mruby-regexp: ask the backward search about a long multibyte subject - #7234
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Included review availability: Your plan includes up to 8 reviews per rolling hour; 4 remain after this review. 📝 WalkthroughWalkthroughAdded UTF-8 regression tests for backward searches on long multibyte strings. The tests cover ChangesUTF-8 backward search coverage
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: 🔵 Low · up to This test-only change expands UTF-8 backward-search coverage for long subjects and byte offsets. It is mergeable with owner awareness of the bounded concern that one byte-offset assertion may not directly exercise an interior multibyte window. Suggested reviewers: 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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In `@mrbgems/mruby-regexp/test/string_index.rb`:
- Around line 460-461: Update the rindex assertion around the overlapping-match
test to use three consecutive “あ” characters, so /ああ/ matches at overlapping
positions, and expect the last match index to be 1 while preserving the trailing
filler.
- Around line 463-469: Update the mb.byterindex assertion in the string indexing
tests to use an interior UTF-8 byte offset such as 4 or 5 instead of 3, and
assert that it raises IndexError.
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The backward search of `rindex`, `byterindex` and `rpartition` (mruby#7233) has two paths: a window at the end of the subject, and a forward search over the whole of it for what the window cannot reach. Which one answers depends on how far the last match is from the end, and the tests that came with it ask each of them on the subjects it takes to reach them, but only in ASCII. The multibyte tests beside them use subjects of a few characters, which every window covers, so the second path has never been asked about a character at all. Ask it. `"あい" + "うえ" * 2000` is 4,002 characters and 12,006 bytes, and its one `あい` is at the front, past the reach of any window; `え` and `うえ` are at the end, within the first. Both are asked in both spaces, along with the miss, the overlapping match, `rpartition`, and the positions the pair reads differently. The subject is also what puts a window start inside a character: the window is measured in bytes and widened by doubling, so on this subject most of the starts it takes are interior ones, which the engines step over rather than seed an attempt at. Green as it stands, and green with the window's span bound compiled as 0, which sends every one of these through the forward search, and as 100,000,000, which sends every one of them through the window: what the two paths answer here is the same.
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Follow-up to #7233, test only.
The backward search that landed there has two paths. A window at the end of the
subject answers a match near the end; a match further in is left to a forward
search over the whole range, which the window falls through to once it would
read more than a fixed span. The tests that came with it ask each path on the
subjects it takes to reach it, but the subjects are ASCII. The multibyte tests
beside them use a few characters each, which one window covers whole, so the
second path has never been asked about a character.
This adds a subject that reaches it.
"あい" + "うえ" * 2000is 4,002characters and 12,006 bytes:
えandうえare at the end, inside the first windows, and are asked inboth spaces:
mb.rindex(/うえ/)is 4,000 andmb.byterindex(/うえ/)is12,000.
あいis at the front, past the reach of any window, so it is theforward search that answers:
mb.rindex(/あい/)andmb.byterindex(/あい/)are both 0,
mb.rpartition(/あい/)splits there, andmb.rindex(/お/)isthe miss.
("あああ" + "い" * 3000).rindex(/ああ/)is 1, the later of the twooverlapping matches at that same end.
mb.rindex(/うえ/, 1)is nil wheremb.rindex(/うえ/, 2)is 2, andmb.byterindex(/うえ/, 3)is nil wheremb.byterindex(/うえ/, 6)is 6.The subject is also what puts a window start inside a character. The window is
measured in bytes and widened by doubling, so on a subject of three-byte
characters most of the starts it takes are interior ones; the engines step over
those rather than seed an attempt at them, and this is the first test where the
window does it more than a couple of times.
The block carries the
__ENCODING__guard the character-bounds test beside itcarries, and sits in its own
assertso that the guard does not swallowassertions that hold on every build.
Verification
Every answer above matches CRuby 4.0.6.
rake test,build_config/ci/gcc-clang.rb:full-debugbintestbintest(bintest suite)cxx_abibyte-stringascii-casebyte-stringis the build that skips it, having noMRB_UTF8_STRING.Green also with
RE_RSEARCH_PROBE_SPANcompiled as0, which sends every oneof these through the forward search, and as
100000000, which sends every oneof them through the window: what the two paths answer on this subject is the
same.
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