We discovered that harfbuzz 1.8.8 breaks WebKit by changing the ownership semantics of hb_icu_get_unicode_funcs() from (transfer full) to (transfer none). Our code was actually expecting (transfer none), so it's not immediately clear to me why it's crashing now, but doesn't matter as per Behdad:
"Please just remove that line of code. hb-buffer comes up prepared with unicode-funcs these days (has had, for at least five years). Just removing that line completely results in better output."
This should be covered by all our complex text tests if the bots were upgraded to the newer harfbuzz.
Created attachment 351905 [details]
Comment on attachment 351905 [details]
Clearing flags on attachment: 351905
Committed r236985: <https://trac.webkit.org/changeset/236985>
All reviewed patches have been landed. Closing bug.