Dynamically configuring a task in a parent build.gradle - gradle

Question

I have a multi-project C++ Gradle build, which produces a number of libraries and executables. I'm trying to get the executables (but not the libraries) subprojects to get compiled in with a 'fingerprint' object. This works fine if I sprinkle smth like this in individual subprojects' build.gradle:
compileMain.doFirst {
// code to generate a 'BuildInfo.cpp' from from a template.
// embeds name of executable in so has to be generated anew for each exe
}
Following DRY principles, I'd much rather do this once and for all in a top level build.gradle. This is my attempt, to apply it to just the subprojects that use the cpp-exe plugin, following these instructions:
configure(subprojects.findAll { it.plugins.hasPlugin('cpp-exe') }) {
compileMain.doFirst {
// same code as above
}
}
Alas, this doesn't get triggered. However, if I put smth like this in a less restrictive configure, block, this demonstrates that the idea of querying the plugin should work:
configure(subprojects.findAll { true }) {
task mydebug << {
if ( project.plugins.hasPlugin( 'cpp-exe' ) ) {
println ">>> $project.name has it!"
}
}
}
Could it be that the plugins don't get applied to the subprojects at the time the configure closure is evaluated (in the top-level build.gradle)? There may well be a much simpler way of achieving this altogether?

Answer 1

You probably apply the cpp-exe plugin in the child projects' build scripts. By default, a parent build script gets evaluated before its children, which explains why it's not finding any projects that have cpp-exe applied.
There are several ways to solve this problem. One way is to move all configuration that's specific to a cpp-exe project (like applying the plugin and adding the action) to the same spot. Either you do all such configuration from the parent build script (for example by enumerating the cpp-exe subprojects and configuring them with a single configure(cppExeProjects) { ... }), or you move the cpp-exe specific configuration into its own build script (say gradle/cpp-exe.gradle) and apply it from selected subprojects like so: apply from: "$rootDir/gradle/cpp-exe.gradle".
Another solution is to change the evaluation order of build scripts. But I would only use this as a last resort, and it is certainly not necessary here.

Answer 2

Gradle 1.5 is recently out, I am not sure if this is a new feature but as it looks, you can solve the issue by using afterEvaluate.
Take a look at section 53.6.1 in http://www.gradle.org/docs/current/userguide/build_lifecycle.html
Something like:
subprojects {subProject ->
afterEvaluate {
if ( subProject.plugins.hasPlugin('cpp-exe')){
println "Project $subProject.name has plugin cpp-exe"
}
}
}
would give you a start.