Check property decorators stricter (#19313)

Fixes #19312. Fixes #18327.

Only accept `@current_prop_name.{setter,deleter}` as property-related
decorators.

Author: sterliakov

mypy/semanal.py

@@ -1527,33 +1527,33 @@ def analyze_property_with_multi_part_definition(
         assert isinstance(first_item, Decorator)
         deleted_items = []
         bare_setter_type = None
+        func_name = first_item.func.name
         for i, item in enumerate(items[1:]):
             if isinstance(item, Decorator):
                 item.func.accept(self)
                 if item.decorators:
                     first_node = item.decorators[0]
-                    if isinstance(first_node, MemberExpr):
+                    if self._is_valid_property_decorator(first_node, func_name):
+                        # Get abstractness from the original definition.
+                        item.func.abstract_status = first_item.func.abstract_status
                         if first_node.name == "setter":
                             # The first item represents the entire property.
                             first_item.var.is_settable_property = True
-                            # Get abstractness from the original definition.
-                            item.func.abstract_status = first_item.func.abstract_status
                             setter_func_type = function_type(
                                 item.func, self.named_type("builtins.function")
                             )
                             assert isinstance(setter_func_type, CallableType)
                             bare_setter_type = setter_func_type
                             defn.setter_index = i + 1
-                        if first_node.name == "deleter":
-                            item.func.abstract_status = first_item.func.abstract_status
                         for other_node in item.decorators[1:]:
                             other_node.accept(self)
                     else:
                         self.fail(
-                            f"Only supported top decorator is @{first_item.func.name}.setter", item
+                            f'Only supported top decorators are "@{func_name}.setter" and "@{func_name}.deleter"',
+                            first_node,
                         )
             else:
-                self.fail(f'Unexpected definition for property "{first_item.func.name}"', item)
+                self.fail(f'Unexpected definition for property "{func_name}"', item)
                 deleted_items.append(i + 1)
         for i in reversed(deleted_items):
             del items[i]
@@ -1567,6 +1567,23 @@ def analyze_property_with_multi_part_definition(
                         )
         return bare_setter_type
 
+    def _is_valid_property_decorator(
+        self, deco: Expression, property_name: str
+    ) -> TypeGuard[MemberExpr]:
+        if not isinstance(deco, MemberExpr):
+            return False
+        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
+
     def add_function_to_symbol_table(self, func: FuncDef | OverloadedFuncDef) -> None:
         if self.is_class_scope():
             assert self.type is not None

test-data/unit/check-classes.test

@@ -772,7 +772,7 @@ class A:
 class B(A):
     @property
     def f(self) -> Callable[[object], None]: pass
-    @func.setter
+    @f.setter
     def f(self, x: object) -> None: pass
 [builtins fixtures/property.pyi]
 
@@ -786,7 +786,7 @@ class A:
 class B(A):
     @property
     def f(self) -> Callable[[object], None]: pass
-    @func.setter
+    @f.setter
     def f(self, x: object) -> None: pass
 [builtins fixtures/property.pyi]
 
@@ -1622,7 +1622,81 @@ class A:
         self.x = '' # E: Incompatible types in assignment (expression has type "str", variable has type "int")
         return ''
 [builtins fixtures/property.pyi]
+
+[case testPropertyNameIsChecked]
+class A:
+    @property
+    def f(self) -> str: ...
+    @not_f.setter  # E: Only supported top decorators are "@f.setter" and "@f.deleter"
+    def f(self, val: str) -> None: ...
+
+a = A()
+reveal_type(a.f)  # N: Revealed type is "builtins.str"
+a.f = ''  # E: Property "f" defined in "A" is read-only
+
+class B:
+    @property
+    def f(self) -> str: ...
+    @not_f.deleter  # E: Only supported top decorators are "@f.setter" and "@f.deleter"
+    def f(self) -> None: ...
+
+class C:
+    @property
+    def f(self) -> str: ...
+    @not_f.setter  # E: Only supported top decorators are "@f.setter" and "@f.deleter"
+    def f(self, val: str) -> None: ...
+    @not_f.deleter  # E: Only supported top decorators are "@f.setter" and "@f.deleter"
+    def f(self) -> None: ...
+[builtins fixtures/property.pyi]
+
+[case testPropertyAttributeIsChecked]
+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: ...
+    @f.bad.setter  # E: Only supported top decorators are "@f.setter" and "@f.deleter"
+    def f(self, val: str) -> None: ...
+    @f  # E: Only supported top decorators are "@f.setter" and "@f.deleter"
+    def f(self, val: str) -> None: ...
+    @int  # E: Only supported top decorators are "@f.setter" and "@f.deleter"
+    def f(self, val: str) -> None: ...
+[builtins fixtures/property.pyi]
+
+[case testPropertyNameAndAttributeIsCheckedPretty]
+# flags: --pretty
+class A:
+    @property
+    def f(self) -> str: ...
+    @not_f.setter
+    def f(self, val: str) -> None: ...
+    @not_f.deleter
+    def f(self) -> None: ...
+
+class B:
+    @property
+    def f(self) -> str: ...
+    @f.unknown
+    def f(self, val: str) -> None: ...
+[builtins fixtures/property.pyi]
 [out]
+main:5: error: Only supported top decorators are "@f.setter" and "@f.deleter"
+        @not_f.setter
+         ^~~~~~~~~~~~
+main:7: error: Only supported top decorators are "@f.setter" and "@f.deleter"
+        @not_f.deleter
+         ^~~~~~~~~~~~~
+main:13: error: Only supported top decorators are "@f.setter" and "@f.deleter"
+        @f.unknown
+         ^~~~~~~~~
+
+[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
@@ -7739,7 +7813,7 @@ class A:
     def y(self) -> int: ...
     @y.setter
     def y(self, value: int) -> None: ...
-    @dec  # E: Only supported top decorator is @y.setter
+    @dec  # E: Only supported top decorators are "@y.setter" and "@y.deleter"
     def y(self) -> None: ...
 
 reveal_type(A().y)  # N: Revealed type is "builtins.int"

test-data/unit/check-functions.test

@@ -2752,7 +2752,7 @@ class B:
     @property
     @dec
     def f(self) -> int: pass
-    @dec # E: Only supported top decorator is @f.setter
+    @dec # E: Only supported top decorators are "@f.setter" and "@f.deleter"
     @f.setter
     def f(self, v: int) -> None: pass
 
@@ -2764,7 +2764,6 @@ class C:
     @dec
     def f(self, v: int) -> None: pass
 [builtins fixtures/property.pyi]
-[out]
 
 [case testInvalidArgCountForProperty]
 from typing import Callable, TypeVar
@@ -2783,7 +2782,6 @@ class A:
     @property
     def h(self, *args, **kwargs) -> int: pass   # OK
 [builtins fixtures/property.pyi]
-[out]
 
 [case testSubtypingUnionGenericBounds]
 from typing import Callable, TypeVar, Union, Sequence

test-data/unit/semanal-errors.test

@@ -1236,7 +1236,7 @@ class A:
     @overload  # E: Decorators on top of @property are not supported
     @property
     def f(self) -> int: pass
-    @property  # E: Only supported top decorator is @f.setter
+    @property  # E: Only supported top decorators are "@f.setter" and "@f.deleter"
     @overload
     def f(self) -> int: pass
 [builtins fixtures/property.pyi]