Fixed #36268 -- Added leading ? in every querystring template tag result.

Thanks Sarah Boyce for the report.

django/template/defaulttags.py

@@ -1182,6 +1182,8 @@ def querystring(context, query_dict=None, **kwargs):
     `request.GET`). Keyword arguments are processed sequentially, with later
     arguments taking precedence.
 
+    A query string prefixed with `?` is returned.
+
     For example::
 
         {# Set a parameter on top of `request.GET` #}
@@ -1207,9 +1209,7 @@ def querystring(context, query_dict=None, **kwargs):
             params.setlist(key, value)
         else:
             params[key] = value
-    if not params and not query_dict:
-        return ""
-    query_string = params.urlencode()
+    query_string = params.urlencode() if params else ""
     return f"?{query_string}"
 
 

docs/ref/templates/builtins.txt

@@ -967,9 +967,8 @@ Outputs a URL-encoded formatted query string based on the provided parameters.
 This tag requires a :class:`~django.http.QueryDict` instance, which defaults to
 :attr:`request.GET <django.http.HttpRequest.GET>` if none is provided.
 
-If the :class:`~django.http.QueryDict` is empty and no additional parameters
-are provided, an empty string is returned. Otherwise, the result includes a
-leading ``"?"``.
+The result always includes a leading ``"?"`` since this tag is mainly used for
+links, and an empty result could prevent the page from reloading as expected.
 
 .. admonition:: Using ``request.GET`` as default
 
@@ -979,6 +978,10 @@ leading ``"?"``.
     ``request`` object into the template context, or provide a ``QueryDict``
     instance to this tag.
 
+.. versionchanged:: 6.0
+
+    A ``?`` was prepended to the query string for empty results.
+
 Basic usage
 ~~~~~~~~~~~
 
@@ -986,8 +989,9 @@ Basic usage
 
     {% querystring %}
 
-Outputs the current query string verbatim. So if the query string is
-``?color=green``, the output would be ``?color=green``.
+Outputs the current query string verbatim. So if the query string in the
+request is ``?color=green``, the output would be ``?color=green``. If the
+current query string is empty, the output will be ``?``.
 
 .. code-block:: html+django
 
@@ -1038,7 +1042,7 @@ Custom QueryDict
 
 You can provide a custom ``QueryDict`` to be used instead of ``request.GET``.
 So if ``my_query_dict`` is ``<QueryDict: {'color': ['blue']}>``, this outputs
-``?color=blue``.
+``?color=blue``. If ``my_query_dict`` is empty, the output will be ``?``.
 
 Dynamic usage
 ~~~~~~~~~~~~~

docs/releases/6.0.txt

@@ -233,6 +233,9 @@ Templates
 * The new variable ``forloop.length`` is now available within a :ttag:`for`
   loop.
 
+* The :ttag:`querystring` template tag now consistently prefixes the returned
+  query string with a ``?``, ensuring reliable link generation behavior.
+
 Tests
 ~~~~~
 

tests/template_tests/syntax_tests/test_querystring.py

@@ -16,17 +16,15 @@ class QueryStringTagTests(SimpleTestCase):
     @setup({"querystring_empty_get_params": "{% querystring %}"})
     def test_querystring_empty_get_params(self):
         context = RequestContext(self.request_factory.get("/"))
-        self.assertRenderEqual("querystring_empty_get_params", context, expected="")
+        self.assertRenderEqual("querystring_empty_get_params", context, expected="?")
 
     @setup({"querystring_remove_all_params": "{% querystring a=None %}"})
     def test_querystring_remove_all_params(self):
         non_empty_context = RequestContext(self.request_factory.get("/?a=b"))
         empty_context = RequestContext(self.request_factory.get("/"))
-        for context, expected in [(non_empty_context, "?"), (empty_context, "")]:
-            with self.subTest(expected=expected):
-                self.assertRenderEqual(
-                    "querystring_remove_all_params", context, expected
-                )
+        for context in [non_empty_context, empty_context]:
+            with self.subTest(context=context):
+                self.assertRenderEqual("querystring_remove_all_params", context, "?")
 
     @setup({"querystring_non_empty_get_params": "{% querystring %}"})
     def test_querystring_non_empty_get_params(self):
@@ -46,10 +44,20 @@ class QueryStringTagTests(SimpleTestCase):
     def test_querystring_empty_params(self):
         cases = [None, {}, QueryDict()]
         request = self.request_factory.get("/")
+        qs = "?a=b"
+        request_with_qs = self.request_factory.get(f"/{qs}")
         for param in cases:
+            # Empty `query_dict` and nothing on `request.GET`.
             with self.subTest(param=param):
                 context = RequestContext(request, {"qd": param})
-                self.assertRenderEqual("querystring_empty_params", context, expected="")
+                self.assertRenderEqual(
+                    "querystring_empty_params", context, expected="?"
+                )
+            # Empty `query_dict` and a query string in `request.GET`.
+            with self.subTest(param=param, qs=qs):
+                context = RequestContext(request_with_qs, {"qd": param})
+                expected = "?" if param is not None else qs
+                self.assertRenderEqual("querystring_empty_params", context, expected)
 
     @setup({"querystring_replace": "{% querystring a=1 %}"})
     def test_querystring_replace(self):