[1.11.x] Fixed #31073 -- Prevented CheckboxInput.get_context() from mutating attrs.

Backport of 02eff7ef60466da108b1a33f1e4dc01eec45c99d from master.

3 files changed, 18 insertions, 0 deletions

diff --git a/django/forms/widgets.py b/django/forms/widgets.py
index 2b7e07bea3..5e82c06213 100644
--- a/django/forms/widgets.py
+++ b/django/forms/widgets.py
@@ -508,6 +508,8 @@ class CheckboxInput(Input):
         if self.check_test(value):
             if attrs is None:
                 attrs = {}
+            else:
+                attrs = attrs.copy()
             attrs['checked'] = True
         return super(CheckboxInput, self).get_context(name, value, attrs)
 
diff --git a/tests/forms_tests/widget_tests/test_checkboxinput.py b/tests/forms_tests/widget_tests/test_checkboxinput.py
index 1ae6ab73b6..37bb2df552 100644
--- a/tests/forms_tests/widget_tests/test_checkboxinput.py
+++ b/tests/forms_tests/widget_tests/test_checkboxinput.py
@@ -89,3 +89,8 @@ class CheckboxInputTest(WidgetTest):
     def test_value_omitted_from_data(self):
         self.assertIs(self.widget.value_omitted_from_data({'field': 'value'}, {}, 'field'), False)
         self.assertIs(self.widget.value_omitted_from_data({}, {}, 'field'), False)
+
+    def test_get_context_does_not_mutate_attrs(self):
+        attrs = {'checked': False}
+        self.widget.get_context('name', True, attrs)
+        self.assertIs(attrs['checked'], False)
diff --git a/tests/postgres_tests/test_array.py b/tests/postgres_tests/test_array.py
index a66c92a016..0b706e85ad 100644
--- a/tests/postgres_tests/test_array.py
+++ b/tests/postgres_tests/test_array.py
@@ -826,6 +826,17 @@ class TestSplitFormWidget(PostgreSQLWidgetTestCase):
             }
         )
 
+    def test_checkbox_get_context_attrs(self):
+        context = SplitArrayWidget(
+            forms.CheckboxInput(),
+            size=2,
+        ).get_context('name', [True, False])
+        self.assertEqual(context['widget']['value'], '[True, False]')
+        self.assertEqual(
+            [subwidget['attrs'] for subwidget in context['widget']['subwidgets']],
+            [{'checked': True}, {}]
+        )
+
     def test_render(self):
         self.check_html(
             SplitArrayWidget(forms.TextInput(), size=2), 'array', None,