Refs #1873 -- Used GET.lists() in admin filters.

3 files changed, 35 insertions, 18 deletions

diff --git a/django/contrib/admin/filters.py b/django/contrib/admin/filters.py
index 9e468dedd9..3ae7805dc2 100644
--- a/django/contrib/admin/filters.py
+++ b/django/contrib/admin/filters.py
@@ -9,6 +9,7 @@ import datetime
 
 from django.contrib.admin.options import IncorrectLookupParameters
 from django.contrib.admin.utils import (
+    get_last_value_from_parameters,
     get_model_from_relation,
     prepare_lookup_value,
     reverse_field_path,
@@ -98,7 +99,7 @@ class SimpleListFilter(FacetsMixin, ListFilter):
             )
         if self.parameter_name in params:
             value = params.pop(self.parameter_name)
-            self.used_parameters[self.parameter_name] = value
+            self.used_parameters[self.parameter_name] = value[-1]
         lookup_choices = self.lookups(request, model_admin)
         if lookup_choices is None:
             lookup_choices = ()
@@ -219,8 +220,10 @@ class RelatedFieldListFilter(FieldListFilter):
         other_model = get_model_from_relation(field)
         self.lookup_kwarg = "%s__%s__exact" % (field_path, field.target_field.name)
         self.lookup_kwarg_isnull = "%s__isnull" % field_path
-        self.lookup_val = params.get(self.lookup_kwarg)
-        self.lookup_val_isnull = params.get(self.lookup_kwarg_isnull)
+        self.lookup_val = get_last_value_from_parameters(params, self.lookup_kwarg)
+        self.lookup_val_isnull = get_last_value_from_parameters(
+            params, self.lookup_kwarg_isnull
+        )
         super().__init__(field, request, params, model, model_admin, field_path)
         self.lookup_choices = self.field_choices(field, request, model_admin)
         if hasattr(field, "verbose_name"):
@@ -317,8 +320,8 @@ class BooleanFieldListFilter(FieldListFilter):
     def __init__(self, field, request, params, model, model_admin, field_path):
         self.lookup_kwarg = "%s__exact" % field_path
         self.lookup_kwarg2 = "%s__isnull" % field_path
-        self.lookup_val = params.get(self.lookup_kwarg)
-        self.lookup_val2 = params.get(self.lookup_kwarg2)
+        self.lookup_val = get_last_value_from_parameters(params, self.lookup_kwarg)
+        self.lookup_val2 = get_last_value_from_parameters(params, self.lookup_kwarg2)
         super().__init__(field, request, params, model, model_admin, field_path)
         if (
             self.used_parameters
@@ -388,8 +391,10 @@ class ChoicesFieldListFilter(FieldListFilter):
     def __init__(self, field, request, params, model, model_admin, field_path):
         self.lookup_kwarg = "%s__exact" % field_path
         self.lookup_kwarg_isnull = "%s__isnull" % field_path
-        self.lookup_val = params.get(self.lookup_kwarg)
-        self.lookup_val_isnull = params.get(self.lookup_kwarg_isnull)
+        self.lookup_val = get_last_value_from_parameters(params, self.lookup_kwarg)
+        self.lookup_val_isnull = get_last_value_from_parameters(
+            params, self.lookup_kwarg_isnull
+        )
         super().__init__(field, request, params, model, model_admin, field_path)
 
     def expected_parameters(self):
@@ -450,7 +455,7 @@ class DateFieldListFilter(FieldListFilter):
     def __init__(self, field, request, params, model, model_admin, field_path):
         self.field_generic = "%s__" % field_path
         self.date_params = {
-            k: v for k, v in params.items() if k.startswith(self.field_generic)
+            k: v[-1] for k, v in params.items() if k.startswith(self.field_generic)
         }
 
         now = timezone.now()
@@ -550,8 +555,10 @@ class AllValuesFieldListFilter(FieldListFilter):
     def __init__(self, field, request, params, model, model_admin, field_path):
         self.lookup_kwarg = field_path
         self.lookup_kwarg_isnull = "%s__isnull" % field_path
-        self.lookup_val = params.get(self.lookup_kwarg)
-        self.lookup_val_isnull = params.get(self.lookup_kwarg_isnull)
+        self.lookup_val = get_last_value_from_parameters(params, self.lookup_kwarg)
+        self.lookup_val_isnull = get_last_value_from_parameters(
+            params, self.lookup_kwarg_isnull
+        )
         self.empty_value_display = model_admin.get_empty_value_display()
         parent_model, reverse_path = reverse_field_path(model, field_path)
         # Obey parent ModelAdmin queryset when deciding which options to show
@@ -646,7 +653,7 @@ class EmptyFieldListFilter(FieldListFilter):
                 )
             )
         self.lookup_kwarg = "%s__isempty" % field_path
-        self.lookup_val = params.get(self.lookup_kwarg)
+        self.lookup_val = get_last_value_from_parameters(params, self.lookup_kwarg)
         super().__init__(field, request, params, model, model_admin, field_path)
 
     def get_lookup_condition(self):
diff --git a/django/contrib/admin/utils.py b/django/contrib/admin/utils.py
index b971bd528f..90442788c9 100644
--- a/django/contrib/admin/utils.py
+++ b/django/contrib/admin/utils.py
@@ -54,10 +54,17 @@ def lookup_spawns_duplicates(opts, lookup_path):
     return False
 
 
+def get_last_value_from_parameters(parameters, key):
+    value = parameters.get(key)
+    return value[-1] if isinstance(value, list) else value
+
+
 def prepare_lookup_value(key, value, separator=","):
     """
     Return a lookup value prepared to be used in queryset filtering.
     """
+    if isinstance(value, list):
+        value = value[-1]
     # if key ends with __in, split parameter into separate values
     if key.endswith("__in"):
         value = value.split(separator)
diff --git a/django/contrib/admin/views/main.py b/django/contrib/admin/views/main.py
index 6d88dfc883..c0c03819f3 100644
--- a/django/contrib/admin/views/main.py
+++ b/django/contrib/admin/views/main.py
@@ -123,10 +123,13 @@ class ChangeList:
             )
         self.to_field = to_field
         self.params = dict(request.GET.items())
+        self.filter_params = dict(request.GET.lists())
         if PAGE_VAR in self.params:
             del self.params[PAGE_VAR]
+            del self.filter_params[PAGE_VAR]
         if ERROR_FLAG in self.params:
             del self.params[ERROR_FLAG]
+            del self.filter_params[ERROR_FLAG]
         self.remove_facet_link = self.get_query_string(remove=[IS_FACETS_VAR])
         self.add_facet_link = self.get_query_string({IS_FACETS_VAR: True})
 
@@ -156,7 +159,7 @@ class ChangeList:
         """
         Return all params except IGNORED_PARAMS.
         """
-        params = params or self.params
+        params = params or self.filter_params
         lookup_params = params.copy()  # a dictionary of the query string
         # Remove all the parameters that are globally and systematically
         # ignored.
@@ -171,7 +174,7 @@ class ChangeList:
         has_active_filters = False
 
         for key, value in lookup_params.items():
-            if not self.model_admin.lookup_allowed(key, value):
+            if not self.model_admin.lookup_allowed(key, value[-1]):
                 raise DisallowedModelAdminLookup("Filtering by %s not allowed" % key)
 
         filter_specs = []
@@ -224,9 +227,9 @@ class ChangeList:
                 day = lookup_params.pop("%s__day" % self.date_hierarchy, None)
                 try:
                     from_date = datetime(
-                        int(year),
-                        int(month if month is not None else 1),
-                        int(day if day is not None else 1),
+                        int(year[-1]),
+                        int(month[-1] if month is not None else 1),
+                        int(day[-1] if day is not None else 1),
                     )
                 except ValueError as e:
                     raise IncorrectLookupParameters(e) from e
@@ -273,7 +276,7 @@ class ChangeList:
             new_params = {}
         if remove is None:
             remove = []
-        p = self.params.copy()
+        p = self.filter_params.copy()
         for r in remove:
             for k in list(p):
                 if k.startswith(r):
@@ -284,7 +287,7 @@ class ChangeList:
                     del p[k]
             else:
                 p[k] = v
-        return "?%s" % urlencode(sorted(p.items()))
+        return "?%s" % urlencode(sorted(p.items()), doseq=True)
 
     def get_results(self, request):
         paginator = self.model_admin.get_paginator(