Affects Version/s: 3.3.9, needing-scrub-3.4.0-fallout
Fix Version/s: 4.x / Backlog
Environment:Linux 4.2.0-23-generic #28-Ubuntu SMP Sun Dec 27 17:47:31 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
I have found an issue with respect to the MojoExecutor in maven-core when building with multiple threads (e.g. -T1C).
I have created a small reproduction project here: https://github.com/fvanderveen/maven-mojo-jojo (in the readme is some more explanation of what I found to be the problem)
The reproduction, using the above code:
1. Clone this repository (`git clone https://github.com/fvanderveen/maven-mojo-jojo.git`)
2. Make sure the clone works single-threaded: `mvn clean package`. (This should succeed)
3. Clean the workspace (`mvn clean`)
4. Attempt multi-threaded compilation with at least 2 threads (`mvn package -T2`)
Boiled down, it seems like the MojoExecutor#ensureDependenciesAreResolved will cause an invocation to LifecycleDependencyResolver#resolveProjectDependencies for all projects in the current MavenSession if it's configuring a plugin that defines @Mojo(aggregator = true) and DependencyContext#isResolutionRequiredForAggregatedProjects return true.
This resolving may, if triggered at an unfortunate time, override resolved artifacts for projects that are being built concurrently.
In our case, a test-compile execution of the maven-compiler-plugin was just configured (setting the resolved artifacts to the test-scope artifacts), and right before its execution, the resolved artifacts got set back to the compile-scope artifacts due to a aggregator plugin being configured at around the same time.
Given the way the `ensureDependenciesAreResolved` is structured and what aggregator plugins should do/depend on, I think it would make more sense to only invoke LifecycleDependencyResolver#resolveProjectDependencies for the modules that are a (grand-)child of the current project.
I've created a maven extension (which can be placed in lib/ext) as a temporary workaround using said change; which may be found here if any one else is having the same problems: https://github.com/fvanderveen/maven-non-destructive-mojo-executor