In r44919 I've gone ahead and reimplemented bug 2585, so a page view for
a nonexistent page will return a "404 Not Found" HTTP status code
instead of a "200 OK".
This will allow bots and spiders to detect broken links from the outside
web to bad or deleted wiki pages, but should be totally transparent to
end-users.
When we first attempted this in 2005, the 404 was also applied to
action=edit pages... We had a large number of reports from active
editors that they were having trouble creating articles, with the edit
page not loading properly.
Since this was disrupting basic site activity, we ended up reverting it
before we had a chance to really track it down -- none of the developers
could reproduce it at the time.
The size of our base HTML from even the simplest skin should be enough
to avoid tripping Internet Explorer's "friendly error pages", and we
were unable to track down any specific browser, ISP proxy, or other
hypothetical problem source.
If people do encounter problems once this goes live, it at least
shouldn't affect primary wiki functionality while we reproduce and fix
it -- hitting a raw page view for a nonexistent page is something that
you usually have to jump through some hoops to do within the wiki.
After things have settled a bit, we'll probably start using more 4xx and
5xx status codes for various error pages.
-- brion