misc: add startswith templatetag (#25972)

tests/test_templates.py

@@ -67,6 +67,12 @@ def test_template_templatetag():
     tmpl = Template('{% load i18n %}{% trans "hello" %}')
     assert tmpl.render() == 'hello'
 
+def test_startswith_templatetag():
+    tmpl = Template('{% if foo|startswith:"bar" %}hello{% endif %}')
+    assert tmpl.render() == ''
+    assert tmpl.render({'foo': 'bar-baz'}) == 'hello'
+    assert tmpl.render({'foo': 'baz-bar'}) == ''
+
 def test_template_encoding():
     # django
     tmpl = Template('{{ foo }} à vélo')

wcs/qommon/templatetags/qommon.py

@@ -27,6 +27,10 @@ register = template.Library()
 def get(mapping, key):
     return mapping.get(key)
 
+@register.filter
+def startswith(string, substring):
+    return string and string.startswith(substring)
+
 @register.filter
 def parse_date(date_string):
     try: