PortalTransforms: update transforms/rest for zope4 compatibility

Update to https://github.com/plone/Products.PortalTransforms/blob/3.2.0/Products/PortalTransforms/transforms/rest.py
because Zope4 no longer ship with a reStructuredText module and recommend
using docutils directly instead, which is what upstream did.

( in zope4py2 branch this was working because slapos patch
component/egg-patch/Zope/0001-OFS-XMLExportImport.patch used to bring
back reStructuredText but we don't seem to need it )

product/PortalTransforms/transforms/rest.py

+# -*- coding: utf-8 -*-
 from Products.PortalTransforms.interfaces import ITransform
+from docutils.core import publish_parts
 from zope.interface import implementer
-from reStructuredText import HTML
-import sys
+
+import six
+
 
 @implementer(ITransform)
-class rest:
+class rest(object):
     r"""Converts from reST to HTML.
 
       >>> transform = rest()
@@ -13,7 +16,7 @@ class rest:
       ...         self.value = data
 
       >>> data = transform.convert('*hello world*', D())
-      >>> print data.value
+      >>> print(data.value)
       <p><em>hello world</em></p>
       <BLANKLINE>
 
@@ -21,25 +24,25 @@ class rest:
     default:
 
       >>> try:
-      ...     out = transform.convert('.. raw:: html\n  :file: <isonum.txt>', D())
+      ...     out = transform.convert('.. raw:: html\n  :file: <isonum.txt>', D())  # noqa
       ... except NotImplementedError:
-      ...     print 'Good'
+      ...     print('Good')
       ... else:
       ...     if "&quot;raw&quot; directive disabled." in out.value:
-      ...         print 'Good'
+      ...         print('Good')
       ...     else:
-      ...         print 'Failure'
+      ...         print('Failure')
       Good
 
       >>> try:
       ...     out = transform.convert('.. include:: <isonum.txt>', D())
       ... except NotImplementedError:
-      ...     print 'Good'
+      ...     print('Good')
       ... else:
       ...     if "&quot;include&quot; directive disabled." in out.value:
-      ...         print 'Good'
+      ...         print('Good')
       ...     else:
-      ...         print 'Failure'
+      ...         print('Failure')
       Good
     """
 
@@ -47,29 +50,105 @@ class rest:
     inputs = ("text/x-rst", "text/restructured",)
     output = "text/html"
 
+    def __init__(self, name=None, **kwargs):
+        if name:
+            self.__name__ = name
+
+        self.config = {
+            'inputs': self.inputs,
+            'output': self.output,
+            'report_level': 2,
+            'initial_header_level': 2,
+        }
+
+        self.config_metadata = {
+            'inputs':
+                ('list', 'Inputs', 'Input(s) MIME type. Change with care.'),
+            'initial_header_level':
+                ('int', 'Initial Header Level',
+                 'Level of first header tag. Setting it to "2" will make '
+                 'the first header be "<h2>".'),
+            'report_level':
+                ('int', 'Report Level',
+                 'Level of error reporting. Set to "1" will display all '
+                 'messages. Setting it to "5" will display no messages.'),
+        }
+
+        self.config.update(kwargs)
+
     def name(self):
         return self.__name__
 
     def convert(self, orig, data, **kwargs):
         # do the format
+        writer_name = kwargs.get('writer_name', 'html4css1')
+
         encoding = kwargs.get('encoding', 'utf-8')
         input_encoding = kwargs.get('input_encoding', encoding)
         output_encoding = kwargs.get('output_encoding', encoding)
         language = kwargs.get('language', 'en')
-        warnings        = kwargs.get('warnings', None)
-        settings = {'documentclass': '',
+        initial_header_level = int(self.config.get('initial_header_level', 2))
+        report_level = int(self.config.get('report_level', 2))
+        # Note: we must NOT use warning_stream and stylesheet, because an attacker can abuse them.
+        # See https://sourceforge.net/p/docutils/bugs/413/
+        # Part of PloneHotfix20210518.
+        # It would be okay if we can be sure this method is called from trusted Python code,
+        # but we cannot be sure.
+        # We keep them in the settings, to be sure nothing changes due to this fix.
+        settings = {
+            'documentclass': '',
             'traceback': 1,
+            'input_encoding': input_encoding,
+            'output_encoding': output_encoding,
+            'stylesheet': None,
+            'stylesheet_path': None,
+            'file_insertion_enabled': 0,
+            'raw_enabled': 0,
+            'language_code': language,
+            # starting level for <H> elements:
+            'initial_header_level': initial_header_level + 1,
+            # set the reporting level to something sane:
+            'report_level': report_level,
+            # don't break if we get errors:
+            'halt_level': 6,
+            # remember warnings:
+            'warning_stream': None
         }
-        html = HTML(orig,
-                    report_level=2,
-                    input_encoding=input_encoding,
-                    output_encoding=output_encoding,
-                    language_code=language,
-                    warnings=warnings,
-                    settings=settings)
+
+        parts = publish_parts(
+            source=orig,
+            writer_name=writer_name,
+            settings_overrides=settings,
+            config_section='zope application'
+        )
+
+        header = '<h%(level)s class="title">%(title)s</h%(level)s>\n' % {
+            'level': initial_header_level,
+            'title': parts['title']}
+
+        subheader = '<h%(level)s class="subtitle">%(subtitle)s</h%(level)s>\n' % {  # noqa
+            'level': initial_header_level+1,
+            'subtitle': parts['subtitle']}
+
+        body = '%(docinfo)s%(body)s' % {
+            'docinfo': parts['docinfo'],
+            'body': parts['body']}
+
+        html = ''
+        if parts['title']:
+            html = html + header
+        if parts['subtitle']:
+            html = html + subheader
+        html = html + body
+
+        # TODO: check if this unicode condition works on Python 3.
+        if six.PY2 and output_encoding != 'unicode':
+            html = html.encode(output_encoding)
+
         html = html.replace(' class="document"', '', 1)
         data.setData(html)
         return data
 
+
 def register():
     return rest()