Inspection to warn about decorators nested over @{class,static}method.

python/src/com/jetbrains/python/PyBundle.properties

@@ -135,6 +135,10 @@ INSP.usually.named.self=Usually first parameter of a method is named 'self'
 INSP.usually.named.cls=Usually first parameter of such methods is named 'cls'
 INSP.first.param.must.not.be.tuple=First parameter of a non-static method must not be a tuple
 
+# PyNestedDecoratorsInspection
+INSP.NAME.nested.decorators=Problematic nesting of decorators
+INSP.decorator.receives.unexpected.builtin=This decorator will not receive a callable it may expect; the built-in decorator returns a special object 
+
 # PyRedeclarationInspection
 INSP.NAME.redeclaration=Names redeclared without usage
 INSP.shadows.same.named.$0.above=Shadows same-named {0} above

python/src/com/jetbrains/python/inspections/PythonInspectionToolProvider.java

@@ -43,7 +43,8 @@ public class PythonInspectionToolProvider implements InspectionToolProvider {
       PyCallingNonCallableInspection.class,
       PyPropertyAccessInspection.class,
       PyPropertyDefinitionInspection.class,
-      PyInconsistentIndentationInspection.class
+      PyInconsistentIndentationInspection.class,
+      PyNestedDecoratorsInspection.class,
     };
   }
 }

python/testData/inspections/PyNestedDecoratorsInspection/expected.xml

@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<problems>
+  <problem>
+    <file>decorated.py</file>
+    <line>25</line>
+    <description>This decorator will not receive a callable it may expect; the built-in decorator returns a special object</description>
+  </problem>
+  <problem>
+    <file>decorated.py</file>
+    <line>30</line>
+    <description>This decorator will not receive a callable it may expect; the built-in decorator returns a special object</description>
+  </problem>
+  <problem>
+    <file>decorated.py</file>
+    <line>35</line>
+    <description>This decorator will not receive a callable it may expect; the built-in decorator returns a special object</description>
+  </problem>
+  <problem>
+    <file>decorated.py</file>
+    <line>40</line>
+    <description>This decorator will not receive a callable it may expect; the built-in decorator returns a special object</description>
+  </problem>
+  <problem>
+    <file>decorated.py</file>
+    <line>47</line>
+    <description>This decorator will not receive a callable it may expect; the built-in decorator returns a special object</description>
+  </problem>
+</problems>

python/testData/inspections/PyNestedDecoratorsInspection/src/decorated.py

@@ -0,0 +1,51 @@
+def innocent(f):
+  "A transparent deco"
+  print("I'm innocent!")
+  return f
+
+class A(object):
+  def f1(self): # nothing
+    pass
+
+  @innocent
+  @innocent
+  def f2(cls): # nothing
+    pass
+
+  @classmethod
+  @innocent
+  def f2(cls): # nothing
+    pass
+
+  @staticmethod
+  @innocent
+  def f4(): # nothing
+    pass
+
+  @innocent # warn
+  @classmethod
+  def f3(cls):
+    pass
+
+  @innocent # warn
+  @staticmethod
+  def f5():
+    pass
+
+  @classmethod # warn
+  @staticmethod
+  def f2(cls):
+    pass
+
+  @innocent  # warn
+  @classmethod
+  @innocent
+  def f2(cls):
+    pass
+
+  @innocent
+  @innocent  # warn
+  @classmethod
+  @innocent
+  def f2(cls):
+    pass