Here's what I see with the current patch in https://gerrit.wikimedia.org/r/#/c/197397/:

Seaching for "programming is ref*" highlights the phrase programming is referential in Functional programming is referential transparency.

Oh, actually, that looks like its working.... Are you using the experimental highlighter?

On enwiki, this does indeed appear to be problematic:

Ok - so this is an error in the highlighter I think. It must not know what to do with these queries. Its actually a reasonably fix - we reproduce it with the unit tests in https://github.com/wikimedia/search-highlighter and then fix it and backport the fix to the 1.3 branch there because we're still running Elasticsearch 1.3.

Now I'm having trouble reproducing this locally with the patch in https://gerrit.wikimedia.org/r/#/c/197397/:

This problem appears to be twofold:

1. The search highlighter seems to only work when we run our phrase_prefix query against text.plain -- not for title.plain, all.plain, etc.
2. With the new support for phrase_prefix queries, we can sometimes lose part of the query when highlight_query is set in other places in Searcher.php

This gets us halfway there: https://gerrit.wikimedia.org/r/#/c/201350/

Still to figure out - why phrase prefix highlighting is working for the title, but not the text.

Better: https://gerrit.wikimedia.org/r/#/c/201350/