fluff: Add [restore this revision] link to old revisions

[Amorymeltzer]

1st commit: Tidies up and removes duplicate/unnecessary code

• The same four lines, three of which used spanTag, were repeated frequently
• Newer revisions either are the latest or not
• No idea what .firstrevisionheader did but I can't find it anywhere on-wiki, so removed

2nd commit: Add [restore this revision] link to oldid pages

fluff: Add [restore this revision] link to oldid pages, closes #131

Checking for wgDiffOldId and wgDiffNewId excludes Special:Undelete, and so should be sufficient to avoid problematic diffs. Some of the logic/checks may be a tad confusing since wgDiffNewId and wgDiffOldId have different behaviors (see [[phab:T214985]]). One advantage of the restructuring is that [restore this revision] will now appear when viewing the first revision as a diff with diff=prev, as may sometimes happen.

One thing to note is that when viewing old revisions, checking for div#mw-revision-info sufficiently prevents the link from appearing on the most recent revision, since div#mw-revision-info-current is used instead. However, that is only the case if there is anything present at [[MediaWiki:Revision-info-current]], elsewise the fallback is to use div#mw-revision-info; this may have issues for other wikis if that page doesn't exist. Moreover, unlike revisionasof, $3 in revision-info doesn't expose a link we can capture, hence the imperfect Morebits.query('oldid') appears the best we can do.

[MusikAnimal]

At cursory glance this seems to work well. I am a little concerned about checking the DOM for .mw-revision-info. What about comparing wgRevisionId and wgCurRevisionId? Could that work?

Visually, my only concern is proximity of the [restore this version] link to the breadcrumbs (say if you're viewing a subpage). I don't have any good ideas on how to address this... but I do see misclicks happening. Minor issue.

The link is pretty tiny too, but I suppose that's just a consequence of how that part of the page is styled by MediaWiki (or Common.css, etc).

[Amorymeltzer]

@MusikAnimal:

What about comparing wgRevisionId and wgCurRevisionId

That was my initial plan, but ran into a few issues. The more minor one is that on deleted pages, the two are the same (0), and I was trying to simplify things by removing that. The larger issue is that wgRevisionId and wgCurRevisionId don't help distinguish diffs from old revisions, but #mw-revision-info does. It's avoidable if you test (and fail to find) #mw-diff-otitle1 and #mw-diff-otitle1, but that's just relying on a different id, so isn't much help. Using #mw-revision-info simplifies the logic quite a bit.

Visually, my only concern is proximity of the [restore this version] link to the breadcrumbs (say if you're viewing a subpage).

Ditto. I first tried putting it above the diff nav links, but I think that's even more likely to cause misclicks. I think the real issue is that, unlike diffs, this stuff isn't centered, so it all seems off-kilter and tiny next to the comparatively-giant message from #mw-revision-info. Discoverability is definitely an issue, although I hope folks are familiar enough with the bold brown text to spot it.

[Amorymeltzer]

Ignored my own advice in 8550975, so this took a while to get back to. After going through all the conflicts, I ended up refactoring this too much, so I'm closing this in favor of #561 (cosmetics) and #562 (the meat).