[3.0.x] Fixed #31012 -- Reverted "Fixed #29056 -- Fixed HTML5 validation of required SelectDateWidget."

This reverts commit f038214d91.

The initial issue was incorrect. Django 2.2, and before, did not
generate invalid HTML as reported. With f03821 in place invalid HTML
was generated.

Thanks to Kevin Brown for follow-up report and investigation.
Backport of ee4a19053a from master

django/forms/widgets.py

@@ -979,11 +979,7 @@ class SelectDateWidget(Widget):
         date_context['year'] = self.select_widget(attrs, choices=year_choices).get_context(
             name=year_name,
             value=context['widget']['value']['year'],
-            attrs={
+            attrs={**context['widget']['attrs'], 'id': 'id_%s' % year_name},
-                **context['widget']['attrs'],
-                'id': 'id_%s' % year_name,
-                'placeholder': _('Year') if self.is_required else False,
-            },
         )
         month_choices = list(self.months.items())
         if not self.is_required:
@@ -992,11 +988,7 @@ class SelectDateWidget(Widget):
         date_context['month'] = self.select_widget(attrs, choices=month_choices).get_context(
             name=month_name,
             value=context['widget']['value']['month'],
-            attrs={
+            attrs={**context['widget']['attrs'], 'id': 'id_%s' % month_name},
-                **context['widget']['attrs'],
-                'id': 'id_%s' % month_name,
-                'placeholder': _('Month') if self.is_required else False,
-            },
         )
         day_choices = [(i, i) for i in range(1, 32)]
         if not self.is_required:
@@ -1005,11 +997,7 @@ class SelectDateWidget(Widget):
         date_context['day'] = self.select_widget(attrs, choices=day_choices,).get_context(
             name=day_name,
             value=context['widget']['value']['day'],
-            attrs={
+            attrs={**context['widget']['attrs'], 'id': 'id_%s' % day_name},
-                **context['widget']['attrs'],
-                'id': 'id_%s' % day_name,
-                'placeholder': _('Day') if self.is_required else False,
-            },
         )
         subwidgets = []
         for field in self._parse_date_fmt():

docs/releases/3.0.txt

@@ -524,10 +524,6 @@ Miscellaneous
 
 * Support for ``pywatchman`` < 1.2.0 is removed.
 
-* HTML rendered by :class:`~django.forms.SelectDateWidget` for required fields
-  now have the ``placeholder`` attribute, which, mainly, may require some
-  adjustments in tests that compare HTML.
-
 * :func:`~django.utils.http.urlencode` now encodes iterable values as they are
   when ``doseq=False``, rather than iterating them, bringing it into line with
   the standard library :func:`urllib.parse.urlencode` function.

tests/forms_tests/widget_tests/test_selectdatewidget.py

@@ -314,46 +314,6 @@ class SelectDateWidgetTest(WidgetTest):
         self.assertFalse(GetNotRequiredDate().fields['mydate'].widget.is_required)
         self.assertTrue(GetRequiredDate().fields['mydate'].widget.is_required)
 
-    def test_selectdate_required_placeholder(self):
-        for required in (True, False):
-            field = DateField(widget=SelectDateWidget(years=('2018', '2019')), required=required)
-            self.check_html(field.widget, 'my_date', '', html=(
-                """
-                <select name="my_date_month" id="id_my_date_month" %(m_placeholder)s>
-                    %(empty)s
-                    <option value="1">January</option>
-                    <option value="2">February</option>
-                    <option value="3">March</option>
-                    <option value="4">April</option>
-                    <option value="5">May</option>
-                    <option value="6">June</option>
-                    <option value="7">July</option>
-                    <option value="8">August</option>
-                    <option value="9">September</option>
-                    <option value="10">October</option>
-                    <option value="11">November</option>
-                    <option value="12">December</option>
-                </select>
-                <select name="my_date_day" id="id_my_date_day" %(d_placeholder)s>
-                    %(empty)s
-                    %(days_options)s
-                </select>
-                <select name="my_date_year" id="id_my_date_year" %(y_placeholder)s>
-                    %(empty)s
-                    <option value="2018">2018</option>
-                    <option value="2019">2019</option>
-                </select>
-                """ % {
-                    'days_options': '\n'.join(
-                        '<option value="%s">%s</option>' % (i, i) for i in range(1, 32)
-                    ),
-                    'm_placeholder': 'placeholder="Month"' if required else '',
-                    'd_placeholder': 'placeholder="Day"' if required else '',
-                    'y_placeholder': 'placeholder="Year"' if required else '',
-                    'empty': '' if required else '<option selected value="">---</option>',
-                }
-            ))
-
     def test_selectdate_empty_label(self):
         w = SelectDateWidget(years=('2014',), empty_label='empty_label')