Problem: Requested edits to protected pages, especially templates, may be untested, leading to rejection or delays as problems are resolved.
Who would benefit: Readers, as templates are fixed more accurately and promptly; editors requesting edits to protected templates; editors fulfilling such requests.
Proposed solution: Allow an editor to preview an edit to a protected template even if they would not be permitted to commit the edit.
More comments: "Preview page with this template" is extremely useful but has no effect when testing in a sandbox. Of course, the editor should see a prominent warning before working on the page that it would not be possible to save the change. Once an editor is happy with their work, I would expect them to copy and paste the edited source into a sandbox ready for promotion by a template editor. The feature could apply to all pages or just to templates and perhaps modules. If there are concerns that editors will waste time writing material that cannot be saved, then it could be an opt-in preference (off by default).
Could anger users as unsaveable: The idea of such editing, as an unsaveable protected page, is a topic for en:computer psychology, and most likely the better solution would be copy-to-sandbox, as noted above. The general strategy would be to avoid giving users "enough rope to hang themselves" just as dangling several nooses in a room could increase the risk of accidental hangings. Even as an opt-in mode, some users might imagine the page as saveable, before they realized the warnings. It would be very dangerous to allow preview editing unless the sandbox-save was understood as the only result, because enticing a user to spend hours editing the protected page, as if somehow useable, would likely trigger severe infuriating anger or livid outrage, because users often ignore short warnings of how the editing of a protected page could become a huge waste of time. The inability to edit a protected page really gets the user's attention, as no chance to save changes, rather than foster a false hope that careful, excellent changes surely would be saved. As for enable a run-preview of user-sandbox templates, that is a separate topic. -Wikid77 (talk) 10:19, 10 November 2018 (UTC)[reply]
Yes, we need to avoid that problem. This screen shouldn't be accessible via the normal Edit tab. Perhaps the header which appears on View Source could have an "Edit without saving for preview only" button. This item is a proposal rather then a completed design. At the time of writing I wasn't aware of Special:TemplateSandbox, which does the job in a roundabout and awkward way. Improving that special page to allow a /sandbox suffix rather than a prefix, and giving it more publicity (a mention on the View Source header?) might be a better solution, as the user could save the sandbox in the right place ready for promotion by a template editor or admin. Certes (talk) 10:33, 17 November 2018 (UTC)[reply]
The problem with Special:TemplateSandbox using a "/sandbox" suffix is that you'd wind up picking up the sandboxes of every template with a sandbox, not just the one you're trying to check, and many of those are likely to be outdated or broken. If you want to test with an existing /sandbox-suffixed page, you can create a redirect to it under an appropriate prefix. Anomie (talk) 14:18, 17 November 2018 (UTC)[reply]
I think such feature should generate some sort of diff file or url that can allow the user to share that directly to people with right to make such edit. C933103 (talk) 20:26, 20 November 2018 (UTC)[reply]
Support Probably the “View source” page could be preserved with a link/button somewhere on it (no separate tab) to emphasize the fact that the page cannot be edited. Tacsipacsi (talk) 15:48, 30 November 2018 (UTC)[reply]
Support James Martindale (talk) 19:36, 16 November 2018 (UTC)