Improve a bit of dataclasses support, so at least the attributes can be seen

see #1213

jedi/plugins/stdlib.py

@@ -599,4 +599,8 @@ _implemented = {
         # being used instead. This only matters for 3.7+.
         '_alias': lambda obj, arguments: NO_CONTEXTS,
     },
+    'dataclasses': {
+        # For now this works at least better than Jedi trying to understand it.
+        'dataclass': lambda obj, arguments: NO_CONTEXTS,
+    },
 }

test/completion/decorators.py

@@ -310,11 +310,14 @@ follow_statement(1)
 # class decorators should just be ignored
 @should_ignore
 class A():
+    x = 3
     def ret(self):
         return 1
 
 #? int()
 A().ret()
+#? int()
+A().x
 
 
 # -----------------

test/completion/pep0526_variables.py

@@ -103,3 +103,13 @@ d.var_class1
 d.var_class2
 #? []
 d.int
+
+
+
+import dataclasses
+@dataclasses.dataclass
+class DC:
+    name: int = 1
+
+#? int()
+DC().name