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…h across stringWidth, sliceAnsi and console.table The width table generator now derives every field from the Unicode 17 Character Database instead of a hand-kept zero-width list and grapheme classes carried over from a Unicode 15.1 table. Format characters (Cf) and unassigned default-ignorable codepoints are zero-width, unassigned codepoints and Indic letters are narrow, Emoji_Presentation codepoints (the regional indicators) are wide, and the grapheme classes include the Unicode 16/17 InCB consonants and Extended_Pictographic changes. GraphemeState moves to stringWidth.h and is shared with sliceAnsi.cpp. A keycap needs a [0-9#*] base, a lone regional indicator is a wide emoji, an emoji modifier extends any base without widening it, the copyright and registered signs are emoji bases, and controls end a cluster on both sides. The UTF-8 width path (console.table column sizing, the markdown renderer) now clusters graphemes the same way as Bun.stringWidth.
WalkthroughThe generator now derives Unicode 17 classifications from UCD files. Shared grapheme state powers width measurement, ANSI slicing, and wrapping. Tests cover Unicode properties, grapheme clusters, zero-width marks, and ANSI behavior. ChangesUnicode grapheme-aware width
Merge Risk: 🔵 Low · up to Some Unicode sequences can be merged incorrectly and report the wrong display width across shared string-width consumers. The impact is bounded, but the classification should be corrected. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Updated 1:17 PM PT - Sep 6th, 2026
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…luster on the bulk paths wrapWord in wrapAnsi.cpp advanced one codepoint at a time with the per-codepoint width, so a flag (two wide regional indicators) was split across rows. It now gathers one cluster with the shared GraphemeState. The UTF-16 bulk kernels and the UTF-8 ASCII run seeded a new cluster with their first unit even when a pending Prepend joins it (GB9b). That unit now goes through the scalar path, so stringWidth, sliceAnsi and console.table agree on U+0600 followed by a keycap. The width-only UTF-8 walk counts ASCII runs with the SIMD kernel again. The wrapAnsi cluster-fusing table keeps its comments and escapes; only the expected column of the 44 changed rows differs from main.
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…ngwidth-property-tables
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The four points from the earlier review are addressed in e03f243 — wrapWord now gathers whole clusters via the shared GraphemeState, both the UTF-8 and UTF-16 bulk paths guard the first unit with joinsPendingCluster() before seeding, the width-only walkUTF8ExcludeANSI<false> counts ASCII runs with SIMD visibleLatin1Width again, and the regenerated wrapAnsi test rows keep \uXXXX escapes with their per-group intent comments restored. The one inline finding below is new to that fix commit.
Extended reasoning...
Re-checked each of the four earlier threads against e03f243: wrapWord no longer calls Bun__codepointWidth per codepoint (the RI-flag-split case is covered by a new test at wrapAnsi.test.ts:113); joinsPendingCluster() gates both walkUTF8ExcludeANSI line 621 and UTF16WidthAccumulator::addRun line 762 so a Prepend's successor goes through addCodepoint (covered by the new "Prepend joins the codepoint after it on every path" test); the kReportClusters=false specialization restores visibleLatin1Width({p, asciiLen-1}) for visibleUTF8WidthExcludeANSI; and the test table now uses ️ / ́ / \u{1F44D}\u{1F3FF} escapes with the group comments back. The new inline finding is a side-effect of changing the post-append vis == columns guard to vis >= columns in the same commit that made clusterWidth able to exceed columns.
A cluster wider than the row already starts a new row through the check before it is placed. The check after it must only fire on an exact fill, or two over-wide clusters in a row get a blank row between them.
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The wrapWord double-blank-row regression from the last round is fixed (853c840 reverts to vis == columns and adds the over-wide-cluster tests), and the earlier three findings were addressed in e03f243 — I have nothing further to raise. Given the scope (regenerated width tables, a rewritten cluster-width state machine shared across four user-facing entry points, and ~45 regenerated wrapAnsi expectations), a human pass on the UCD-derivation choices and the kept-convention deltas listed in the PR notes would still be worthwhile.
What was reviewed:
wrapWordcluster loop after the==revert — traced exact-fill, over-wide-cluster, and mixed-width sequences; the pre-check handles overflow and the post-check only fires on exact fill, matching base semantics.- The Prepend + bulk-path seeding fix in
walkUTF8ExcludeANSI/UTF16WidthAccumulator::addRun— the first unit after a Prepend now routes throughaddCodepoint, sokeycapBaseis set from the real cluster base. GraphemeBreakClass::Controladdition — the packed-byte layout,kGraphemeBreakClassCount, and the GB4/GB5 table rows are consistent.
Extended reasoning...
Overview
This PR reworks Bun.stringWidth's Unicode width tables to be derived entirely from UCD 17.0 property files instead of hand-maintained range lists, and unifies the grapheme-cluster width accumulator across Bun.stringWidth, Bun.sliceAnsi, Bun.wrapAnsi, and the UTF-8 width path used by console.table. The generator script (generate-stringwidth-tables.mjs) is rewritten, stringWidthTables.h is regenerated, GraphemeState and the packed-byte accessors move into stringWidth.h, sliceAnsi.cpp and wrapAnsi.cpp drop their duplicated width state and share the header implementation, and the UTF-8 walker becomes cluster-aware. Tests across three files gain new coverage for the UCD-derived classifications, Prepend clusters, and hard-wrap-by-cluster.
Over three prior review rounds I raised four issues (wrapWord still summing per-codepoint width for regional indicators, Prepend + bulk-path keycapBase divergence, loss of the SIMD ASCII fast path in the width-only UTF-8 walker, and regenerated test rows losing escape sequences and intent comments), then a fifth (vis >= columns producing blank rows between consecutive over-wide clusters). Commits e03f243 and 853c840 addressed all of them, each with regression tests. This run's hunt reached dry_streak with no new findings.
Security risks
None identified. The change operates on in-memory string data with bounded table lookups; the three-stage table indices are derived from codepoints clamped to the Unicode range, and no untrusted length or offset drives an allocation. There is no auth, crypto, filesystem, or network surface in the diff.
Level of scrutiny
High. This is ~1,280 lines of net change to a shared width algorithm that four user-facing APIs depend on, including a regenerated 1,100-line lookup table and a rewritten cluster state machine whose correctness hinges on UAX #29 rule ordering. The PR description documents 117 intentional deviations from the ICU/node reference and three "kept conventions" — those are policy choices a maintainer should sign off on rather than an automated reviewer. The regenerated wrapAnsi.test.ts expectation table (~45 rows) was produced by re-running the new build against the inputs, which is exactly the snapshot-certifies-the-bug risk REVIEW.md calls out; the author's per-row stringWidth(row) <= columns check mitigates it but a human spot-check of a few rows against a terminal would add confidence.
Other factors
Test coverage for the specific regressions raised in review is good: each of the five findings now has a dedicated assertion in wrapAnsi.test.ts or stringWidth.test.ts. The GraphemeBreakClass::Control addition was checked against the packed-byte bit budget and every consumer of kGraphemeBreakClassCount. The Bun__isEmojiPresentation export removal was verified to have no remaining callers. All third-party review threads on the timeline are github-actions lint bot comments (self-resolved after the comment-shortening commit) rather than substantive human objections; there is no outstanding CHANGES_REQUESTED review.
A single regional indicator stays narrow, as string-width reports it and as the existing tests pinned it. Only the pair (a flag) is wide, and a combining mark after a lone one no longer changes that.
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In `@scripts/generate-stringwidth-tables.mjs`:
- Line 171: Update graphemeBreakClass() to classify IndicConjunctBreakExtend
using ranges parsed from DerivedCoreProperties.txt (incbExtendRanges), rather
than all gcb.Extend codepoints; assign the remaining gcb.Extend values the plain
Extend ordinal. Update stringWidth.h and isExtend() to include the new Extend
ordinal while preserving GB9 joining behavior.
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scripts/generate-stringwidth-tables.mjssrc/jsc/bindings/sliceAnsi.cppsrc/jsc/bindings/stringWidth.cppsrc/jsc/bindings/stringWidth.hsrc/jsc/bindings/stringWidthTables.hsrc/jsc/bindings/wrapAnsi.cpptest/js/bun/util/sliceAnsi.test.tstest/js/bun/util/stringWidth.test.tstest/js/bun/util/wrapAnsi.test.ts
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…ngwidth-property-tables
The expected clusters came from Intl.Segmenter, whose Unicode version depends on the platform ICU: on macOS x64 it still treats U+2605 as Extended_Pictographic and joins it to a ZWJ sequence, while the width table follows Unicode 17.
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Problem
Bun.stringWidthdisagrees with the Unicode properties and with string-width on 3,993 of the 1,112,064 scalars, and on common emoji sequences. Examples:"\u20E3"is 2,"🇦"is 1 but"🇦\u0301"is 2,"😀🏻"is 4,"\uFFF9"is 1, 126 unassigned Indic codepoints are 0.isZeroWidth()inscripts/generate-stringwidth-tables.mjs, a hand-kept range list, plus grapheme classes copied from a Unicode 15.1 table (671InCB=Consonantand 689Extended_Pictographicentries differ from 17.0).GraphemeState::width()instringWidth.cppsets the keycap flag on a lone U+20E3 and treats an emoji modifier as a cluster break.console.tableand the markdown renderer size cells withvisibleUTF8Width, which summed code points with no clustering:"👨👩👧"is 2 instringWidthand 6 in a table cell.sliceAnsi.cppcarried its own copy of the cluster width rules.Fix
Controlgrapheme class adds GB4/GB5.GraphemeStatemoves tostringWidth.hand is the one cluster width forstringWidth,sliceAnsiand the UTF-8 path. A keycap needs a[0-9#*]base. A lone regional indicator stays 1 wide, with or without a combining mark after it (string-width agrees). An emoji modifier extends any base (GB9) and never widens it.©and®are emoji bases, so thefirstCpspecial case is gone.visibleUTF8WidthExcludeANSIandutf8IndexAtWidthExcludeANSIwalk grapheme clusters through the same accumulator as the UTF-16 path.wrapAnsi's hard wrap advances by cluster too, so a flag or ZWJ sequence is never split across rows.test/js/bun/util/stringWidth.test.ts(two new describe blocks, 14 tests fail on 1.4.3),sliceAnsi.test.ts,wrapAnsi.test.ts(two new hard-wrap tests, 44 expectations regenerated, every row checked againstcolumns). AlsosliceAnsi-fuzz,stripANSI,wrapAnsi.npm,console-table,bun-inspect-table,test/js/bun/md,markdown-entrypoint,repl: 2260 pass.Background
stringWidthTables.his generated. Runbun scripts/generate-stringwidth-tables.mjsto rebuild it.GraphemeStateaccumulates one cluster and applies the emoji rules (flag pair, keycap, skin tone, ZWJ sequence, VS15/VS16) on top of the sum.Notes
Sweep against the property-derived reference model (node 26.3, ICU 78.3, Unicode 17.0) over all 1,112,064 scalars: 1.4.3 agrees on 99.641%, this branch on 99.987%. The 143 that remain:
The 26 regional indicators are 1, the reference (Emoji_Presentation) and node say 2. Kept at 1 on purpose: string-width returns 1, Improve Bun.stringWidth accuracy and robustness #25447 pinned it, and the existing tests assert it. The fix here is only that a mark after a lone one no longer turns it into 2.
101 Indic spacing vowel signs (Mc) are 0, the reference says 1. Kept on purpose so
"\u0915\u093F"stays one column. glibc 2.41wcwidth()returns 1 for them. A maintainer can flip this by removing one line inisZeroWidth().U+115F, U+3164 (Hangul fillers, 2) and U+FFA0 (1): default-ignorable but East Asian Wide letters. node returns 2, 2, 1.
8 unassigned codepoints in the Hangul Jamo Extended-B block: the reference zero-widths the whole block.
Kirat Rai vowel signs (Unicode 16) have
Grapheme_Cluster_Break=Vbut are letters, so the jamo rule is bounded tocp <= U+D7FF.Sequence sweep (2,707 base x modifier combinations): the remaining differences are the kept conventions above, plus sequences where the reference's own rule is loose (a digit plus ZWJ, a combining mark as the cluster base).
wrapAnsi.test.ts: the 44 changed rows all involve" \u20E3"(space plus keycap, now one column instead of two) or"\u0600 👍🏿"(prepend plus a modifier sequence, now 2 columns instead of 4). A script re-evaluated only the expected column of the table with the new build and assertedBun.stringWidth(row) <= columnsfor every row. The family emoji hard-wrap test changes from one codepoint per row to one row, because a hard wrap now moves whole clusters.Self-review: 4 concerns raised, 4 addressed (cluster-aware
wrapWord, a Prepend before a bulk-counted unit, SIMD ASCII counting on the width-only UTF-8 path, the test table regeneration).The UCD files are not reachable from the CI network. The generator accepts
--ucd <dir>with the five files by base name.Bun__isEmojiPresentationis removed.sliceAnsi.cppwas its only user, and it now reads the Emoji bit throughStringWidth::fusedClassify.[human-review] gate passed · iteration 2 · 9 files touched
fails on main (without fix)
passes on PR (with fix)
diff hotspot
gate history · 1 passed · 0 rejected · iteration 2
evidence per changed file