[JSC] Yarr: regenerate the non-unicode /i canonicalization table with the Unicode 16 and 17 case pairs - #456
[JSC] Yarr: regenerate the non-unicode /i canonicalization table with the Unicode 16 and 17 case pairs#456robobun wants to merge 2 commits into
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WalkthroughJavaScriptCore adds Unicode UCS-2 canonicalization mappings for new case pairs. A stress test validates ChangesUnicode case-folding
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LGTM — mechanical regeneration of an auto-generated Unicode case-folding data table, with thorough test coverage.
What was reviewed:
- Verified the offset arithmetic for each new/changed range entry (0x019b+0xa641=0xa7dc, 0x0264+0xa567=0xa7cb, and their RangeHi mirrors; 0x1c89/8a is odd-first so AlternatingUnaligned; 0xa7cc..0xa7db is even-first so AlternatingAligned).
- Confirmed range contiguity is preserved (no gaps/overlaps at the edited boundaries) and the net range count stays at 460 (+1 at 0x1c89, −1 in the merged 0xa7cc..0xa7db block), so
ucs2CanonicalizationRangesneeds no change. - Checked that the merged 0xa7cc..0xa7db AlternatingAligned range preserves the pre-existing A7D0/1 and A7D6..9 pairs, and that the new test exercises those neighbours plus unrelated adjacent code units.
Extended reasoning...
Overview
This PR regenerates Source/JavaScriptCore/yarr/YarrCanonicalizeUCS2.cpp, a committed auto-generated data table that encodes BMP case-equivalence for non-unicode /i regex matching. The file is produced by running YarrCanonicalizeUCS2.js in a JS shell; its last refresh predated Unicode 16, so eight new case pairs from Unicode 16/17 were missing (they were marked CanonicalizeUnique). The diff updates exactly the ranges covering those sixteen code units and adds a comprehensive stress test. No engine logic is touched — only static constinit table data.
Security risks
None. This is pure Unicode case-mapping data consumed by the Yarr interpreter/JIT via canonicalRangeInfoFor() (a binary search over a fixed-size array). The array size constant (ucs2CanonicalizationRanges = 460) is unchanged, the ranges remain sorted and contiguous over 0x0000..0xffff, and no pointers or set indices are added. There is no user-controlled input path into this table beyond ordinary regex compilation, which already handles all range types.
Level of scrutiny
Low-to-moderate. The file is explicitly marked "DO NOT EDIT! - this file autogenerated by YarrCanonicalizeUCS2.js", and the PR states the new content is the unmodified generator output under ICU 78.3, byte-identical across JSC and V8, and exhaustively cross-checked against the ES Canonicalize definition for all 65536 code units. I independently spot-verified every changed row against YarrCanonicalize.h's semantics: the RangeLo/RangeHi deltas resolve to the correct partners, 0x1c89 (odd) correctly uses AlternatingUnaligned, 0xa7cc (even) correctly uses AlternatingAligned, the merged range absorbs the previously-separate A7D0/1 and A7D6..9 pairs without changing their behaviour, and range boundaries stay contiguous. The +1/−1 range-count changes cancel out, matching the unchanged 460 constant.
Other factors
The accompanying test is unusually thorough for a data update: it exercises each new pair bidirectionally as an atom, anchored atom, character class, negated class, embedded atom, backreference, and replace target, under both /i and /iu, with the Yarr JIT on and off, and additionally asserts that neighbouring pre-existing pairs still work and that adjacent unrelated/unassigned code units do not match. The PR description confirms the test passes on V8 and fails on the pre-patch engine at exactly the first new pair. This is a straightforward, well-verified data refresh with no design decisions to weigh.
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Inline comments:
In `@JSTests/stress/regexp-ignore-case-unicode-16-17-case-pairs.js`:
- Line 91: Update the range assertions around the existing test cases so each
match depends on case-insensitive canonicalization: change the U+A7CC–U+A7DB
class to exclude U+A7DB while testing U+A7DB, and change the U+1C80–U+1C8F class
to exclude U+1C8A while testing U+1C8A. Preserve the surrounding shouldBe
assertions and expected true results.
🪄 Autofix
Fix all unresolved CodeRabbit comments on this PR:
- Push a commit to this branch (recommended)
- Create a new PR with the fixes
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JSTests/stress/regexp-ignore-case-unicode-16-17-case-pairs.jsSource/JavaScriptCore/yarr/YarrCanonicalizeUCS2.cpp
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LGTM — mechanical regeneration of an autogenerated data table to match the Unicode 17 case data already used by /iu and ICU.
What was reviewed:
- Verified the new
ucs2RangeInfoentries arithmetically: 0x019B+0xA641=0xA7DC, 0x0264+0xA567=0xA7CB, and the A7CC–A7DBAlternatingAlignedblock correctly absorbs the pre-existing A7D0/1 and A7D6–9 pairs. - Confirmed the ranges remain contiguous and sorted (binary-search invariant for
canonicalRangeInfoFor()) and the net entry count stays at 460 (+1 at 1C89, −1 at A7CB block). - Checked
AlternatingUnalignedfor 1C89/1C8A (odd-first) andAlternatingAlignedfor A7CC–A7DB (even-first) are the right parities. - The one review comment on the test's class-range assertions was addressed in e640512 and is resolved.
Extended reasoning...
Overview
This PR regenerates Source/JavaScriptCore/yarr/YarrCanonicalizeUCS2.cpp, a committed autogenerated file (produced by yarr/YarrCanonicalizeUCS2.js), to pick up the eight BMP simple case pairs added in Unicode 16 and 17. The diff touches ~10 range-table entries and adds a new stress test. No logic, no header changes, no character-set additions — the range count constant ucs2CanonicalizationRanges = 460 is unchanged, so canonicalRangeInfoFor() and every consumer are untouched.
Security risks
None. This is a static constinit lookup table of Unicode case-folding pairs consumed by the Yarr pattern compiler. There is no user-controlled input into the table, no allocation, no bounds computed from these values beyond the existing binary search over a fixed array whose length constant did not change.
Level of scrutiny
Low-to-moderate. The file header says "DO NOT EDIT! - this file autogenerated by YarrCanonicalizeUCS2.js", and the PR is precisely that: re-running the generator under ICU 78.3. This is the moral equivalent of a dependency/data version bump. The correctness bar is "does the regenerated data match Unicode 17", and the PR description documents unusually rigorous verification: byte-identical generator output on JSC and V8, an independent decoder walked over all 65 536 code units against the ES Canonicalize definition (0 diffs, previously 16), and cross-checked against V8's /i. I additionally spot-checked the arithmetic on every changed entry and confirmed the table's structural invariants (sorted, contiguous, correct alternation parity, count preserved).
Other factors
- The only outstanding review comment (CodeRabbit, on two test assertions that trivially passed without folding) was addressed in e640512 and marked resolved by both parties.
- A thorough new stress test covers all eight pairs bidirectionally across atoms, classes, negated classes, backreferences,
replace, and class ranges, plus neighbouring pairs whose ranges were merged/split and adjacent unassigned code points, under both Yarr JIT on and off. - A companion Bun PR (oven-sh/bun#39381) pins this preview build and adds the same checks to Bun's CI, which does run.
- The change brings non-unicode
/iinto agreement with the/iutable (already at 17.0.0 viaucd/CaseFolding.txt) and with V8.
… the Unicode 16 and 17 case pairs YarrCanonicalizeUCS2.cpp is a committed file produced by running YarrCanonicalizeUCS2.js in a JS shell, so it carries the case mappings of whatever ICU that shell had. It was last regenerated before the Unicode 16 data existed, while the /iu table (YarrCanonicalizeUnicode.cpp) is generated at build time from ucd/CaseFolding.txt, which is at 17.0.0. As a result the eight BMP simple case pairs added in Unicode 16 and 17 (U+019B/U+A7DC, U+0264/U+A7CB, U+A7CC/U+A7CD, U+A7CE/U+A7CF, U+A7D2/U+A7D3, U+A7D4/U+A7D5, U+A7DA/U+A7DB, U+1C89/U+1C8A) are CanonicalizeUnique under /i but fold under /iu and in String.prototype.toUpperCase. This is the unmodified output of YarrCanonicalizeUCS2.js run under ICU 78.3 (Unicode 17). The only entries that change are the ones for those sixteen code units; the character sets, the range count and the Latin-1 table are unchanged.
The tested character now lies outside each range, so the assertions only pass when the range's partner is canonicalized into the class.
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Beyond the inline nit, I also checked the table invariants the binary search in canonicalRangeInfoFor() depends on: the modified ranges stay sorted and gap-free (0x1c88→0x1c89-8a→0x1c8b-8f→0x1c90 and 0xa7ca→0xa7cb→0xa7cc-db→0xa7dc→0xa7dd-f4), the net entry count is unchanged so ucs2CanonicalizationRanges = 460 still matches the initializer, the new RangeLo/RangeHi offsets check out arithmetically (0x019b+0xa641=0xa7dc, 0x0264+0xa567=0xa7cb), and the alternating-range parities are correct (0x1c89 odd → Unaligned, 0xa7cc even → Aligned).
Extended reasoning...
The only reported finding is a test-convention nit (testLoopCount vs hardcoded 50), which does not affect correctness. I'm not auto-approving because this is a user-visible change to core /i regex semantics in JavaScriptCore, so a maintainer should sign off on shipping the Unicode 16/17 data bump — but the data change itself is mechanical and I verified the structural invariants above so a human reviewer need not re-derive them.
| [0xa64b, 0xa64a], // CYRILLIC LETTER MONOGRAPH UK (also equivalent to U+1C88 below) | ||
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| for (let i = 0; i < 50; ++i) { |
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🟡 Nit: JSTests/README.md (rule #2, imported by JSTests/CLAUDE.md) requires new tests to use testLoopCount for the iteration count so the harness can tune it per configuration — under //@ runNoJIT the fixed 50 iterations are wasted, and other configs may want a different tier-up count. Since the PR notes this file also runs on V8, guard it: for (let i = 0; i < (typeof testLoopCount !== "undefined" ? testLoopCount : 50); ++i).
Extended reasoning...
What this is
JSTests/README.md line 20 (which JSTests/CLAUDE.md pulls in via @README.md) states that new tests are required to:
Use
testLoopCountorwasmTestLoopCountto control how many iterations a test runs. ThejscCLI sets these based on the configuration of the test, so tests iterate enough to tier up where that matters and exit early where it doesn't.
The new test at JSTests/stress/regexp-ignore-case-unicode-16-17-case-pairs.js:66 instead uses a hardcoded loop bound:
for (let i = 0; i < 50; ++i) {This is the repository's stated convention for new stress tests (2000+ existing files under JSTests/stress use testLoopCount), so flagging it here even though it has no functional effect on what the test verifies.
Why it matters (mildly)
This test declares two configurations at the top:
//@ runDefault("--useRegExpJIT=true")
//@ runNoJIT("--useRegExpJIT=false")Under runNoJIT, nothing tiers up, so 50 iterations of the full pair/neighbour/unrelated battery just repeat the same interpreter path 50× for no additional coverage — pure wasted wall-clock in a suite whose README also asks tests to stay under 200ms per configuration. Under runDefault, 50 may or may not line up with the Yarr/baseline tier-up thresholds the harness would otherwise pick. testLoopCount exists precisely so the harness can set the count high where tier-up matters and low (or 1) where it doesn't.
Step-by-step
run-jsc-stress-testslaunches therunNoJITconfiguration and injects a smalltestLoopCount(since JIT is disabled, extra iterations add nothing).- The test ignores that value and runs the outer loop 50 times anyway.
- Each iteration executes 8 new pairs × 2 flag sets × 2 directions × 7 assertions, plus 8 neighbouring pairs × the same, plus the U+1C88 and 7
checkUnrelatedchecks — several thousandRegExpconstructions and matches per iteration, ~50× more work than the harness asked for in that configuration. - Under
runDefault, if the harness would have chosen atestLoopCounthigher than 50 to guarantee tier-up of the compiled patterns, the hardcoded 50 may undershoot instead.
Neither of these makes the test wrong — the assertions still cover the fix and fail on the old table — it just doesn't let the harness tune the cost/coverage trade-off the way the README requires.
Why the guard
The PR description says the test "passes on V8 as written," and V8's d8 shell does not define testLoopCount. A bare for (let i = 0; i < testLoopCount; ++i) would throw ReferenceError there. Guarding with typeof testLoopCount !== "undefined" ? testLoopCount : 50 keeps the file portable to V8 while honouring the JSTests convention under jsc.
Suggested fix
for (let i = 0; i < (typeof testLoopCount !== "undefined" ? testLoopCount : 50); ++i) {Severity: nit — this is a test-suite convention for new tests, not a correctness issue; the test already validates the table change correctly.
…and 17 Picks up oven-sh/WebKit#456, which regenerates JavaScriptCore's committed /i canonicalization table (yarr/YarrCanonicalizeUCS2.cpp) under ICU 78. The /iu table is built from CaseFolding.txt 17.0.0 at build time, so the eight BMP case pairs added in Unicode 16 and 17 folded under /iu but not under /i. Pinned to the preview build of that PR for now. The test covers the eight pairs in both directions under /i and /iu, the neighbouring pairs whose table runs were merged or split, the code units around them, class ranges, and the Yarr interpreter.
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Problem
Non-unicode
/idoes not fold the eight BMP simple case pairs added in Unicode 16 and 17, while/iuandString.prototype.toUpperCase(ICU 78) do, and V8 folds them under/i:Pairs: U+019B/U+A7DC, U+0264/U+A7CB, U+A7CC/U+A7CD, U+A7DA/U+A7DB, U+1C89/U+1C8A (Unicode 16), U+A7CE/U+A7CF, U+A7D2/U+A7D3, U+A7D4/U+A7D5 (Unicode 17). All sixteen code units are
CanonicalizeUniqueinSource/JavaScriptCore/yarr/YarrCanonicalizeUCS2.cpp.Cause: the two
/imodes get their tables differently.YarrCanonicalizeUnicode.cpp(/iu) is generated at build time fromucd/CaseFolding.txt, which is at 17.0.0 (CMakeLists.txt:2111).YarrCanonicalizeUCS2.cpp(/i) is a committed file produced by runningyarr/YarrCanonicalizeUCS2.jsin a JS shell, so it holds the case mappings of whatever ICU that shell had; its last data refresh predates the Unicode 16 mappings.Tools/Scripts/update-ucdonly refreshesucd/*.txt, so the 16.0.0 and 17.0.0 UCD updates did not touch it. Upstream WebKit main has the same stale table.Fix
YarrCanonicalizeUCS2.cppis replaced with the unmodified output ofYarrCanonicalizeUCS2.jsrun under ICU 78.3 (Unicode 17). The diff is the sixteen code units above: U+019B/U+A7DC and U+0264/U+A7CB becomeRangeLo/RangeHipairs, U+1C89/U+1C8A an unaligned alternating pair, and U+A7CC..U+A7DB one aligned alternating range (it absorbs the existing U+A7D0/1 and U+A7D6..9 pairs). Character sets, the range count (460) andlatin1CanonicalizationTableare unchanged, socanonicalRangeInfoFor()and its users need no change.YarrCanonicalize.hdoes) gives, for every one of the 65536 code units, the same equivalence set as the ESCanonicalizedefinition evaluated with ICU 78 (0 differences; the previous table had 16), and V8's/iaccepts every pair the table encodes. Against the current engine, exactly the 16 new directions are rejected and nothing else changes.JSTests/stress/regexp-ignore-case-unicode-16-17-case-pairs.jschecks the eight pairs in both directions as an atom, in a class, in a negated class, inside a longer atom, as a backreference and inreplace, under/iand/iu, plus the neighbouring pairs whose ranges were merged or split (U+019A/U+023D, U+0263/U+0194, U+0265/U+A78D, U+A7D0/1, U+A7D6/7, U+A7D8/9, U+A7F5/6, U+1C88 with U+A64A/B), the unassigned or unrelated code units next to the new entries, and class ranges that contain one half of a pair while the tested character lies outside the range. It runs with the Yarr JIT on and off. It passes on V8 as written, and on the preview build of this PR with the Yarr JIT on and off; on the current engine it fails at its first assertion (U+19b/U+a7dc /i atom: expected true but got false), and with the new pairs removed it fails at the first class range assertion while the neighbouring-pair and unrelated assertions pass, so those describe behaviour this change keeps.c6cfe90c60, the commit Bun pins today, so the preview build is that commit plus this change. Bump WebKit (oven-sh/WebKit#456 preview): non-unicode /i folds the case pairs added in Unicode 16 and 17 bun#39381 pins the preview build of this PR and adds the same checks to Bun's test suite (neither repo's CI runs JSTests); its test fails 10 of 39 cases on the current engine and passes against this build, and a sweep of Bun's/iover the whole BMP against the ESCanonicalizedefinition under ICU 78 goes from 16 differences to 0.Background
/i(ESCanonicalizewithout theuflag) compares code units after mapping each one withtoUpperCase, keeping it unchanged when the result is not a single code unit or when a non-ASCII character would map into ASCII./iuuses simple case folding (CaseFolding.txt) instead. Yarr precompiles both relations into range tables: each BMP range says whether its code units are unique, form a pair at a fixed distance (RangeLo/RangeHi), form consecutive pairs (AlternatingAlignedfor even/odd pairs,AlternatingUnalignedfor odd/even), or belong to a listed set of three or more;canonicalRangeInfoFor()binary-searches them.update-ucdbrought the/iuand property data to 17.0.0; the/itable is the one piece of case data that is not derived fromucd/at build time.