Fix signature to_string

jedi/evaluate/names.py

@@ -184,12 +184,19 @@ class ParamName(ParamNameInterface, AbstractTreeName):
             return Parameter.VAR_KEYWORD
 
         parent = tree_param.parent
+        param_appeared = False
         for p in parent.children:
+            if param_appeared:
+                if p == '/':
+                    return Parameter.POSITIONAL_ONLY
+            else:
+                if p == '*':
+                    return Parameter.KEYWORD_ONLY
                 if p.type == 'param':
                     if p.star_count:
                         return Parameter.KEYWORD_ONLY
                     if p == tree_param:
-                    break
+                        param_appeared = True
         return Parameter.POSITIONAL_OR_KEYWORD
 
     def to_string(self):

jedi/evaluate/signature.py

@@ -25,8 +25,10 @@ class AbstractSignature(object):
                     yield '/'
                     is_positional = False
 
-                if kind == Parameter.KEYWORD_ONLY and not is_kw_only:
-                    yield '*,'
+                if kind == Parameter.VAR_POSITIONAL:
+                    is_kw_only = True
+                elif kind == Parameter.KEYWORD_ONLY and not is_kw_only:
+                    yield '*'
                     is_kw_only = True
 
                 yield n.to_string()

test/test_evaluate/test_signature.py

@@ -32,3 +32,21 @@ def test_compiled_signature(Script, environment, code, sig, names, op, version):
     signature, = compiled.get_signatures()
     assert signature.to_string() == sig
     assert [n.string_name for n in signature.get_param_names()] == names
+
+
+@pytest.mark.parametrize(
+    'code, expected', [
+        ('def f(a, * args, x): pass\n f(', 'f(a, *args, x)'),
+        ('def f(a, *, x): pass\n f(', 'f(a, *, x)'),
+        ('def f(*, x= 3,**kwargs): pass\n f(', 'f(*, x=3, **kwargs)'),
+        ('def f(x,/,y,* ,z): pass\n f(', 'f(x, /, y, *, z)'),
+        ('def f(a, /, *, x=3, **kwargs): pass\n f(', 'f(a, /, *, x=3, **kwargs)'),
+    ]
+)
+def test_tree_signature(Script, environment, code, expected):
+    # Only test this in the latest version, because of /
+    if environment.version_info < (3, 8):
+        pytest.skip()
+
+    sig, = Script(code).call_signatures()
+    assert expected == sig._signature.to_string()