HTMLStripCharFilter reads a backslash right before a quoted attribute value's closing quote as an escaped quote, so the tag runs on to the next quote of the same kind and the visible text in between is dropped (every quoted attribute since 9.9.0 / GITHUB#11724; on* event attributes since the 2012 JFlex rewrite)
Finding LFV-317Area: analysis / HTMLStripCharFilter (JFlex grammar: SingleQuoted, DoubleQuoted, OpenTagAttribute, EventAttribute)Priority: lowImpact: silent wrong resultsNovelty: new
AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.
What it shows
You strip '<a href="C:\Temp\">folder</a> text after <a href="x">y</a> end' with HTMLStripCharFilter and expect 'folder text after y end', which is what 9.8.0, the HTML parsing rules (Python's html.parser as an independent check) and the same document without the trailing backslash give. Instead main returns 'y end': the scanner reads the backslash and the closing quote as an escaped quote, so the attribute value runs on to the next double quote (the one in href="x"), everything from the first tag to the end of the second tag is treated as one tag, and 'folder text after' is never indexed. No error is raised, and a single-quoted value ending in a backslash loses text the same way.
The test shows that HTMLStripCharFilter drops visible text when a quoted attribute value ends in a backslash (href="C:\Temp\"): the backslash is read as escaping the closing quote, so the tag runs on to the next double quote.
Expected vs actual
Expected folder text y (what 9.8.0 and the fixed grammar give); actual y (expected:<[folder text ]y> but was:<[]y>), with -ea and -da.
Files
Run it
- Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
- Tested on Lucene main 645d4fe14a20 (2026-10-28): reproduced.
- Recorded outcome of run 1 on Lucene main 645d4fe14a20: 1 test(s) run, 1 failed.
- How to read the outcome: a failing test is the finding reproducing (the failure message states expected against actual).
- Seeds: a rerun with the same seed replays the same random choices. Assertions off (-da -dsa -Dtests.asserts=false) is the production-like setting.
# Lucene checkout at the tested commit, built with: ./gradlew --no-daemon assemble (JDK 25)
LUCENE=/path/to/lucene; V=12.0.0-SNAPSHOT
CP=$LUCENE/lucene/core/build/libs/lucene-core-$V.jar
CP=$CP:$LUCENE/lucene/codecs/build/libs/lucene-codecs-$V.jar
CP=$CP:$LUCENE/lucene/test-framework/build/libs/lucene-test-framework-$V.jar
CP=$CP:$LUCENE/lucene/analysis/common/build/libs/lucene-analysis-common-$V.jar
CP=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar # test-framework dependencies (Maven Central)
CP=$CP:junit-platform-console-standalone-6.1.3.jar # JUnit Platform console launcher (Maven Central)
javac -d classes -cp "$CP" $(find src -name '*.java')
# run 1: assertions on, seed DEADBEEF
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
-cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
execute --select-class org.apache.lucene.analysis.charfilter.TestHTMLStripAttributeBackslashGradle alternative: copy the test into the matching module's src/test/ tree of the checkout and run ./gradlew -p lucene/<module> test --tests <class> -Ptests.seed=<seed> (add -Ptests.asserts=false for a run without assertions).
Feedback
Open an issue in lucene-ai-bug-hunt. Please do not open issues or pull requests in apache/lucene about this finding unless a Lucene committer agrees it should be filed.
Snapshot of 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.