templatetags: add |startswith:"..." (#38897)

combo/public/templatetags/combo.py

@@ -28,6 +28,7 @@ from django.template import VariableDoesNotExist
 from django.template.base import TOKEN_BLOCK, TOKEN_VAR, TOKEN_COMMENT
 from django.template.defaultfilters import stringfilter
 from django.utils import dateparse
+from django.utils.encoding import force_text
 
 from combo.data.models import Page, Placeholder
 from combo.public.menu import get_menu_context
@@ -264,3 +265,7 @@ def name_id(user):
 @register.simple_tag
 def get_page(page_slug):
     return Page.objects.get(slug=page_slug)
+
+@register.filter
+def startswith(string, substring):
+    return string and force_text(string).startswith(force_text(substring))

tests/test_public_templatetags.py

@@ -192,3 +192,12 @@ def test_asset_template_tags():
         page.save()
         t = Template('''{% load assets %}{% asset_url page.picture "collectivity:banner" size="200x200" %}''')
         assert t.render(Context({'page': page})) == '/media/page-pictures/test2.svg'
+
+def test_startswith():
+    t = Template('{% if foo|startswith:"bar" %}ok{% endif %}')
+    context = Context({'foo': None})
+    assert t.render(context) == ''
+    context = Context({'foo': 'xx'})
+    assert t.render(context) == ''
+    context = Context({'foo': 'bar'})
+    assert t.render(context) == 'ok'