Fix error message for type application on non-generic expressions

achbj · claude · achbj · commit 5a11fee2aa9a · 2026-04-23T11:12:34.000+02:00
Update the error message "Type application is only supported for generic classes" to also mention type aliases, since type application is also valid for generic type aliases. Fixes #20927. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
diff --git a/mypy/message_registry.py b/mypy/message_registry.py
@@ -121,7 +121,7 @@ def with_additional_msg(self, info: str) -> ErrorMessage:
     "Function is missing a type annotation", codes.NO_UNTYPED_DEF
 )
 ONLY_CLASS_APPLICATION: Final = ErrorMessage(
-    "Type application is only supported for generic classes"
+    "Type application is only supported for generic classes and type aliases"
 )
 RETURN_TYPE_EXPECTED: Final = ErrorMessage(
     "Function is missing a return type annotation", codes.NO_UNTYPED_DEF
diff --git a/test-data/unit/check-generics.test b/test-data/unit/check-generics.test
@@ -426,7 +426,7 @@ from typing import TypeVar
 T = TypeVar('T')
 def f(x: T) -> T: pass
 
-y = f[int]  # E: Type application is only supported for generic classes
+y = f[int]  # E: Type application is only supported for generic classes and type aliases
 [out]
 
 
@@ -1004,7 +1004,7 @@ reveal_type(y)  # N: Revealed type is "builtins.int"
 
 U[int]  # E: Bad number of arguments for type alias, expected 0, given 1
 O[int]  # E: Bad number of arguments for type alias, expected 0, given 1 \
-        # E: Type application is only supported for generic classes
+        # E: Type application is only supported for generic classes and type aliases
 
 [case testAliasesInClassBodyNormalVsSubscripted]
 
@@ -1072,9 +1072,9 @@ reveal_type(ts) # N: Revealed type is "Any"
 us = UA.x # E: "<typing special form>" has no attribute "x"
 reveal_type(us) # N: Revealed type is "Any"
 
-xx = CA[str] + 1  # E: Type application is only supported for generic classes
-yy = TA[str]()  # E: Type application is only supported for generic classes
-zz = UA[str].x  # E: Type application is only supported for generic classes
+xx = CA[str] + 1  # E: Type application is only supported for generic classes and type aliases
+yy = TA[str]()  # E: Type application is only supported for generic classes and type aliases
+zz = UA[str].x  # E: Type application is only supported for generic classes and type aliases
 [builtins fixtures/tuple.pyi]
 [typing fixtures/typing-medium.pyi]
 [out]
diff --git a/test-data/unit/check-parameter-specification.test b/test-data/unit/check-parameter-specification.test
@@ -92,7 +92,7 @@ class B(Generic[P]): ...
 Other = B[P]
 
 T = TypeVar('T', bound=Alias[..., Any])
-Alias[..., Any]  # E: Type application is only supported for generic classes
+Alias[..., Any]  # E: Type application is only supported for generic classes and type aliases
 B[...]
 Other[...]
 [builtins fixtures/paramspec.pyi]
diff --git a/test-data/unit/check-typevar-tuple.test b/test-data/unit/check-typevar-tuple.test
@@ -2763,6 +2763,6 @@ T = TypeVar('T')
 
 def func(d: Callable[[Unpack[Ts]], T]) -> T: ...
 
-y = func[1, int] # E: Type application is only supported for generic classes \
+y = func[1, int] # E: Type application is only supported for generic classes and type aliases \
                  # E: Invalid type: try using Literal[1] instead?
 [builtins fixtures/tuple.pyi]

Original file line number	Diff line number	Diff line change
`@@ -121,7 +121,7 @@ def with_additional_msg(self, info: str) -> ErrorMessage:`
`121`	`121`	`"Function is missing a type annotation", codes.NO_UNTYPED_DEF`
`122`	`122`	`)`
`123`	`123`	`ONLY_CLASS_APPLICATION: Final = ErrorMessage(`
`124`		`- "Type application is only supported for generic classes"`
	`124`	`+ "Type application is only supported for generic classes and type aliases"`
`125`	`125`	`)`
`126`	`126`	`RETURN_TYPE_EXPECTED: Final = ErrorMessage(`
`127`	`127`	`"Function is missing a return type annotation", codes.NO_UNTYPED_DEF`