Fix docstrings for method decorators, fixes #1621

jedi/inference/value/decorator.py

@@ -3,7 +3,7 @@ Decorators are not really values, however we need some wrappers to improve
 docstrings and other things around decorators.
 '''
 
-from jedi.inference.base_value import ValueWrapper
+from jedi.inference.base_value import ValueWrapper, ValueSet
 
 
 class Decoratee(ValueWrapper):
@@ -13,3 +13,9 @@ class Decoratee(ValueWrapper):
 
     def py__doc__(self):
         return self._original_value.py__doc__()
+
+    def py__get__(self, instance, class_value):
+        return ValueSet(
+            Decoratee(v, self._original_value)
+            for v in self._wrapped_value.py__get__(instance, class_value)
+        )

jedi/plugins/stdlib.py

@@ -119,7 +119,9 @@ def execute(callback):
             else:
                 return call()
 
-            if value.is_bound_method():
+            if value.is_bound_method() or value.is_instance():
+                # value can be an instance for example if it is a partial
+                # object.
                 return call()
 
             # for now we just support builtin functions.

test/test_inference/test_docstring.py

@@ -422,6 +422,27 @@ def test_decorator(Script):
     assert d.docstring(raw=True) == 'Nice docstring'
 
 
+def test_method_decorator(Script):
+    code = dedent('''
+        def decorator(func):
+            @wraps(func)
+            def wrapper(*args, **kwargs):
+                """wrapper docstring"""
+                return func(*args, **kwargs)
+            return wrapper
+
+        class Foo():
+            @decorator
+            def check_user(self, f):
+                """Nice docstring"""
+                pass
+
+        Foo().check_user''')
+
+    d, = Script(code).infer()
+    assert d.docstring() == 'check_user(f)\n\nNice docstring'
+
+
 def test_partial(Script):
     code = dedent('''
         def foo():