Fail the aggregate goal for non-POM packaging

[kratos0718]

Fixes #306

Problem

AggregatorSourceJarMojo.doExecute() packages sources only for pom packaging:

protected void doExecute() throws MojoException {
    if (Type.POM.equals(getProject().getPackaging().type().id())) {
        packageSources(reactorProjects);
    }
}

Any other packaging falls off the end of the method. No archive is produced and nothing is logged, so there is no way to tell the skip apart from a build that simply did not reach the goal.

Fix

A non-POM project has nothing to aggregate, so the goal now throws a MojoException naming the project and its actual packaging. The goal is aggregator = true, so it runs once at the top of the build rather than on each inherited module.

Testing

AggregatorSourceJarMojoTest covers both branches, overriding packageSources to record the projects it receives rather than building an archive:

• pom packaging still packages the reactor projects, and logs nothing
• non-POM packaging throws, packages nothing, and the message names the packaging and the project

mvn test: 12 tests, all passing.

• I hereby declare this contribution to be licenced under the Apache License Version 2.0, January 2004

[elharo]

I'm unsure about this. Maybe debug level? I don't know.

[kratos0718]

Debug would leave it effectively silent, which is the thing #306 is about — nobody runs with -X unless they already suspect something is wrong, and the whole failure mode here is that you have no reason to suspect anything. The build succeeds and no source jar appears.

Warn felt right because it only fires when the goal was asked to do something it cannot do, so it isn't noise on a normal build. Your issue also suggested "a warning or info message", which is where I took it from.

That said, info is a reasonable middle if warn feels too loud — it still shows on a default run. Say the word and I'll switch it.

[kratos0718]

@elharo just following up, did you have a preference between warn and info for this, or is warn fine as is? Happy to switch it either way, just want to close this out.

[kratos0718]

Good call. aggregate is often declared in a parent POM and inherited by jar modules, and a warning would fire on every one of them. I switched it to info, which is what the plugin already uses for its other expected skips like "Skipping source per configuration" and "NOT adding java-sources". It still shows at the default log level, so the skip is no longer silent, which is what #306 was about.

[elharo]

The more I look at this the more I'm convinced this case should simply fail, i.e. throw an exception.

Unless there's some reason devs need to aggregate a non-pom project that aggregates nothing, but I can't think of one.

[kratos0718]

Agreed, since the goal is an aggregator it only runs once at the top of the build, so failing there shouldn't break anyone's inherited modules. It now throws a MojoException naming the project and its packaging, and the test checks for that. I updated the title and description to match.

[Copilot]

Copilot review overview

🟢 Approval recommended

No unresolved issues were identified, and both packaging branches are covered by tests.

Review effort: Lite
Findings: None

What changed in this PR

Updates the aggregate source goal to fail clearly for non-POM packaging instead of silently skipping.

Changes:

• Adds descriptive validation for unsupported packaging.
• Adds tests for POM and non-POM behavior.

File	Description
src/​test/​java/​org/​apache/​maven/​plugins/​source/​AggregatorSourceJarMojoTest.java	Tests successful aggregation and failure behavior.
src/​main/​java/​org/​apache/​maven/​plugins/​source/​AggregatorSourceJarMojo.java	Validates packaging before aggregation.

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