Make sure param completions work the right way

jedi/api/completion.py

@@ -216,6 +216,8 @@ class Completion:
             elif nonterminals[-1] in ('trailer', 'dotted_name') and nodes[-1] == '.':
                 dot = self._module_node.get_leaf_for_position(self._position)
                 completion_names += self._complete_trailer(dot.get_previous_leaf())
+            elif self._is_parameter_completion():
+                pass
             else:
                 completion_names += self._complete_global_scope()
                 completion_names += self._complete_inherited(is_function=False)
@@ -234,6 +236,19 @@ class Completion:
 
         return completion_names
 
+    def _is_parameter_completion(self):
+        tos = self.stack[-1]
+        if tos.nonterminal == 'lambdef' and len(tos.nodes) == 1:
+            # We are at the position `lambda `, where basically the next node
+            # is a param.
+            return True
+        if tos.nonterminal in 'parameters':
+            # Basically we are at the position `foo(`, there's nothing there
+            # yet, so we have no `typedargslist`.
+            return True
+        # var args is for lambdas and typed args for normal functions
+        return tos.nonterminal in ('typedargslist', 'varargslist') and tos.nodes[-1] == ','
+
     def _complete_keywords(self, allowed_transitions):
         for k in allowed_transitions:
             if isinstance(k, str) and k.isalpha():