[REF] mail: improve composer call to template values generation

Now that template generation methods have been cleaned we can cleanup calls
done in composer. We notably

  * make methods private, improve their naming and docstrings;
  * better support input / output of asked fields;
  * be more coherent with composer fields and template fields usage;

Task-2710804 (Mail: Clean MailThread Posting API)
Prepares Task-2088884 (Mail: Composer Onchange to Editable Computed Stored)

Part-of: odoo/odoo#99482

addons/mail/wizard/mail_compose_message.py

@@ -203,12 +203,11 @@ class MailComposer(models.TransientModel):
             -> for x2many field, this onchange return command instead of ids
         """
         if template_id and composition_mode == 'mass_mail':
+            # copy raw template values (not rendered due to mass mode)
             template = self.env['mail.template'].browse(template_id)
             values = dict(
                 (field, template[field])
-                for field in ('body_html',
-                              'email_from',
-                              'mail_server_id',
+                for field in ('email_from',
                               'reply_to',
                               'subject',
                              )
@@ -218,16 +217,20 @@ class MailComposer(models.TransientModel):
                 values['attachment_ids'] = [att.id for att in template.attachment_ids]
             if template.mail_server_id:
                 values['mail_server_id'] = template.mail_server_id.id
+            if not tools.is_html_empty(template.body_html):
+                values['body'] = template.body_html
         elif template_id:
-            values = self._generate_email_for_composer(
-                template_id, [res_id],
+            # render template (mono record, comment mode) and set it as composer values
+            values = self._generate_template_for_composer(
+                self.env['mail.template'].browse(template_id),
+                [res_id],
                 ('attachment_ids',
                  'body_html',
                  'email_cc',
                  'email_from',
                  'email_to',
                  'mail_server_id',
-                 'partner_to',
+                 'partner_ids',
                  'reply_to',
                  'report_template',
                  'subject',
@@ -276,9 +279,6 @@ class MailComposer(models.TransientModel):
                             'subject',
                            ) if key in default_values)
 
-        if values.get('body_html'):
-            values['body'] = values.pop('body_html')
-
         # This onchange should return command instead of ids for x2many field.
         values = self._convert_to_write(values)
 
@@ -642,13 +642,14 @@ class MailComposer(models.TransientModel):
 
         # generate template-based values
         if self.template_id:
-            template_values = self._generate_email_for_composer(
-                self.template_id.id, res_ids,
+            template_values = self._generate_template_for_composer(
+                self.template_id,
+                res_ids,
                 ('attachment_ids',
                  'email_to',
                  'email_cc',
                  'mail_server_id',
-                 'partner_to',
+                 'partner_ids',
                  'report_template',
                 )
             )
@@ -670,26 +671,55 @@ class MailComposer(models.TransientModel):
 
         return template_values
 
-    @api.model
-    def _generate_email_for_composer(self, template_id, res_ids, render_fields):
-        """ Call email_template._generate_template(), get fields relevant for
-            mail.compose.message, transform email_cc and email_to into partner_ids """
-        returned_fields = list(render_fields) + ['partner_ids']
-        if 'report_template' in render_fields:
-            returned_fields.append('attachments')
-        values = dict.fromkeys(res_ids, False)
+    def _generate_template_for_composer(self, template, res_ids, render_fields,
+                                        find_or_create_partners=True):
+        """ Generate values based on template and relevant values for the
+        mail.compose.message wizard.
 
-        template_values = self.env['mail.template'].browse(template_id)._generate_template(
+        :param record template: a mail template, as during onchange mode it
+          may not be set on self (to remove when removing the onchange);
+        :param list res_ids: list of record IDs on which template is rendered;
+        :param list render_fields: list of fields to render on template;
+        :param boolean find_or_create_partners: transform emails into partners
+          (see ``Template._generate_template_recipients``);
+
+        :returns: a dict containing all asked fields for each record ID given by
+          res_ids. Note that
+
+          * 'body' comes from template 'body_html' generation;
+          * 'attachments' is an additional key coming with 'attachment_ids' due
+            to report generation (in the format [(report_name, data)] where data
+            is base64 encoded);
+          * 'partner_ids' is returned due to recipients generation that gives
+            partner ids coming from default computation as well as from email
+            to partner convert (see ``find_or_create_partners``);
+        """
+        self.ensure_one()
+
+        # some fields behave / are named differently on template model
+        mapping = {
+            'attachments': 'report_template',
+            'body': 'body_html',
+            'partner_ids': 'partner_to',
+        }
+        template_fields = {mapping.get(fname, fname) for fname in render_fields}
+        template_values = template._generate_template(
             res_ids,
-            render_fields,
+            template_fields,
             find_or_create_partners=True
         )
-        for res_id in res_ids:
-            res_id_values = dict((field, template_values[res_id][field]) for field in returned_fields if template_values[res_id].get(field))
-            res_id_values['body'] = res_id_values.pop('body_html', '')
-            values[res_id] = res_id_values
 
-        return values
+        exclusion_list = ('email_cc', 'email_to') if find_or_create_partners else ()
+        mapping = {'body_html': 'body'}
+        render_results = {}
+        for res_id in res_ids:
+            render_results[res_id] = {
+                mapping.get(fname, fname): value
+                for fname, value in template_values[res_id].items()
+                if fname not in exclusion_list and value
+            }
+
+        return render_results
 
     # ----------------------------------------------------------------------
     # EMAIL MANAGEMENT

addons/test_mail/tests/test_mail_composer.py

@@ -593,14 +593,13 @@ class TestComposerInternals(TestMailComposer):
                 self.assertEqual(composer.subject, 'Back to my amazing subject for {{ record.name }}')
 
                 # update with template with void values: void value is not forced in
-                # rendering mode as well as when copying template values, except for
-                # body in rendering mode
+                # rendering mode as well as when copying template values
                 composer.write({'template_id': template_void.id})
                 # currently onchange necessary
                 composer._onchange_template_id_wrapper()
 
                 if composition_mode == 'comment':
-                    self.assertFalse(composer.body, 'Void template body resets while other fields not, maybe to fix')
+                    self.assertEqual(composer.body, 'Back to my amazing body')
                     self.assertEqual(composer.mail_server_id, self.mail_server_global)
                     self.assertEqual(composer.record_name, 'Manual update')
                     self.assertEqual(composer.subject, 'Back to my amazing subject for {{ record.name }}')