `Missing type parameters for generic type`
should not be emitted if too many arguments are given. There is a
separate error message for that.

Ref: #14851

Author: cdce8p

mypy/messages.py

@@ -2515,10 +2515,10 @@ def format_literal_value(typ: LiteralType) -> str:
         else:
             base_str = itype.type.name
         if not itype.args:
-            if not itype.type.has_type_var_tuple_type:
-                # No type arguments, just return the type name
-                return base_str
-            return base_str + "[()]"
+            if itype.type.has_type_var_tuple_type and len(itype.type.type_vars) == 1:
+                return base_str + "[()]"
+            # No type arguments, just return the type name
+            return base_str
         elif itype.type.fullname == "builtins.tuple":
             item_type_str = format(itype.args[0])
             return f"{'tuple' if options.use_lowercase_names() else 'Tuple'}[{item_type_str}, ...]"

mypy/typeanal.py

@@ -1866,7 +1866,11 @@ def fix_instance(
     max_tv_count = len(t.type.type_vars)
     if arg_count < min_tv_count or arg_count > max_tv_count:
         # Don't use existing args if arg_count doesn't match
+        if arg_count > max_tv_count:
+            # Already wrong arg count error, don't emit missing type parameters error as well.
+            disallow_any = False
         t.args = ()
+        arg_count = 0
 
     args: list[Type] = [*(t.args[:max_tv_count])]
     any_type: AnyType | None = None
@@ -2324,7 +2328,6 @@ def validate_instance(t: Instance, fail: MsgCallback, empty_tuple_index: bool) -
                 t,
                 code=codes.TYPE_ARG,
             )
-            t.args = ()
             t.invalid = True
         return False
     return True

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

@@ -118,6 +118,7 @@ def func_c1(x: Union[int, Callable[[Unpack[Ts1]], None]]) -> Tuple[Unpack[Ts1]]:
 [builtins fixtures/tuple.pyi]
 
 [case testTypeVarDefaultsClass1]
+# flags: --disallow-any-generics
 from typing import Generic, TypeVar, Union, overload
 
 T1 = TypeVar("T1")
@@ -149,7 +150,7 @@ def func_a1(
 class ClassA2(Generic[T1, T2, T3]): ...
 
 def func_a2(
-    a: ClassA2,
+    a: ClassA2,  # E: Missing type parameters for generic type "ClassA2"
     b: ClassA2[float],
     c: ClassA2[float, float],
     d: ClassA2[float, float, float],
@@ -180,7 +181,7 @@ class ClassA3(Generic[T1, T2]):
     def __init__(self, var: Union[int, None] = None) -> None: ...
 
 def func_a3(
-    a: ClassA3,
+    a: ClassA3,  # E: Missing type parameters for generic type "ClassA3"
     b: ClassA3[float],
     c: ClassA3[float, float],
     d: ClassA3[float, float, float],  # E: "ClassA3" expects between 1 and 2 type arguments, but 3 given
@@ -200,6 +201,7 @@ def func_a3(
     reveal_type(n)  # N: Revealed type is "Any"
 
 [case testTypeVarDefaultsClass2]
+# flags: --disallow-any-generics
 from typing import Generic, ParamSpec
 
 P1 = ParamSpec("P1")
@@ -231,7 +233,7 @@ def func_b1(
 class ClassB2(Generic[P1, P2]): ...
 
 def func_b2(
-    a: ClassB2,
+    a: ClassB2,  # E: Missing type parameters for generic type "ClassB2"
     b: ClassB2[[float]],
     c: ClassB2[[float], [float]],
     d: ClassB2[[float], [float], [float]],  # E: "ClassB2" expects between 1 and 2 type arguments, but 3 given
@@ -251,6 +253,7 @@ def func_b2(
     reveal_type(n)  # N: Revealed type is "Any"
 
 [case testTypeVarDefaultsClass3]
+# flags: --disallow-any-generics
 from typing import Generic, Tuple, TypeVar
 from typing_extensions import TypeVarTuple, Unpack
 
@@ -315,7 +318,7 @@ def func_c3(
 class ClassC4(Generic[T1, Unpack[Ts1], T3]): ...
 
 def func_c4(
-    a: ClassC4,
+    a: ClassC4,  # E: Missing type parameters for generic type "ClassC4"
     b: ClassC4[int],
     c: ClassC4[int, float],
 ) -> None: