From 2a365b6156f7651e1b795cc88e128f288e4130d6 Mon Sep 17 00:00:00 2001
From: Simon Willison <swillison@gmail.com>
Date: Mon, 14 May 2018 19:09:09 -0300
Subject: [PATCH] path_with_added_args now works with multiple existing args

---
 datasette/utils.py  | 4 ++--
 tests/test_utils.py | 3 +++
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/datasette/utils.py b/datasette/utils.py
index 0e0c388b..e5bdf589 100644
--- a/datasette/utils.py
+++ b/datasette/utils.py
@@ -149,10 +149,10 @@ def path_with_added_args(request, args, path=None):
     path = path or request.path
     if isinstance(args, dict):
         args = args.items()
-    arg_keys = set(a[0] for a in args)
+    args_to_remove = {k for k, v in args if v is None}
     current = []
     for key, value in urllib.parse.parse_qsl(request.query_string):
-        if key not in arg_keys:
+        if key not in args_to_remove:
             current.append((key, value))
     current.extend([
         (key, value)
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 0d6bb2d1..bbae4f08 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -35,6 +35,9 @@ def test_urlsafe_components(path, expected):
     ('/?_facet=state&_facet=city&state=MI', (
         ('city', 'Detroit'),
     ), '/?_facet=state&_facet=city&state=MI&city=Detroit'),
+    ('/?_facet=state&_facet=city', (
+        ('_facet', 'planet_id'),
+    ), '/?_facet=state&_facet=city&_facet=planet_id'),
 ])
 def test_path_with_added_args(path, added_args, expected):
     request = Request(