XML query parser: a <Clause> without the occurs attribute, which LuceneCoreQuery.dtd and BooleanQueryBuilder's own code default to SHOULD, is rejected with ParserException 'Invalid value for "occurs" attribute of clause:' (regression since 5.1.0, LUCENE-6270)
Finding LFV-361Area: queryparser / xml (BooleanQueryBuilder)Priority: lowImpact: wrong errorNovelty: 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 give the XML query parser (CoreParser.parse) a <BooleanQuery> whose <Clause> has no occurs attribute and expect an optional (SHOULD) clause, because LuceneCoreQuery.dtd declares occurs with the default "should", BooleanQueryBuilder.getOccursValue has its own 'attribute absent -> SHOULD' branch, and 5.0.0 and earlier parsed it that way. Instead the whole parse fails with ParserException 'Invalid value for "occurs" attribute of clause:' (nothing after the colon): org.w3c.dom.Element.getAttribute returns an empty string, never null, for an absent attribute, so the 'occs == null' default branch never runs; an explicit occurs="" is rejected the same way. Explicit should, must, mustNot and filter values work as before, and writing occurs="should" is a workaround.
The test shows that CoreParser.parse rejects <BooleanQuery fieldName='f'><Clause><TermQuery>a</TermQuery></Clause></BooleanQuery>, a <Clause> without occurs.
Expected vs actual
Expected: one SHOULD clause f:a (the DTD default and the builder's own null branch); actual (-ea and -da): ParserException 'Invalid value for "occurs" attribute of clause:' (BooleanQueryBuilder.java:81), because Element.getAttribute returns "" and the occs == null check (:72) never matches.
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/facet/build/libs/lucene-facet-$V.jar
CP=$CP:$LUCENE/lucene/queries/build/libs/lucene-queries-$V.jar
CP=$CP:$LUCENE/lucene/queryparser/build/libs/lucene-queryparser-$V.jar
CP=$CP:$LUCENE/lucene/sandbox/build/libs/lucene-sandbox-$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.queryparser.xml.TestClauseDefaultOccursThe module(s) facet also need their third-party runtime jars; ./gradlew -p lucene/<module> dependencies lists them.
Gradle 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.