Write native configuration file when only lambda hints are present

[junhyeong9812]

Overview

FileNativeConfigurationWriter fails to write reachability-metadata.json when a RuntimeHints instance contains only lambda hints, silently dropping the lambda metadata.

Problem

NativeConfigurationWriter.write(RuntimeHints) only writes the configuration file when hasAnyHint(hints) returns true:

public void write(RuntimeHints hints) {
	if (hasAnyHint(hints)) {
		writeTo("reachability-metadata.json",
				writer -> new RuntimeHintsWriter().write(writer, hints));
	}
}

However hasAnyHint(hints) does not check ReflectionHints.lambdaHints():

private boolean hasAnyHint(RuntimeHints hints) {
	return (hints.proxies().jdkProxyHints().findAny().isPresent() ||
			hints.reflection().typeHints().findAny().isPresent() ||
			hints.resources().resourcePatternHints().findAny().isPresent() ||
			hints.resources().resourceBundleHints().findAny().isPresent() ||
			hints.jni().typeHints().findAny().isPresent() ||
			hasAnyDeprecatedHint(hints));
}

RuntimeHintsWriter already serializes lambda hints (see the oneLambda test in RuntimeHintsWriterTests), so when a RuntimeHints holds only lambda hints registered via ReflectionHints.registerLambda(...), hasAnyHint returns false, the file is never written, and the lambda metadata is lost. This is not caught on the JVM; it only surfaces as a native-image runtime failure.

Fix

Include lambda hints in hasAnyHint() so the configuration file is written whenever lambda hints are present:

hints.reflection().lambdaHints().findAny().isPresent() ||

Adds a lambdaConfig() test that registers only a lambda hint and asserts the file is written with the expected JSON. Without the fix the test fails with NoSuchFileException because no file is produced.

[sbrannen]

Good catch! 👍

This is effectively a bug that was introduced when the support for lambda hints was added in 7.0.6.

• Allow registering serialized lambda metadata through RuntimeHints #36339

[junhyeong9812]

Thank you for the review and merge, @sbrannen. Thanks to your work, I get to use a great framework every day. I really appreciate it.

[sbrannen]

@junhyeong9812, you're very welcome, and thanks for the kinds words!