Generalize class/static method and property alias support (#19297)

Fixes #6700

This is another followup for the `checkmember` work. Currently, we only
support non-instance method aliasing in few very specific cases. I am
making this support general.

Author: ilevkivskyi

mypy/checker.py

@@ -4400,9 +4400,9 @@ def set_inferred_type(self, var: Var, lvalue: Lvalue, type: Type) -> None:
         refers to the variable (lvalue). If var is None, do nothing.
         """
         if var and not self.current_node_deferred:
-            # TODO: should we also set 'is_ready = True' here?
             var.type = type
             var.is_inferred = True
+            var.is_ready = True
             if var not in self.var_decl_frames:
                 # Used for the hack to improve optional type inference in conditionals
                 self.var_decl_frames[var] = {frame.id for frame in self.binder.frames}
@@ -4412,9 +4412,23 @@ def set_inferred_type(self, var: Var, lvalue: Lvalue, type: Type) -> None:
                     self.inferred_attribute_types[lvalue.def_var] = type
             self.store_type(lvalue, type)
             p_type = get_proper_type(type)
-            if isinstance(p_type, CallableType) and is_node_static(p_type.definition):
-                # TODO: handle aliases to class methods (similarly).
-                var.is_staticmethod = True
+            definition = None
+            if isinstance(p_type, CallableType):
+                definition = p_type.definition
+            elif isinstance(p_type, Overloaded):
+                # Randomly select first item, if items are different, there will
+                # be an error during semantic analysis.
+                definition = p_type.items[0].definition
+            if definition:
+                if is_node_static(definition):
+                    var.is_staticmethod = True
+                elif is_classmethod_node(definition):
+                    var.is_classmethod = True
+                elif is_property(definition):
+                    var.is_property = True
+                    if isinstance(p_type, Overloaded):
+                        # TODO: in theory we can have a property with a deleter only.
+                        var.is_settable_property = True
 
     def set_inference_error_fallback_type(self, var: Var, lvalue: Lvalue, type: Type) -> None:
         """Store best known type for variable if type inference failed.
@@ -8531,15 +8545,21 @@ def visit_type_alias_type(self, t: TypeAliasType) -> Type:
         return t.copy_modified(args=[a.accept(self) for a in t.args])
 
 
+def is_classmethod_node(node: Node | None) -> bool | None:
+    """Find out if a node describes a classmethod."""
+    if isinstance(node, FuncDef):
+        return node.is_class
+    if isinstance(node, Var):
+        return node.is_classmethod
+    return None
+
+
 def is_node_static(node: Node | None) -> bool | None:
     """Find out if a node describes a static function method."""
-
     if isinstance(node, FuncDef):
         return node.is_static
-
     if isinstance(node, Var):
         return node.is_staticmethod
-
     return None
 
 
@@ -8786,6 +8806,8 @@ def is_static(func: FuncBase | Decorator) -> bool:
 
 
 def is_property(defn: SymbolNode) -> bool:
+    if isinstance(defn, FuncDef):
+        return defn.is_property
     if isinstance(defn, Decorator):
         return defn.func.is_property
     if isinstance(defn, OverloadedFuncDef):

mypy/checkmember.py

@@ -371,8 +371,6 @@ def analyze_instance_member_access(
                     signature, mx.self_type, method.is_class, mx.context, name, mx.msg
                 )
                 signature = bind_self(signature, mx.self_type, is_classmethod=method.is_class)
-        # TODO: should we skip these steps for static methods as well?
-        # Since generic static methods should not be allowed.
         typ = map_instance_to_supertype(typ, method.info)
         member_type = expand_type_by_instance(signature, typ)
         freeze_all_type_vars(member_type)
@@ -1224,8 +1222,11 @@ def analyze_class_attribute_access(
             #     C[int].x -> int
             t = erase_typevars(expand_type_by_instance(t, isuper), {tv.id for tv in def_vars})
 
-        is_classmethod = (is_decorated and cast(Decorator, node.node).func.is_class) or (
-            isinstance(node.node, SYMBOL_FUNCBASE_TYPES) and node.node.is_class
+        is_classmethod = (
+            (is_decorated and cast(Decorator, node.node).func.is_class)
+            or (isinstance(node.node, SYMBOL_FUNCBASE_TYPES) and node.node.is_class)
+            or isinstance(node.node, Var)
+            and node.node.is_classmethod
         )
         is_staticmethod = (is_decorated and cast(Decorator, node.node).func.is_static) or (
             isinstance(node.node, SYMBOL_FUNCBASE_TYPES) and node.node.is_static
@@ -1237,7 +1238,12 @@ def analyze_class_attribute_access(
             is_trivial_self = node.node.func.is_trivial_self and not node.node.decorators
         elif isinstance(node.node, (FuncDef, OverloadedFuncDef)):
             is_trivial_self = node.node.is_trivial_self
-        if isinstance(t, FunctionLike) and is_classmethod and not is_trivial_self:
+        if (
+            isinstance(t, FunctionLike)
+            and is_classmethod
+            and not is_trivial_self
+            and not t.bound()
+        ):
             t = check_self_arg(t, mx.self_type, False, mx.context, name, mx.msg)
         t = add_class_tvars(
             t,
@@ -1406,7 +1412,7 @@ class B(A[str]): pass
         tvars = original_vars if original_vars is not None else []
         if not mx.preserve_type_var_ids:
             t = freshen_all_functions_type_vars(t)
-        if is_classmethod:
+        if is_classmethod and not t.is_bound:
             if is_trivial_self:
                 t = bind_self_fast(t, mx.self_type)
             else:

test-data/unit/check-callable.test

@@ -587,6 +587,54 @@ class C(B):
 class B: ...
 [builtins fixtures/classmethod.pyi]
 
+[case testClassMethodAliasInClass]
+from typing import overload
+
+class C:
+    @classmethod
+    def foo(cls) -> int: ...
+
+    bar = foo
+
+    @overload
+    @classmethod
+    def foo2(cls, x: int) -> int: ...
+    @overload
+    @classmethod
+    def foo2(cls, x: str) -> str: ...
+    @classmethod
+    def foo2(cls, x):
+        ...
+
+    bar2 = foo2
+
+reveal_type(C.bar)  # N: Revealed type is "def () -> builtins.int"
+reveal_type(C().bar)  # N: Revealed type is "def () -> builtins.int"
+reveal_type(C.bar2)  # N: Revealed type is "Overload(def (x: builtins.int) -> builtins.int, def (x: builtins.str) -> builtins.str)"
+reveal_type(C().bar2)  # N: Revealed type is "Overload(def (x: builtins.int) -> builtins.int, def (x: builtins.str) -> builtins.str)"
+[builtins fixtures/classmethod.pyi]
+
+[case testPropertyAliasInClassBody]
+class A:
+    @property
+    def f(self) -> int: ...
+
+    g = f
+
+    @property
+    def f2(self) -> int: ...
+    @f2.setter
+    def f2(self, val: int) -> None: ...
+
+    g2 = f2
+
+reveal_type(A().g)  # N: Revealed type is "builtins.int"
+reveal_type(A().g2)  # N: Revealed type is "builtins.int"
+A().g = 1  # E: Property "g" defined in "A" is read-only
+A().g2 = 1
+A().g2 = "no"  # E: Incompatible types in assignment (expression has type "str", variable has type "int")
+[builtins fixtures/property.pyi]
+
 [case testCallableUnionCallback]
 from typing import Union, Callable, TypeVar
 

test-data/unit/check-classes.test

@@ -4588,6 +4588,23 @@ reveal_type(a.a)  # N: Revealed type is "def (a: builtins.int)"
 reveal_type(a.c)  # N: Revealed type is "def (a: builtins.int)"
 [builtins fixtures/staticmethod.pyi]
 
+[case testClassStaticMethodIndirectOverloaded]
+from typing import overload
+class A:
+    @overload
+    @staticmethod
+    def a(x: int) -> int: ...
+    @overload
+    @staticmethod
+    def a(x: str) -> str: ...
+    @staticmethod
+    def a(x):
+        ...
+    c = a
+reveal_type(A.c)  # N: Revealed type is "Overload(def (x: builtins.int) -> builtins.int, def (x: builtins.str) -> builtins.str)"
+reveal_type(A().c)  # N: Revealed type is "Overload(def (x: builtins.int) -> builtins.int, def (x: builtins.str) -> builtins.str)"
+[builtins fixtures/staticmethod.pyi]
+
 [case testClassStaticMethodSubclassing]
 class A:
     @staticmethod