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>

1 files changed, 55 insertions, 40 deletions

diff --git a/django/forms/forms.py b/django/forms/forms.py
index 2bf268ae76..589b4693fd 100644
--- a/django/forms/forms.py
+++ b/django/forms/forms.py
@@ -4,15 +4,17 @@ Form classes
 
 import copy
 import datetime
+import warnings
 
 from django.core.exceptions import NON_FIELD_ERRORS, ValidationError
 from django.forms.fields import Field, FileField
-from django.forms.utils import ErrorDict, ErrorList
+from django.forms.utils import ErrorDict, ErrorList, RenderableFormMixin
 from django.forms.widgets import Media, MediaDefiningClass
 from django.utils.datastructures import MultiValueDict
+from django.utils.deprecation import RemovedInDjango50Warning
 from django.utils.functional import cached_property
-from django.utils.html import conditional_escape, html_safe
-from django.utils.safestring import mark_safe
+from django.utils.html import conditional_escape
+from django.utils.safestring import SafeString, mark_safe
 from django.utils.translation import gettext as _
 
 from .renderers import get_default_renderer
@@ -49,8 +51,7 @@ class DeclarativeFieldsMetaclass(MediaDefiningClass):
         return new_class
 
 
-@html_safe
-class BaseForm:
+class BaseForm(RenderableFormMixin):
     """
     The main implementation of all the Form logic. Note that this class is
     different than Form. See the comments by the Form class for more info. Any
@@ -62,6 +63,12 @@ class BaseForm:
     prefix = None
     use_required_attribute = True
 
+    template_name = 'django/forms/default.html'
+    template_name_p = 'django/forms/p.html'
+    template_name_table = 'django/forms/table.html'
+    template_name_ul = 'django/forms/ul.html'
+    template_name_label = 'django/forms/label.html'
+
     def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
                  initial=None, error_class=ErrorList, label_suffix=None,
                  empty_permitted=False, field_order=None, use_required_attribute=None, renderer=None):
@@ -129,9 +136,6 @@ class BaseForm:
         fields.update(self.fields)  # add remaining fields in original order
         self.fields = fields
 
-    def __str__(self):
-        return self.as_table()
-
     def __repr__(self):
         if self._errors is None:
             is_valid = "Unknown"
@@ -206,6 +210,12 @@ class BaseForm:
 
     def _html_output(self, normal_row, error_row, row_ender, help_text_html, errors_on_separate_row):
         "Output HTML. Used by as_table(), as_ul(), as_p()."
+        warnings.warn(
+            'django.forms.BaseForm._html_output() is deprecated. '
+            'Please use .render() and .get_context() instead.',
+            RemovedInDjango50Warning,
+            stacklevel=2,
+        )
         # Errors that should be displayed above all fields.
         top_errors = self.non_field_errors().copy()
         output, hidden_fields = [], []
@@ -282,35 +292,37 @@ class BaseForm:
                 output.append(str_hidden)
         return mark_safe('\n'.join(output))
 
-    def as_table(self):
-        "Return this form rendered as HTML <tr>s -- excluding the <table></table>."
-        return self._html_output(
-            normal_row='<tr%(html_class_attr)s><th>%(label)s</th><td>%(errors)s%(field)s%(help_text)s</td></tr>',
-            error_row='<tr><td colspan="2">%s</td></tr>',
-            row_ender='</td></tr>',
-            help_text_html='<br><span class="helptext">%s</span>',
-            errors_on_separate_row=False,
-        )
-
-    def as_ul(self):
-        "Return this form rendered as HTML <li>s -- excluding the <ul></ul>."
-        return self._html_output(
-            normal_row='<li%(html_class_attr)s>%(errors)s%(label)s %(field)s%(help_text)s</li>',
-            error_row='<li>%s</li>',
-            row_ender='</li>',
-            help_text_html=' <span class="helptext">%s</span>',
-            errors_on_separate_row=False,
-        )
-
-    def as_p(self):
-        "Return this form rendered as HTML <p>s."
-        return self._html_output(
-            normal_row='<p%(html_class_attr)s>%(label)s %(field)s%(help_text)s</p>',
-            error_row='%s',
-            row_ender='</p>',
-            help_text_html=' <span class="helptext">%s</span>',
-            errors_on_separate_row=True,
-        )
+    def get_context(self):
+        fields = []
+        hidden_fields = []
+        top_errors = self.non_field_errors().copy()
+        for name, bf in self._bound_items():
+            bf_errors = self.error_class(bf.errors, renderer=self.renderer)
+            if bf.is_hidden:
+                if bf_errors:
+                    top_errors += [
+                        _('(Hidden field %(name)s) %(error)s') % {'name': name, 'error': str(e)}
+                        for e in bf_errors
+                    ]
+                hidden_fields.append(bf)
+            else:
+                errors_str = str(bf_errors)
+                # RemovedInDjango50Warning.
+                if not isinstance(errors_str, SafeString):
+                    warnings.warn(
+                        f'Returning a plain string from '
+                        f'{self.error_class.__name__} is deprecated. Please '
+                        f'customize via the template system instead.',
+                        RemovedInDjango50Warning,
+                    )
+                    errors_str = mark_safe(errors_str)
+                fields.append((bf, errors_str))
+        return {
+            'form': self,
+            'fields': fields,
+            'hidden_fields': hidden_fields,
+            'errors': top_errors,
+        }
 
     def non_field_errors(self):
         """
@@ -318,7 +330,10 @@ class BaseForm:
         field -- i.e., from Form.clean(). Return an empty ErrorList if there
         are none.
         """
-        return self.errors.get(NON_FIELD_ERRORS, self.error_class(error_class='nonfield'))
+        return self.errors.get(
+            NON_FIELD_ERRORS,
+            self.error_class(error_class='nonfield', renderer=self.renderer),
+        )
 
     def add_error(self, field, error):
         """
@@ -360,9 +375,9 @@ class BaseForm:
                     raise ValueError(
                         "'%s' has no field named '%s'." % (self.__class__.__name__, field))
                 if field == NON_FIELD_ERRORS:
-                    self._errors[field] = self.error_class(error_class='nonfield')
+                    self._errors[field] = self.error_class(error_class='nonfield', renderer=self.renderer)
                 else:
-                    self._errors[field] = self.error_class()
+                    self._errors[field] = self.error_class(renderer=self.renderer)
             self._errors[field].extend(error_list)
             if field in self.cleaned_data:
                 del self.cleaned_data[field]