Avoid wrong random call signature completion, fixes #1433

jedi/api/completion.py

@@ -210,7 +210,15 @@ class Completion:
                 completion_names += self._global_completions()
                 completion_names += self._get_class_value_completions(is_function=False)
 
-            if 'trailer' in nonterminals:
+            # Apparently this looks like it's good enough to filter most cases
+            # so that signature completions don't randomly appear.
+            # To understand why this works, two things are important:
+            # 1. trailer with a `,` in it is either a subscript or an arglist.
+            # 2. If there's no `,`, it's at the start and only signatures start
+            #    with `(`. Other trailers could start with `.` or `[`.
+            # One thing that might not work is completion in decorator
+            # executions, but most people won't care about that.
+            if nodes[-1] in ['(', ','] and nonterminals[-1] in ('trailer', 'arglist'):
                 call_signatures = self._call_signatures_callback()
                 completion_names += get_call_signature_param_names(call_signatures)
 

jedi/inference/compiled/__init__.py

@@ -1,7 +1,7 @@
 from jedi._compatibility import unicode
 from jedi.inference.compiled.value import CompiledObject, CompiledName, \
     CompiledObjectFilter, CompiledValueName, create_from_access_path
-from jedi.inference.base_value import ValueWrapper, LazyValueWrapper
+from jedi.inference.base_value import LazyValueWrapper
 
 
 def builtin_from_name(inference_state, string):

test/completion/named_param.py

@@ -60,3 +60,23 @@ Test().test(blub=)
 
 #? 12 []
 any(iterable=)
+
+
+def foo(xyz):
+    pass
+
+#? 7 ['xyz']
+foo(xyz)
+# No completion should be possible if it's not a simple name
+#? 17 []
+x = " "; foo(x.xyz)
+#? 17 []
+x = " "; foo([xyz)
+#? 20 []
+x = " "; foo(z[f,xyz)
+#? 18 []
+x = " "; foo(z[xyz)
+#? 20 []
+x = " "; foo(xyz[xyz)
+#? 20 []
+x = " "; foo(xyz[(xyz)