Document and test .getter rejection

Author: sterliakov

mypy/semanal.py

@@ -1575,6 +1575,12 @@ def _is_valid_property_decorator(
         if not isinstance(deco.expr, NameExpr) or deco.expr.name != property_name:
             return False
         if deco.name not in {"setter", "deleter"}:
+            # This intentionally excludes getter. While `@prop.getter` is valid at
+            # runtime, that would mean replacing the already processed getter type.
+            # Such usage is almost definitely a mistake (except for overrides in
+            # subclasses but we don't support them anyway) and might be a typo
+            # (only one letter away from `setter`), it's likely almost never used,
+            # so supporting it properly won't pay off.
             return False
         return True
 

test-data/unit/check-classes.test

@@ -1624,7 +1624,6 @@ class A:
 [builtins fixtures/property.pyi]
 
 [case testPropertyNameIsChecked]
-import typing
 class A:
     @property
     def f(self) -> str: ...
@@ -1651,14 +1650,21 @@ class C:
 [builtins fixtures/property.pyi]
 
 [case testPropertyAttributeIsChecked]
-import typing
 class A:
     @property
     def f(self) -> str: ...
     @f.unknown  # E: Only supported top decorators are @f.setter and @f.deleter
     def f(self, val: str) -> None: ...
 [builtins fixtures/property.pyi]
 
+[case testPropertyGetterDecoratorIsRejected]
+class A:
+    @property
+    def f(self) -> str: ...
+    @f.getter  # E: Only supported top decorators are @f.setter and @f.deleter
+    def f(self, val: str) -> None: ...
+[builtins fixtures/property.pyi]
+
 [case testDynamicallyTypedProperty]
 import typing
 class A: