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

This reverts commit f038214d917c982613f5a15db8dfe325b1f7479b.

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 ee4a19053a32d41cdd79e087b1968980804ce658 from master

3 files changed, 3 insertions, 59 deletions

diff --git a/django/forms/widgets.py b/django/forms/widgets.py
index f9627f2918..ba8346ac97 100644
--- a/django/forms/widgets.py
+++ b/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={
-                **context['widget']['attrs'],
-                'id': 'id_%s' % year_name,
-                'placeholder': _('Year') if self.is_required else False,
-            },
+            attrs={**context['widget']['attrs'], 'id': 'id_%s' % year_name},
         )
         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={
-                **context['widget']['attrs'],
-                'id': 'id_%s' % month_name,
-                'placeholder': _('Month') if self.is_required else False,
-            },
+            attrs={**context['widget']['attrs'], 'id': 'id_%s' % month_name},
         )
         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={
-                **context['widget']['attrs'],
-                'id': 'id_%s' % day_name,
-                'placeholder': _('Day') if self.is_required else False,
-            },
+            attrs={**context['widget']['attrs'], 'id': 'id_%s' % day_name},
         )
         subwidgets = []
         for field in self._parse_date_fmt():
diff --git a/docs/releases/3.0.txt b/docs/releases/3.0.txt
index d3656d6883..616b708389 100644
--- a/docs/releases/3.0.txt
+++ b/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.
diff --git a/tests/forms_tests/widget_tests/test_selectdatewidget.py b/tests/forms_tests/widget_tests/test_selectdatewidget.py
index 29f2f2399d..ea1c31b487 100644
--- a/tests/forms_tests/widget_tests/test_selectdatewidget.py
+++ b/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')