Made m2m fields form help_text munging specific to admin widgets.

Refs #9321 and follow-up to e80de93af6.

django/contrib/admin/options.py

@@ -30,6 +30,7 @@ from django.db.models.sql.constants import QUERY_TERMS
 from django.forms.formsets import all_valid, DELETION_FIELD_NAME
 from django.forms.models import (modelform_factory, modelformset_factory,
     inlineformset_factory, BaseInlineFormSet, modelform_defines_fields)
+from django.forms.widgets import SelectMultiple, CheckboxSelectMultiple
 from django.http import Http404, HttpResponseRedirect
 from django.http.response import HttpResponseBase
 from django.shortcuts import get_object_or_404
@@ -41,6 +42,7 @@ from django.utils.encoding import force_text, python_2_unicode_compatible
 from django.utils.html import escape, escapejs
 from django.utils.http import urlencode
 from django.utils.text import capfirst, get_text_list
+from django.utils.translation import string_concat
 from django.utils.translation import ugettext as _
 from django.utils.translation import ungettext
 from django.utils.safestring import mark_safe
@@ -280,7 +282,12 @@ class BaseModelAdmin(six.with_metaclass(forms.MediaDefiningClass)):
             if queryset is not None:
                 kwargs['queryset'] = queryset
 
-        return db_field.formfield(**kwargs)
+        form_field = db_field.formfield(**kwargs)
+        if isinstance(form_field.widget, SelectMultiple) and not isinstance(form_field.widget, CheckboxSelectMultiple):
+            msg = _('Hold down "Control", or "Command" on a Mac, to select more than one.')
+            help_text = form_field.help_text
+            form_field.help_text = string_concat(help_text, ' ', msg) if help_text else msg
+        return form_field
 
     def get_view_on_site_url(self, obj=None):
         if obj is None or not self.view_on_site:

tests/admin_widgets/tests.py

@@ -19,6 +19,7 @@ from django.core.files.uploadedfile import SimpleUploadedFile
 from django.db.models import CharField, DateField
 from django.test import TestCase as DjangoTestCase
 from django.test import override_settings
+from django.utils import six
 from django.utils import translation
 
 from . import models
@@ -168,6 +169,17 @@ class AdminFormfieldForDBFieldTests(TestCase):
     def testInheritance(self):
         self.assertFormfield(models.Album, 'backside_art', widgets.AdminFileWidget)
 
+    def test_m2m_widgets(self):
+        """m2m fields help text as it applies to admin app (#9321)."""
+        class AdvisorAdmin(admin.ModelAdmin):
+            filter_vertical = ['companies']
+
+        self.assertFormfield(models.Advisor, 'companies', widgets.FilteredSelectMultiple,
+                             filter_vertical=['companies'])
+        ma = AdvisorAdmin(models.Advisor, admin.site)
+        f = ma.formfield_for_dbfield(models.Advisor._meta.get_field('companies'), request=None)
+        self.assertEqual(six.text_type(f.help_text), 'Hold down "Control", or "Command" on a Mac, to select more than one.')
+
 
 @override_settings(PASSWORD_HASHERS=('django.contrib.auth.hashers.SHA1PasswordHasher',))
 class AdminFormfieldForDBFieldWithRequestTests(DjangoTestCase):