Guard GPOS mark attachment against attach_chain overflow - #480
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A mark more than i16::MAX glyphs after its base stored a truncated attach_chain and was positioned relative to the wrong glyph. HarfBuzz checks for this and leaves the mark unattached (MarkArray.hh). Do the same, as harfbuzz#411 does for cursive attachment.
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Mark attachment stores the distance to the base in
attach_chainwith(glyph_pos as isize - idx as isize) as i16(harfrust/src/hb/ot/gpos/mark.rs:85), which truncates when a mark is more thani16::MAXglyphs after its base. HarfBuzz checks this inMarkArray::apply(MarkArray.hh, from harfbuzz#5636) and leaves the mark unattached; #411 ported the cursive half of that change.xfollowed by 33000 U+0301 with--features=-mkmkandtests/fonts/rb_custom/BungeeTint-Regular.ttf: HarfBuzz 14.5 attaches the first 32768 marks at@-369,0and leaves the remaining 232 at@0,0; main places those 232 at@368,0(the chain wraps to a later glyph).This checks the distance with
i16::try_frombefore writing the offsets and, on overflow, setsattach_chainto 0 and moves on, as HarfBuzz does. Marks within range are unchanged.mark_too_far_from_its_base_is_left_unattachedsits next to the issue 384 tests intests/shaping/regressions.rs; it fails on main.cargo fmt --check,cargo clippy -p harfrust --all-features --all-targets -D warningsandcargo test -p harfrustpass; I did not run the MSRV, no-default-features, icu or thumbv7em jobs. CHANGELOG entry added under Unreleased, as in #411.Written with AI assistance (Claude); I have reviewed the change.