Fixed #31026 -- Switched form rendering to template engine.

Thanks Carlton Gibson, Keryn Knight, Mariusz Felisiak, and Nick Pope
for reviews.

Co-authored-by: Johannes Hoppe <info@johanneshoppe.com>

8 files changed, 293 insertions, 137 deletions

diff --git a/tests/forms_tests/templates/forms_tests/error.html b/tests/forms_tests/templates/forms_tests/error.html
new file mode 100644
index 0000000000..4981d32b70
--- /dev/null
+++ b/tests/forms_tests/templates/forms_tests/error.html
@@ -0,0 +1 @@
+{% if errors %}<div class="errorlist">{% for error in errors %}<div class="error">{{ error }}</div>{% endfor %}</div>{% endif %}
diff --git a/tests/forms_tests/templates/forms_tests/form_snippet.html b/tests/forms_tests/templates/forms_tests/form_snippet.html
new file mode 100644
index 0000000000..90ab4f2981
--- /dev/null
+++ b/tests/forms_tests/templates/forms_tests/form_snippet.html
@@ -0,0 +1,6 @@
+{% for field in form %}
+  <div class="fieldWrapper">
+    {{ field.errors }}
+    {{ field.label_tag }} {{ field }}
+  </div>
+{% endfor %}
diff --git a/tests/forms_tests/tests/__init__.py b/tests/forms_tests/tests/__init__.py
index e69de29bb2..7fc0269ec5 100644
--- a/tests/forms_tests/tests/__init__.py
+++ b/tests/forms_tests/tests/__init__.py
@@ -0,0 +1,30 @@
+import inspect
+
+from django.test.utils import override_settings
+
+TEST_SETTINGS = [
+    {
+        'FORM_RENDERER': 'django.forms.renderers.DjangoTemplates',
+        'TEMPLATES': {'BACKEND': 'django.template.backends.django.DjangoTemplates'},
+    },
+    {
+        'FORM_RENDERER': 'django.forms.renderers.Jinja2',
+        'TEMPLATES': {'BACKEND': 'django.template.backends.jinja2.Jinja2'},
+    },
+]
+
+
+def test_all_form_renderers():
+    def wrapper(func):
+        def inner(*args, **kwargs):
+            for settings in TEST_SETTINGS:
+                with override_settings(**settings):
+                    func(*args, **kwargs)
+        return inner
+
+    def decorator(cls):
+        for name, func in inspect.getmembers(cls, inspect.isfunction):
+            if name.startswith('test_'):
+                setattr(cls, name, wrapper(func))
+        return cls
+    return decorator
diff --git a/tests/forms_tests/tests/test_deprecation_forms.py b/tests/forms_tests/tests/test_deprecation_forms.py
new file mode 100644
index 0000000000..6bdb595602
--- /dev/null
+++ b/tests/forms_tests/tests/test_deprecation_forms.py
@@ -0,0 +1,183 @@
+# RemovedInDjango50
+from django.forms import CharField, EmailField, Form, HiddenInput
+from django.forms.utils import ErrorList
+from django.test import SimpleTestCase, ignore_warnings
+from django.utils.deprecation import RemovedInDjango50Warning
+
+from .test_forms import Person
+
+
+class DivErrorList(ErrorList):
+    def __str__(self):
+        return self.as_divs()
+
+    def as_divs(self):
+        if not self:
+            return ''
+        return '<div class="errorlist">%s</div>' % ''.join(
+            f'<div class="error">{error}</div>' for error in self
+        )
+
+
+class DeprecationTests(SimpleTestCase):
+    def test_deprecation_warning_html_output(self):
+        msg = (
+            'django.forms.BaseForm._html_output() is deprecated. Please use '
+            '.render() and .get_context() instead.'
+        )
+        with self.assertRaisesMessage(RemovedInDjango50Warning, msg):
+            form = Person()
+            form._html_output(
+                normal_row='<p id="p_%(field_name)s"></p>',
+                error_row='%s',
+                row_ender='</p>',
+                help_text_html=' %s',
+                errors_on_separate_row=True,
+            )
+
+    def test_deprecation_warning_error_list(self):
+        class EmailForm(Form):
+            email = EmailField()
+            comment = CharField()
+
+        data = {'email': 'invalid'}
+        f = EmailForm(data, error_class=DivErrorList)
+        msg = (
+            'Returning a plain string from DivErrorList is deprecated. Please '
+            'customize via the template system instead.'
+        )
+        with self.assertRaisesMessage(RemovedInDjango50Warning, msg):
+            f.as_p()
+
+
+@ignore_warnings(category=RemovedInDjango50Warning)
+class DeprecatedTests(SimpleTestCase):
+    def test_errorlist_override_str(self):
+        class CommentForm(Form):
+            name = CharField(max_length=50, required=False)
+            email = EmailField()
+            comment = CharField()
+
+        data = {'email': 'invalid'}
+        f = CommentForm(data, auto_id=False, error_class=DivErrorList)
+        self.assertHTMLEqual(
+            f.as_p(),
+            '<p>Name: <input type="text" name="name" maxlength="50"></p>'
+            '<div class="errorlist">'
+            '<div class="error">Enter a valid email address.</div></div>'
+            '<p>Email: <input type="email" name="email" value="invalid" required></p>'
+            '<div class="errorlist">'
+            '<div class="error">This field is required.</div></div>'
+            '<p>Comment: <input type="text" name="comment" required></p>',
+        )
+
+    def test_field_name(self):
+        """#5749 - `field_name` may be used as a key in _html_output()."""
+        class SomeForm(Form):
+            some_field = CharField()
+
+            def as_p(self):
+                return self._html_output(
+                    normal_row='<p id="p_%(field_name)s"></p>',
+                    error_row='%s',
+                    row_ender='</p>',
+                    help_text_html=' %s',
+                    errors_on_separate_row=True,
+                )
+
+        form = SomeForm()
+        self.assertHTMLEqual(form.as_p(), '<p id="p_some_field"></p>')
+
+    def test_field_without_css_classes(self):
+        """
+        `css_classes` may be used as a key in _html_output() (empty classes).
+        """
+        class SomeForm(Form):
+            some_field = CharField()
+
+            def as_p(self):
+                return self._html_output(
+                    normal_row='<p class="%(css_classes)s"></p>',
+                    error_row='%s',
+                    row_ender='</p>',
+                    help_text_html=' %s',
+                    errors_on_separate_row=True,
+                )
+
+        form = SomeForm()
+        self.assertHTMLEqual(form.as_p(), '<p class=""></p>')
+
+    def test_field_with_css_class(self):
+        """
+        `css_classes` may be used as a key in _html_output() (class comes
+        from required_css_class in this case).
+        """
+        class SomeForm(Form):
+            some_field = CharField()
+            required_css_class = 'foo'
+
+            def as_p(self):
+                return self._html_output(
+                    normal_row='<p class="%(css_classes)s"></p>',
+                    error_row='%s',
+                    row_ender='</p>',
+                    help_text_html=' %s',
+                    errors_on_separate_row=True,
+                )
+
+        form = SomeForm()
+        self.assertHTMLEqual(form.as_p(), '<p class="foo"></p>')
+
+    def test_field_name_with_hidden_input(self):
+        """
+        BaseForm._html_output() should merge all the hidden input fields and
+        put them in the last row.
+        """
+        class SomeForm(Form):
+            hidden1 = CharField(widget=HiddenInput)
+            custom = CharField()
+            hidden2 = CharField(widget=HiddenInput)
+
+            def as_p(self):
+                return self._html_output(
+                    normal_row='<p%(html_class_attr)s>%(field)s %(field_name)s</p>',
+                    error_row='%s',
+                    row_ender='</p>',
+                    help_text_html=' %s',
+                    errors_on_separate_row=True,
+                )
+
+        form = SomeForm()
+        self.assertHTMLEqual(
+            form.as_p(),
+            '<p><input id="id_custom" name="custom" type="text" required> custom'
+            '<input id="id_hidden1" name="hidden1" type="hidden">'
+            '<input id="id_hidden2" name="hidden2" type="hidden"></p>'
+        )
+
+    def test_field_name_with_hidden_input_and_non_matching_row_ender(self):
+        """
+        BaseForm._html_output() should merge all the hidden input fields and
+        put them in the last row ended with the specific row ender.
+        """
+        class SomeForm(Form):
+            hidden1 = CharField(widget=HiddenInput)
+            custom = CharField()
+            hidden2 = CharField(widget=HiddenInput)
+
+            def as_p(self):
+                return self._html_output(
+                    normal_row='<p%(html_class_attr)s>%(field)s %(field_name)s</p>',
+                    error_row='%s',
+                    row_ender='<hr><hr>',
+                    help_text_html=' %s',
+                    errors_on_separate_row=True,
+                )
+
+        form = SomeForm()
+        self.assertHTMLEqual(
+            form.as_p(),
+            '<p><input id="id_custom" name="custom" type="text" required> custom</p>\n'
+            '<input id="id_hidden1" name="hidden1" type="hidden">'
+            '<input id="id_hidden2" name="hidden2" type="hidden"><hr><hr>'
+        )
diff --git a/tests/forms_tests/tests/test_forms.py b/tests/forms_tests/tests/test_forms.py
index b713cb1321..8c08cd5ad4 100644
--- a/tests/forms_tests/tests/test_forms.py
+++ b/tests/forms_tests/tests/test_forms.py
@@ -23,6 +23,7 @@ from django.test import SimpleTestCase
 from django.test.utils import override_settings
 from django.utils.datastructures import MultiValueDict
 from django.utils.safestring import mark_safe
+from tests.forms_tests.tests import test_all_form_renderers
 
 
 class FrameworkForm(Form):
@@ -55,6 +56,7 @@ class MultiValueDictLike(dict):
         return [self[key]]
 
 
+@test_all_form_renderers()
 class FormsTestCase(SimpleTestCase):
     # A Form is a collection of Fields. It knows how to validate a set of data and it
     # knows how to render itself in a couple of default ways (e.g., an HTML table).
@@ -3077,117 +3079,6 @@ Password: <input type="password" name="password" required>
 
         self.assertHTMLEqual(boundfield.label_tag(label_suffix='$'), '<label for="id_field">Field$</label>')
 
-    def test_field_name(self):
-        """#5749 - `field_name` may be used as a key in _html_output()."""
-        class SomeForm(Form):
-            some_field = CharField()
-
-            def as_p(self):
-                return self._html_output(
-                    normal_row='<p id="p_%(field_name)s"></p>',
-                    error_row='%s',
-                    row_ender='</p>',
-                    help_text_html=' %s',
-                    errors_on_separate_row=True,
-                )
-
-        form = SomeForm()
-        self.assertHTMLEqual(form.as_p(), '<p id="p_some_field"></p>')
-
-    def test_field_without_css_classes(self):
-        """
-        `css_classes` may be used as a key in _html_output() (empty classes).
-        """
-        class SomeForm(Form):
-            some_field = CharField()
-
-            def as_p(self):
-                return self._html_output(
-                    normal_row='<p class="%(css_classes)s"></p>',
-                    error_row='%s',
-                    row_ender='</p>',
-                    help_text_html=' %s',
-                    errors_on_separate_row=True,
-                )
-
-        form = SomeForm()
-        self.assertHTMLEqual(form.as_p(), '<p class=""></p>')
-
-    def test_field_with_css_class(self):
-        """
-        `css_classes` may be used as a key in _html_output() (class comes
-        from required_css_class in this case).
-        """
-        class SomeForm(Form):
-            some_field = CharField()
-            required_css_class = 'foo'
-
-            def as_p(self):
-                return self._html_output(
-                    normal_row='<p class="%(css_classes)s"></p>',
-                    error_row='%s',
-                    row_ender='</p>',
-                    help_text_html=' %s',
-                    errors_on_separate_row=True,
-                )
-
-        form = SomeForm()
-        self.assertHTMLEqual(form.as_p(), '<p class="foo"></p>')
-
-    def test_field_name_with_hidden_input(self):
-        """
-        BaseForm._html_output() should merge all the hidden input fields and
-        put them in the last row.
-        """
-        class SomeForm(Form):
-            hidden1 = CharField(widget=HiddenInput)
-            custom = CharField()
-            hidden2 = CharField(widget=HiddenInput)
-
-            def as_p(self):
-                return self._html_output(
-                    normal_row='<p%(html_class_attr)s>%(field)s %(field_name)s</p>',
-                    error_row='%s',
-                    row_ender='</p>',
-                    help_text_html=' %s',
-                    errors_on_separate_row=True,
-                )
-
-        form = SomeForm()
-        self.assertHTMLEqual(
-            form.as_p(),
-            '<p><input id="id_custom" name="custom" type="text" required> custom'
-            '<input id="id_hidden1" name="hidden1" type="hidden">'
-            '<input id="id_hidden2" name="hidden2" type="hidden"></p>'
-        )
-
-    def test_field_name_with_hidden_input_and_non_matching_row_ender(self):
-        """
-        BaseForm._html_output() should merge all the hidden input fields and
-        put them in the last row ended with the specific row ender.
-        """
-        class SomeForm(Form):
-            hidden1 = CharField(widget=HiddenInput)
-            custom = CharField()
-            hidden2 = CharField(widget=HiddenInput)
-
-            def as_p(self):
-                return self._html_output(
-                    normal_row='<p%(html_class_attr)s>%(field)s %(field_name)s</p>',
-                    error_row='%s',
-                    row_ender='<hr><hr>',
-                    help_text_html=' %s',
-                    errors_on_separate_row=True
-                )
-
-        form = SomeForm()
-        self.assertHTMLEqual(
-            form.as_p(),
-            '<p><input id="id_custom" name="custom" type="text" required> custom</p>\n'
-            '<input id="id_hidden1" name="hidden1" type="hidden">'
-            '<input id="id_hidden2" name="hidden2" type="hidden"><hr><hr>'
-        )
-
     def test_error_dict(self):
         class MyForm(Form):
             foo = CharField()
@@ -3377,30 +3268,6 @@ Password: <input type="password" name="password" required>
 <input id="id_last_name" name="last_name" type="text" value="Lennon" required></td></tr>"""
         )
 
-    def test_errorlist_override(self):
-        class DivErrorList(ErrorList):
-            def __str__(self):
-                return self.as_divs()
-
-            def as_divs(self):
-                if not self:
-                    return ''
-                return '<div class="errorlist">%s</div>' % ''.join(
-                    '<div class="error">%s</div>' % e for e in self)
-
-        class CommentForm(Form):
-            name = CharField(max_length=50, required=False)
-            email = EmailField()
-            comment = CharField()
-
-        data = {'email': 'invalid'}
-        f = CommentForm(data, auto_id=False, error_class=DivErrorList)
-        self.assertHTMLEqual(f.as_p(), """<p>Name: <input type="text" name="name" maxlength="50"></p>
-<div class="errorlist"><div class="error">Enter a valid email address.</div></div>
-<p>Email: <input type="email" name="email" value="invalid" required></p>
-<div class="errorlist"><div class="error">This field is required.</div></div>
-<p>Comment: <input type="text" name="comment" required></p>""")
-
     def test_error_escaping(self):
         class TestForm(Form):
             hidden = CharField(widget=HiddenInput(), required=False)
@@ -4045,3 +3912,40 @@ class TemplateTests(SimpleTestCase):
             "VALID: [('password1', 'secret'), ('password2', 'secret'), "
             "('username', 'adrian')]",
         )
+
+
+class OverrideTests(SimpleTestCase):
+    def test_use_custom_template(self):
+        class Person(Form):
+            first_name = CharField()
+            template_name = 'forms_tests/form_snippet.html'
+
+        t = Template('{{ form }}')
+        html = t.render(Context({'form': Person()}))
+        expected = """
+        <div class="fieldWrapper"><label for="id_first_name">First name:</label>
+        <input type="text" name="first_name" required id="id_first_name"></div>
+        """
+        self.assertHTMLEqual(html, expected)
+
+    def test_errorlist_override(self):
+        class CustomErrorList(ErrorList):
+            template_name = 'forms_tests/error.html'
+
+        class CommentForm(Form):
+            name = CharField(max_length=50, required=False)
+            email = EmailField()
+            comment = CharField()
+
+        data = {'email': 'invalid'}
+        f = CommentForm(data, auto_id=False, error_class=CustomErrorList)
+        self.assertHTMLEqual(
+            f.as_p(),
+            '<p>Name: <input type="text" name="name" maxlength="50"></p>'
+            '<div class="errorlist">'
+            '<div class="error">Enter a valid email address.</div></div>'
+            '<p>Email: <input type="email" name="email" value="invalid" required></p>'
+            '<div class="errorlist">'
+            '<div class="error">This field is required.</div></div>'
+            '<p>Comment: <input type="text" name="comment" required></p>',
+        )
diff --git a/tests/forms_tests/tests/test_formsets.py b/tests/forms_tests/tests/test_formsets.py
index 06b61306fe..0d7d452d71 100644
--- a/tests/forms_tests/tests/test_formsets.py
+++ b/tests/forms_tests/tests/test_formsets.py
@@ -11,6 +11,7 @@ from django.forms.formsets import BaseFormSet, all_valid, formset_factory
 from django.forms.utils import ErrorList
 from django.forms.widgets import HiddenInput
 from django.test import SimpleTestCase
+from tests.forms_tests.tests import test_all_form_renderers
 
 
 class Choice(Form):
@@ -47,6 +48,7 @@ class CustomKwargForm(Form):
         super().__init__(*args, **kwargs)
 
 
+@test_all_form_renderers()
 class FormsFormsetTestCase(SimpleTestCase):
 
     def make_choiceformset(
@@ -1288,7 +1290,32 @@ class FormsFormsetTestCase(SimpleTestCase):
         self.assertIs(formset._should_delete_form(formset.forms[1]), False)
         self.assertIs(formset._should_delete_form(formset.forms[2]), False)
 
+    def test_custom_renderer(self):
+        """
+        A custom renderer passed to a formset_factory() is passed to all forms
+        and ErrorList.
+        """
+        from django.forms.renderers import Jinja2
+        renderer = Jinja2()
+        data = {
+            'choices-TOTAL_FORMS': '2',
+            'choices-INITIAL_FORMS': '0',
+            'choices-MIN_NUM_FORMS': '0',
+            'choices-0-choice': 'Zero',
+            'choices-0-votes': '',
+            'choices-1-choice': 'One',
+            'choices-1-votes': '',
+        }
+        ChoiceFormSet = formset_factory(Choice, renderer=renderer)
+        formset = ChoiceFormSet(data, auto_id=False, prefix='choices')
+        self.assertEqual(formset.renderer, renderer)
+        self.assertEqual(formset.forms[0].renderer, renderer)
+        self.assertEqual(formset.management_form.renderer, renderer)
+        self.assertEqual(formset.non_form_errors().renderer, renderer)
+        self.assertEqual(formset.empty_form.renderer, renderer)
+
 
+@test_all_form_renderers()
 class FormsetAsTagTests(SimpleTestCase):
     def setUp(self):
         data = {
@@ -1345,6 +1372,7 @@ class ArticleForm(Form):
 ArticleFormSet = formset_factory(ArticleForm)
 
 
+@test_all_form_renderers()
 class TestIsBoundBehavior(SimpleTestCase):
     def test_no_data_error(self):
         formset = ArticleFormSet({})
@@ -1359,7 +1387,7 @@ class TestIsBoundBehavior(SimpleTestCase):
         )
         self.assertEqual(formset.errors, [])
         # Can still render the formset.
-        self.assertEqual(
+        self.assertHTMLEqual(
             str(formset),
             '<tr><td colspan="2">'
             '<ul class="errorlist nonfield">'
@@ -1390,7 +1418,7 @@ class TestIsBoundBehavior(SimpleTestCase):
         )
         self.assertEqual(formset.errors, [])
         # Can still render the formset.
-        self.assertEqual(
+        self.assertHTMLEqual(
             str(formset),
             '<tr><td colspan="2">'
             '<ul class="errorlist nonfield">'
diff --git a/tests/forms_tests/tests/test_i18n.py b/tests/forms_tests/tests/test_i18n.py
index d941902af2..fc5d59c480 100644
--- a/tests/forms_tests/tests/test_i18n.py
+++ b/tests/forms_tests/tests/test_i18n.py
@@ -4,8 +4,10 @@ from django.forms import (
 from django.test import SimpleTestCase
 from django.utils import translation
 from django.utils.translation import gettext_lazy
+from tests.forms_tests.tests import test_all_form_renderers
 
 
+@test_all_form_renderers()
 class FormsI18nTests(SimpleTestCase):
     def test_lazy_labels(self):
         class SomeForm(Form):
diff --git a/tests/forms_tests/tests/tests.py b/tests/forms_tests/tests/tests.py
index 18b4c58b5e..ec08a5f9ef 100644
--- a/tests/forms_tests/tests/tests.py
+++ b/tests/forms_tests/tests/tests.py
@@ -5,6 +5,7 @@ from django.db import models
 from django.forms import CharField, FileField, Form, ModelForm
 from django.forms.models import ModelFormMetaclass
 from django.test import SimpleTestCase, TestCase
+from tests.forms_tests.tests import test_all_form_renderers
 
 from ..models import (
     BoundaryModel, ChoiceFieldModel, ChoiceModel, ChoiceOptionModel, Defaults,
@@ -283,6 +284,7 @@ class ManyToManyExclusionTestCase(TestCase):
         self.assertEqual([obj.pk for obj in form.instance.multi_choice_int.all()], data['multi_choice_int'])
 
 
+@test_all_form_renderers()
 class EmptyLabelTestCase(TestCase):
     def test_empty_field_char(self):
         f = EmptyCharLabelChoiceForm()