check for class methods declared without a decorator

related to the issue #675

9 files changed, 76 insertions, 6 deletions

diff --git a/pylint/checkers/classes.py b/pylint/checkers/classes.py
index 86ccb19..98a13bf 100644
--- a/pylint/checkers/classes.py
+++ b/pylint/checkers/classes.py
@@ -262,7 +262,10 @@ MSGS = {
     'E0241': ('Duplicate bases for class %r',
               'duplicate-bases',
               'Used when a class has duplicate bases.'),
-
+    'R0202': ('Consider using a decorator instead of calling classmethod',
+              'no-classmethod-decorator',
+              'Used when a class method is defined without using the decorator '
+              'syntax.'),
     }
 
 
@@ -613,17 +616,47 @@ a metaclass class method.'}
                     self.add_message('assigning-non-slot',
                                      args=(node.attrname, ), node=node)
 
-    @check_messages('protected-access')
+    @check_messages('protected-access', 'no-classmethod-decorator')
     def visit_assign(self, assign_node):
+        self._check_classmethod_declaration(assign_node)
         node = assign_node.targets[0]
         if not isinstance(node, astroid.AssignAttr):
             return
 
         if self.is_first_attr(node):
             return
-
         self._check_protected_attribute_access(node)
 
+    def _check_classmethod_declaration(self, node):
+        """checks for uses of classmethod() instead of @classmethod decorator
+
+        A message will be emitted only if the assignment is at a class scope
+        and only if the classmethod's argument belongs to the class where it
+        is defined.
+        `node` is an assign node.
+        """
+        if not isinstance(node.value, astroid.Call):
+            return
+        # check the function called is "classmethod"
+        func = node.value.func
+        if not isinstance(func, astroid.Name) or not func.name == 'classmethod':
+            return
+        # assignment must be at a class scope
+        parent_class = node.parent
+        if not isinstance(parent_class, astroid.ClassDef):
+            return
+        # Check if the arg passed to classmethod is a class member
+        classmeth_arg = node.value.args[0]
+        if not isinstance(classmeth_arg, astroid.Name):
+            return
+        method_name = classmeth_arg.name
+        for member in parent_class.get_children():
+            if (isinstance(member, astroid.FunctionDef) and
+                    method_name == member.name):
+                self.add_message('no-classmethod-decorator',
+                                 node=node.targets[0])
+                break
+
     def _check_protected_attribute_access(self, node):
         '''Given an attribute access node (set or get), check if attribute
         access is legitimate. Call _check_first_attr with node before calling
diff --git a/pylint/test/functional/access_to_protected_members.py b/pylint/test/functional/access_to_protected_members.py
index 9c92306..fd96baf 100644
--- a/pylint/test/functional/access_to_protected_members.py
+++ b/pylint/test/functional/access_to_protected_members.py
@@ -1,4 +1,5 @@
 # pylint: disable=too-few-public-methods, W0231, print-statement
+# pylint: disable=no-classmethod-decorator
 """Test external access to protected class members."""
 from __future__ import print_function
 
diff --git a/pylint/test/functional/access_to_protected_members.txt b/pylint/test/functional/access_to_protected_members.txt
index 123c1dd..7ba601b 100644
--- a/pylint/test/functional/access_to_protected_members.txt
+++ b/pylint/test/functional/access_to_protected_members.txt
@@ -1,5 +1,5 @@
-protected-access:18:MyClass.test:Access to a protected member _haha of a client class
-protected-access:40::Access to a protected member _protected of a client class
+protected-access:19:MyClass.test:Access to a protected member _haha of a client class
 protected-access:41::Access to a protected member _protected of a client class
-protected-access:42::Access to a protected member _cls_protected of a client class
+protected-access:42::Access to a protected member _protected of a client class
 protected-access:43::Access to a protected member _cls_protected of a client class
+protected-access:44::Access to a protected member _cls_protected of a client class
diff --git a/pylint/test/functional/no_classmethod_decorator.py b/pylint/test/functional/no_classmethod_decorator.py
new file mode 100644
index 0000000..205594d
--- /dev/null
+++ b/pylint/test/functional/no_classmethod_decorator.py
@@ -0,0 +1,28 @@
+"""Checks classes methods are declared with a decorator if whithin the class
+scope and if classmethod's argument is a member of the class
+"""
+
+# pylint: disable=too-few-public-methods
+
+class MyClass(object):
+    """Some class"""
+    def __init__(self):
+        pass
+
+    def cmethod(cls):
+        """class method-to-be"""
+    cmethod = classmethod(cmethod) # [no-classmethod-decorator]
+
+    @classmethod
+    def my_second_method(cls):
+        """correct class method definition"""
+
+def helloworld():
+    """says hello"""
+    print 'hello world'
+
+MyClass.new_class_method = classmethod(helloworld)
+
+class MyOtherClass(object):
+    """Some other class"""
+    _make = classmethod(tuple.__new__)
diff --git a/pylint/test/functional/no_classmethod_decorator.txt b/pylint/test/functional/no_classmethod_decorator.txt
new file mode 100644
index 0000000..8c1060f
--- /dev/null
+++ b/pylint/test/functional/no_classmethod_decorator.txt
@@ -0,0 +1 @@
+no-classmethod-decorator:14:MyClass:Consider using a decorator instead of calling classmethod
diff --git a/pylint/test/input/func_noerror_classes_protected_member_access.py b/pylint/test/input/func_noerror_classes_protected_member_access.py
index eeff97d..670e3e8 100644
--- a/pylint/test/input/func_noerror_classes_protected_member_access.py
+++ b/pylint/test/input/func_noerror_classes_protected_member_access.py
@@ -3,6 +3,7 @@
 """
 __revision__ = 1
 
+# pylint: disable=no-classmethod-decorator
 class A3123(object):
     """oypuee"""
     _protected = 1
diff --git a/pylint/test/input/func_noerror_static_method.py b/pylint/test/input/func_noerror_static_method.py
index ef21cb9..8a7a0a2 100644
--- a/pylint/test/input/func_noerror_static_method.py
+++ b/pylint/test/input/func_noerror_static_method.py
@@ -3,6 +3,7 @@
 from __future__ import print_function
 __revision__ = ''
 
+#pylint: disable=no-classmethod-decorator
 class MyClass(object):
     """doc
     """
diff --git a/pylint/test/messages/func_e0203.txt b/pylint/test/messages/func_e0203.txt
index c330ffa..96769de 100644
--- a/pylint/test/messages/func_e0203.txt
+++ b/pylint/test/messages/func_e0203.txt
@@ -1 +1,2 @@
 C: 12:Abcd.abcd: Class method abcd should have 'cls' as first argument
+R: 15:Abcd: Consider using a decorator instead of calling classmethod
diff --git a/pylint/test/messages/func_first_arg.txt b/pylint/test/messages/func_first_arg.txt
index 75090dd..ba4efb8 100644
--- a/pylint/test/messages/func_first_arg.txt
+++ b/pylint/test/messages/func_first_arg.txt
@@ -3,3 +3,7 @@ C: 18:Obj.class2: Class method class2 should have 'cls' as first argument
 C: 25:Meta.__new__: Metaclass class method __new__ should have 'mcs' as first argument
 C: 32:Meta.method2: Metaclass method method2 should have 'cls' as first argument
 C: 40:Meta.class2: Metaclass class method class2 should have 'mcs' as first argument
+R: 16:Obj: Consider using a decorator instead of calling classmethod
+R: 20:Obj: Consider using a decorator instead of calling classmethod
+R: 38:Meta: Consider using a decorator instead of calling classmethod
+R: 42:Meta: Consider using a decorator instead of calling classmethod