Simplify language chooser (#328)

* Simplify language chooser

- Allows usage of i18n_patterns with prefix_default_language=False
- Change templatetag from simple tag to an inclusion tag
- Reduces complexity by relying on Django's behavior in the
  set_language view: it will translate any url passed as 'next'.
  This behavior has been present since Django 1.9.
- Remove individual forms for each language

Fixes #327

Reference: django/django@aa5ab11

* Add check to ensure LocaleMiddleware

* Remove check in favor of silent warning

* Fix template tag tests

admin_interface/templates/admin/base_site.html

@@ -186,7 +186,6 @@ <h1 id="site-name">
 {{ block.super }}
 {% get_admin_interface_theme as theme %}
 {% if theme.language_chooser_active %}
-    {% get_admin_interface_languages as languages %}
-    {% include "admin_interface/language_chooser.html" %}
+    {% admin_interface_language_chooser %}
 {% endif %}
 {% endblock %}

admin_interface/templates/admin_interface/language_chooser.html

@@ -1,18 +1,15 @@
 {% load admin_interface_tags %}
 
-{% if languages %}
+{% if set_language_url %}
 <div class="language-chooser {% if theme.language_chooser_control == 'minimal-select' %}minimal {% endif %}">
-    {% for language in languages %}
-    <form class="language-chooser-hidden-form" id="language-chooser-hidden-form-{{ language.code }}" action="{{ language.activation_url }}" method="POST">
+    <form class="language-chooser-select-form" action="{{ set_language_url }}" method="POST">
         {% csrf_token %}
-        <input name="language" type="hidden" value="{{ language.code }}">
-    </form>
-    {% endfor %}
-    <form class="language-chooser-select-form">
-        {% csrf_token %}
-        <select name="language" onchange="document.getElementById(String('language-chooser-hidden-form-' + this.value)).submit();">
-            {% for language in languages %}
-            <option value="{{ language.code }}" {% if language.active %}selected{% endif %}>{% if theme.language_chooser_display == 'code' %}{{ language.code|upper }}{% elif theme.language_chooser_display == 'name' %}{{ language.name }}{% endif %}</option>
+        <input type="hidden" name="next" value="{{ next }}">
+        <select name="language" onchange="this.form.submit();">
+            {% for code, language in LANGUAGES %}
+            <option value="{{ code }}" {% if code == LANGUAGE_CODE %}selected{% endif %}>
+                {% if theme.language_chooser_display == 'code' %}{{ code|upper }}{% elif theme.language_chooser_display == 'name' %}{{ language }}{% endif %}
+            </option>
             {% endfor %}
         </select>
     </form>

admin_interface/templatetags/admin_interface_tags.py

@@ -1,6 +1,7 @@
 import datetime
 import hashlib
 import re
+import warnings
 
 from django import template
 from django.conf import settings
@@ -16,45 +17,43 @@
 register = template.Library()
 
 
-@register.simple_tag(takes_context=True)
-def get_admin_interface_languages(context):
+@register.inclusion_tag("admin_interface/language_chooser.html", takes_context=True)
+def admin_interface_language_chooser(context):
     if not settings.USE_I18N:
         # i18n disabled
         return None
     if len(settings.LANGUAGES) < 2:
         # less than 2 languages
         return None
+    if "django.middleware.locale.LocaleMiddleware" not in settings.MIDDLEWARE:
+        warnings.warn(
+            "Language chooser requires 'django.middleware.locale.LocaleMiddleware' "
+            "in your MIDDLEWARE to work.",
+            stacklevel=1,
+        )
+        return None
     try:
-        set_language_url = reverse("set_language")
+        context["set_language_url"] = reverse("set_language")
     except NoReverseMatch:
-        # ImproperlyConfigured - must include i18n urls:
-        # urlpatterns += [url(r'^i18n/', include('django.conf.urls.i18n')),]
+        warnings.warn(
+            "Language chooser requires Django's `set_language` view: "
+            "`urlpatterns += [url(r'^i18n/', include('django.conf.urls.i18n'))]`.",
+            stacklevel=1,
+        )
         return None
     request = context.get("request", None)
     if not request:
         return None
+    context["LANGUAGES"] = settings.LANGUAGES
+
     full_path = request.get_full_path()
     admin_nolang_url = re.sub(r"^\/([\w]{2})([\-\_]{1}[\w]{2,4})?\/", "/", full_path)
-    if admin_nolang_url == full_path:
-        # ImproperlyConfigured - must include admin urls using i18n_patterns:
-        # from django.conf.urls.i18n import i18n_patterns
-        # urlpatterns += i18n_patterns(url(r'^admin/', admin.site.urls))
-        return None
-    langs_data = []
+
     default_lang_code = settings.LANGUAGE_CODE
     current_lang_code = translation.get_language() or default_lang_code
-    for language in settings.LANGUAGES:
-        lang_code = language[0].lower()
-        lang_name = language[1].title()
-        lang_data = {
-            "code": lang_code,
-            "name": lang_name,
-            "default": lang_code == default_lang_code,
-            "active": lang_code == current_lang_code,
-            "activation_url": f"{set_language_url}?next=/{lang_code}{admin_nolang_url}",
-        }
-        langs_data.append(lang_data)
-    return langs_data
+    context["LANGUAGE_CODE"] = current_lang_code
+    context["next"] = admin_nolang_url
+    return context
 
 
 @register.simple_tag()

tests/settings.py

@@ -26,6 +26,7 @@
     "django.contrib.messages.middleware.MessageMiddleware",
     "django.contrib.sessions.middleware.SessionMiddleware",
     "django.middleware.common.CommonMiddleware",
+    "django.middleware.locale.LocaleMiddleware",
 ]
 
 TEMPLATES = [

tests/test_templatetags.py

@@ -22,118 +22,70 @@ def tearDown(self):
     def __render_template(self, string, context=None):
         return Template(string).render(Context(context or {}))
 
-    def test_get_admin_interface_languages(self):
+    def test_admin_interface_language_chooser(self):
         context = Context({"request": self.request_factory.get("/en/admin/")})
-        languages = templatetags.get_admin_interface_languages(context)
+        context = templatetags.admin_interface_language_chooser(context)
+        languages = context["LANGUAGES"]
         expected_languages = [
-            {
-                "code": "de",
-                "name": "Deutsch",
-                "default": False,
-                "active": False,
-                "activation_url": "/i18n/setlang/?next=/de/admin/",
-            },
-            {
-                "code": "en",
-                "name": "English",
-                "default": True,
-                "active": True,
-                "activation_url": "/i18n/setlang/?next=/en/admin/",
-            },
-            {
-                "code": "es",
-                "name": "Español",
-                "default": False,
-                "active": False,
-                "activation_url": "/i18n/setlang/?next=/es/admin/",
-            },
-            {
-                "code": "fa",
-                "name": "Farsi",
-                "default": False,
-                "active": False,
-                "activation_url": "/i18n/setlang/?next=/fa/admin/",
-            },
-            {
-                "code": "fr",
-                "name": "Français",
-                "default": False,
-                "active": False,
-                "activation_url": "/i18n/setlang/?next=/fr/admin/",
-            },
-            {
-                "code": "it",
-                "name": "Italiano",
-                "default": False,
-                "active": False,
-                "activation_url": "/i18n/setlang/?next=/it/admin/",
-            },
-            {
-                "code": "pl",
-                "name": "Polski",
-                "default": False,
-                "active": False,
-                "activation_url": "/i18n/setlang/?next=/pl/admin/",
-            },
-            {
-                "code": "pt-BR",
-                "name": "Português",
-                "default": False,
-                "active": False,
-                "activation_url": "/i18n/setlang/?next=/pt-br/admin/",
-            },
-            {
-                "code": "ru",
-                "name": "Русский",
-                "default": False,
-                "active": False,
-                "activation_url": "/i18n/setlang/?next=/ru/admin/",
-            },
-            {
-                "code": "tr",
-                "name": "Türk",
-                "default": False,
-                "active": False,
-                "activation_url": "/i18n/setlang/?next=/tr/admin/",
-            },
+            ("de", "Deutsch"),
+            ("en", "English"),
+            ("es", "Español"),
+            ("fa", "Farsi"),
+            ("fr", "Français"),
+            ("it", "Italiano"),
+            ("pl", "Polski"),
+            ("pt-BR", "Português"),
+            ("ru", "Русский"),
+            ("tr", "Türk"),
         ]
         self.assertEqual(len(languages), len(expected_languages))
         self.assertEqual(languages[0], expected_languages[0])
         self.assertEqual(languages[1], expected_languages[1])
+        self.assertEqual(context["next"], "/admin/")
 
     @override_settings(
         USE_I18N=False,
     )
-    def test_get_admin_interface_languages_with_i18n_disabled(self):
+    def test_admin_interface_language_chooser_with_i18n_disabled(self):
         context = Context({"request": self.request_factory.get("/en/admin/")})
-        languages = templatetags.get_admin_interface_languages(context)
-        self.assertEqual(languages, None)
+        tag_context = templatetags.admin_interface_language_chooser(context)
+        self.assertEqual(tag_context, None)
 
     @override_settings(
         ROOT_URLCONF="tests.urls_without_i18n_patterns",
     )
-    def test_get_admin_interface_languages_without_i18n_url_patterns(self):
+    def test_admin_interface_language_chooser_without_i18n_url_patterns(self):
         context = Context({"request": self.request_factory.get("/en/admin/")})
-        languages = templatetags.get_admin_interface_languages(context)
-        self.assertEqual(languages, None)
+        with self.assertWarnsMessage(UserWarning, "django.conf.urls.i18n"):
+            tag_context = templatetags.admin_interface_language_chooser(context)
+        self.assertEqual(tag_context, None)
+
+    @override_settings(
+        MIDDLEWARE=[],
+    )
+    def test_admin_interface_language_chooser_without_locale_middleware(self):
+        context = Context({"request": self.request_factory.get("/en/admin/")})
+        with self.assertWarnsMessage(UserWarning, "LocaleMiddleware"):
+            tag_context = templatetags.admin_interface_language_chooser(context)
+        self.assertEqual(tag_context, None)
 
     @override_settings(
         LANGUAGES=(("en", "English"),),
     )
-    def test_get_admin_interface_languages_without_multiple_languages(self):
+    def test_admin_interface_language_chooser_without_multiple_languages(self):
         context = Context({"request": self.request_factory.get("/en/admin/")})
-        languages = templatetags.get_admin_interface_languages(context)
-        self.assertEqual(languages, None)
+        tag_context = templatetags.admin_interface_language_chooser(context)
+        self.assertEqual(tag_context, None)
 
-    def test_get_admin_interface_languages_without_request(self):
+    def test_admin_interface_language_chooser_without_request(self):
         context = Context({})
-        languages = templatetags.get_admin_interface_languages(context)
-        self.assertEqual(languages, None)
+        tag_context = templatetags.admin_interface_language_chooser(context)
+        self.assertEqual(tag_context, None)
 
-    def test_get_admin_interface_languages_without_language_prefix_in_url(self):
+    def test_admin_interface_language_chooser_without_language_prefix_in_url(self):
         context = Context({"request": self.request_factory.get("/admin/")})
-        languages = templatetags.get_admin_interface_languages(context)
-        self.assertEqual(languages, None)
+        tag_context = templatetags.admin_interface_language_chooser(context)
+        self.assertEqual(tag_context["next"], "/admin/")
 
     def test_get_theme(self):
         Theme.objects.all().delete()