No RST syntaxt highlighting in the ACE editor

Summary

It seems that ReStructuredText syntax is not highlighted while editing (contrastively, e.g. Markdown is).

Steps to reproduce

Open any RST file, click "Edit", do not see syntax highlighting.

Example Project

https://gitlab.com/mgielda/no-rst-highlighting/blob/master/example.rst - try to edit the file.

What is the current bug behavior?

No syntax highlighting.

What is the expected correct behavior?

Normal syntax highlighting, like for markdown on GitLab, like for RST on the ACE example site.

Relevant logs and/or screenshots

As visible on the screenshot, this works in ACE.

This bug happens on GitLab.com

Possible fixes

Not strictly code, but if you inspect the HTML of the editor, you see:

<form class="form-horizontal js-quick-submit js-requires-input js-edit-blob-form" data-relative-url-root="null" data-assets-prefix="/assets" data-blob-language="text" action="/mgielda/no-rst-highlighting/update/master/example.rst" accept-charset="UTF-8" method="post"><input name="utf8" type="hidden" value="✓">

Now for markdown the data-blob-language is 'markdown'. Clearly, here it should be 'rst' or something similar, and probably the underlying code is wrong. But looks like an easy problem to fix.