mruby-regexp: test the F4 upper bound of the four-byte UTF-8 range - #7072
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`mrb_re_utf8_charlen()` rejects a four-byte sequence that spells a codepoint past U+10FFFF by narrowing the first continuation byte to `0x80` through `0x8f` when the lead byte is `F4`. Nothing exercised that narrowing. The nearest existing case, `"\xF5\x80\x80\x80"`, carries a lead byte outside the four-byte range entirely, so it returns before any continuation byte is looked at. Add `"\xF4\x90\x80\x80"`, the shortest spelling of U+110000. It takes the `F4` branch and scans as four separate bytes.
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📝 WalkthroughWalkthroughThe regexp test suite adds a regression assertion for the invalid UTF-8 sequence ChangesRegexp UTF-8 regression
Estimated code review effort: 1 (Trivial) | ~2 minutes Possibly related PRs
Suggested reviewers: 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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This was referenced Aug 12, 2026
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Follow-up to #7068.
mrb_re_utf8_charlen()rejects a four-byte sequence that spells a codepoint past U+10FFFF by narrowing the first continuation byte to0x80through0x8fwhen the lead byte isF4. Nothing exercised that narrowing. The nearest existing case,"\xF5\x80\x80\x80", carries a lead byte outside the four-byte range entirely, so it returns before any continuation byte is looked at.Add
"\xF4\x90\x80\x80", the shortest spelling of U+110000. It takes theF4branch and scans as four separate bytes.Test only, no behavior change.
Summary by CodeRabbit
F4 90 80 80is processed as four separate bytes rather than a single character.