Project dependency evaluation issue

I feel like I’m missing something trivial but can’t figure out what’s wrong. I have a multi-module build like this:

rootBuildFile << """
"""

sharedBuildFile << """
    apply plugin: 'java'            
"""

serverBuildFile << """
    apply plugin: 'java'            

    dependencies {
        compile project(":shared")
    }

    task sourceJar(type: Jar) {
        from sourceSets.main.allJava                
        configurations.compile.dependencies.each {
            from files(it.dependencyProject.sourceSets.main.allSource)
        }
    }
    
"""

rootSettingsFile << """
    include 'shared', 'server'
"""

Basically, I have root module and two submodules where :server needs :shared. I want to create a task that will build an uber-jar with sources from both projects. The issue is this setup fails during project evaluation with Could not get unknown property 'sourceSets' for project ':shared' which means :shared was not evaluate yet at the point it’s accessed and java plugin was not applied yet. Placing the task into afterEvaluate {} does not help and only defers the issue until configuration phase: A problem occurred configuring project ':server'. Applying java in subprojects helps but creates an expectation that either every subproject is java-based, or would require filtering and knowledge about specific subprojects in a root one which is suboptimal.

Is there any way to have it evaluated/configured before that?

Playing with evaluationDependsOn(...) to see if it results into something with a more complex real scenario…