Use of Gitlab api for issue and merge request templates retrieval.

[leifwar]

The current implementation of forge--topic-template for forge-gitlab-repository use local files under .gitlab (issues_templates & merge_requests_templates) folder on the main branch. Gitlab provides an api to extract this information directly from the server, where the main benefit for the Gitlab users would be support for group-level file templates.

I've tested the following implementation and it seems to work (I can create a pull if this is of interest?):

(cl-defmethod forge--topic-template ((repo forge-gitlab-repository)
                                     (class (subclass forge-topic)))
  (let* ((id (oref repo forge-id))
         (request_type (if (eq class 'forge-pullreq) "merge_requests" "issues"))
         (available-templates
          (--map (cdr (car it))
                 (forge--glab-get repo
                   (format "/projects/%s/templates/%s" id request_type))))
         (selected-template
           (if (cdr available-templates)
               (magit-completing-read
                (if (eq class 'forge-pullreq)
                    "Select pull-request template"
                  "Select issue template")
                available-templates
                nil t)
             (car available-templates))))
    (if selected-template
        (list
         (cons 'text (cdr (assoc 'content
                                 (forge--glab-get repo
                                   (format
                                     "/projects/%s/templates/%s/%s" id
                                     request_type selected-template))
                                 )))))))

I see that github also have organization level templates though I've not been able to find an api to retrieve these.