Created attachment 471660 [details] demonstration of combining mark not being drawn Safari is not drawing the Combining Long Solidus Overlay character in this font in some situations, such as in the attached demo. It is drawn in other browsers.
Disabling IFC feature fixes this.
This is caused by a paint optimization we have in IFC. The character is measured to be 0px wide (glyph has 0 advance width) and since it's the only content of the out-of-flow box, the box itself ends up being 0px wide too (see shrink-to-fit sizing) and we (erroneously) decide to not paint it -even though there's glyph overflow. (among other things, decoration (e.g. border) throws us off of this "fast" codepath)
<rdar://problem/129732893>
Created attachment 471682 [details] Patch
Created attachment 471685 [details] Patch
Committed 280057@main (8789afc340e4): <https://commits.webkit.org/280057@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 471685 [details].