This message was deleted.

You can add a

TaskExecutionGraphListener

to

project.getGradle().getTaskGraph()

and check for the presence of both tasks in the task execution graph. But first make sure it's compatible with configuration cache (https://docs.gradle.org/current/userguide/configuration_cache.html#config_cache:requirements:build_listeners is not clear to me)

I guess for example by having a shared build service

An alternative maybe could "just" be to declare that the check task must be run before the dump task? `dumpTask.mustRunAfter(checkTask)`; that way the check task cannot falsely detect the output of the dump task (you don't have a custom error message though)

Now I am sure, it is CC safe. So simply this:

gradle.taskGraph.whenReady {
    check(!(hasTask("a") && hasTask("b"))) {
        "Task 'a' and 'b' cannot be executed together."
    }
}