Fix panic when slicing RTL text with non-monotonic clusters#1078
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Fix panic when slicing RTL text with non-monotonic clusters#1078StefanoD wants to merge 1 commit into
StefanoD wants to merge 1 commit into
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`shape_text_with_font` assumed the shaper returns glyph clusters of an
RTL run in strictly descending order, computing a cluster's byte range as
`cluster[i]..cluster[i-1]`. Some fonts/shapers violate this (e.g. some
builds of Times New Roman shaping the Arabic text "الويب" return ascending
clusters `[0, 2, 4, 6, 8]` for the RTL run), which made `start > end` and
panicked when slicing the source text ("byte range starts at 2 but ends
at 0").
Extract the boundary computation into `glyph_cluster_byte_range` and
normalize the range so `start <= end` always holds. Both ends stay on
cluster (char) boundaries, so the slice remains UTF-8 safe.
Add unit tests covering the LTR, normal RTL, and the non-monotonic RTL
case from the bug report.
Fixes linebender#1044
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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shape_text_with_fontassumed the shaper returns glyph clusters of an RTL run in strictly descending order, computing a cluster's byte range ascluster[i]..cluster[i-1]. Some fonts/shapers violate this (e.g. some builds of Times New Roman shaping the Arabic text "الويب" return ascending clusters[0, 2, 4, 6, 8]for the RTL run), which madestart > endand panicked when slicing the source text ("byte range starts at 2 but ends at 0").Extract the boundary computation into
glyph_cluster_byte_rangeand normalize the range sostart <= endalways holds. Both ends stay on cluster (char) boundaries, so the slice remains UTF-8 safe.Add unit tests covering the LTR, normal RTL, and the non-monotonic RTL case from the bug report.
Fixes #1044
Generated by Claude
Note: I accidentally closed the original PR (#1060) by deleting my fork, which auto-closed it. This reopens the same change — the branch and commits are unchanged.