How to reproduce:
get a fatal.
log error:
{"id":"WBMcZwpAIDIAAHvzlbUAAAAM","type":"RuntimeException","file":"/srv/mediawiki/php-1.28.0-wmf.23/extensions/CirrusSearch/includes/ElasticsearchIntermediary.php","line":113,"message":"No search request was made","code":0,"url":"/?search=%E3%80%80","backChange 318548 had a related patch set uploaded (by DCausse):
Fix errors when searching ideographic whitespaces and keep track of the original query
I looked at the patch and it looks like it will do the trick. While it would avoid the fatal error in the bug, should we also do something with other space characters? Several starting at U+2000 (%E2%80%8A) return the same 4 results on enwiki, 2 on frwiki, and 3 on dewiki—with the apostrophe article being common to all the results. Something interesting is going on there, but if it's out of scope for this ticket, that's fine.
I've merged the existing patch. I think the other space characters probably deserve a ticket of their own?
Change 318548 merged by jenkins-bot:
Fix errors when searching ideographic whitespaces and keep track of the original query
@TJones: the main purpose of excluding U+3000 is that it was generating a match_all query (according to the comment in the code). It is expensive and does not bring any particular benefits. I did not look deeply into other whitespaces but since they do return some results I'm fine keeping them (performance wise).
If you have other concerns I'm OK to explore possible solutions and dig into this.