apache/kafka · error · GradleException

No project JARs configured on…

Error message

No project JARs configured on kafkaPublicApiChecker.projectJarFiles — the checker needs at least one classes/jar source to build the API surface.

What it means

GradleException from KafkaPublicApiCheckerTask.checkPublicApi when projectJarFiles is empty. The checker needs at least one classes/jar source to build the API surface to compare against the javadoc jar. Empty input would yield a meaningless result, so it fails fast.

Solutions

  1. Configure the input: kafkaPublicApiChecker.projectJarFiles.from(tasks.named('jar')) or from the runtime/compile configuration of the module.
  2. Add dependsOn('jar') so the project jar exists at check time.
  3. If checking multiple modules, from(subprojects.collect { it.tasks.named('jar') }).
  4. If the module genuinely produces no jar, disable the task (enabled = false) rather than leaving it misconfigured.

Example fix

// before
kafkaPublicApiChecker {
  javadocJarPath = ...
  // projectJarFiles not set -> empty -> hard fail
}
// after
kafkaPublicApiChecker {
  javadocJarPath = tasks.named('javadocJar').flatMap { it.archiveFile }
  projectJarFiles.from(tasks.named('jar'))
}
Defensive patterns

Strategy: validation

Validate before calling

// In build.gradle
tasks.named('kafkaPublicApiChecker').configure {
  dependsOn 'jar'
  doFirst {
    assert !projectJarFiles.files.empty: 'kafkaPublicApiChecker.projectJarFiles is empty; wire tasks.named("jar")'
  }
}

Prevention

When it happens

Trigger: projectJarFiles.getFiles().isEmpty() is true at line 88, inside the try block after the javadoc jar exists. Happens when the build script never sets kafkaPublicApiChecker.projectJarFiles, or sets it from a configuration that resolves to no artifacts.

Common situations: Applying the plugin without configuring projectJarFiles; pointing it at a configuration that is empty for the current variant; applying in a meta-module that produces no jar; the producing task has not run yet (no dependsOn).

Related errors

AI-assisted analysis of apache/kafka@996fb4585a (2026-08-11). Data as JSON: /api/errors/59248298df5f7264. Report an issue: GitHub.

Appendix: source

Thrown at api-checker/gradle-plugins/src/main/java/org/apache/kafka/gradle/KafkaPublicApiCheckerTask.java:89

    @TaskAction
    public void checkPublicApi() {
        if (!getCheckerEnabled().get()) {
            getLogger().info("KafkaPublicApiChecker is disabled, skipping...");
            return;
        }

        File jarFile = getJavadocJarFile();
        if (!jarFile.exists()) {
            throw new GradleException("Javadoc JAR file not found: " + jarFile.getAbsolutePath() +
                ". Make sure the javadoc task has run first.");
        }

        getLogger().info("Checking public API consistency in: {}", jarFile.getAbsolutePath());

        try {
            if (projectJarFiles.getFiles().isEmpty()) {
                throw new GradleException(
                        "No project JARs configured on kafkaPublicApiChecker.projectJarFiles — "
                        + "the checker needs at least one classes/jar source to build the API surface.");
            }
            PublicApiChecker checker = new PublicApiChecker(
                new ArrayList<>(projectJarFiles.getFiles()),
                new ArrayList<>(referenceJarFiles.getFiles()));
            CheckResult result = checker.checkPublicApiConsistency(jarFile);
            List<PublicApiViolation> violations = result.violations();
            List<PublicApiViolation> suppressions = result.suppressions();

            // Generate report
            ViolationReporter reporter = new ViolationReporter();
            File report = reportFile.get().getAsFile();
            reporter.writeTextReport(violations, suppressions, report);

            // Print summary to console
            reporter.printToConsole(violations, suppressions);

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