Custom Gradle Logging

My company uses Buildkite for our CI services. When the CI server triggers a build, all logs from the build are sent to Buildkite and made available through the UI. This is useful since it allows us to check how a build failed.

Buildkite has a feature which creates collapsible groups from logs formatted like:

--- Compiling
logs after this point will be in a collapsible group named 'Compiling'

--- Testing
logs after this point will be in a collapsible group named 'Testing'

How can I add custom logging to a gradle build which will output these 'groups'? I'd like to have a group for compiling/assembling, one for running unit tests, etc.

I've considered adding tasks which perform the logging and making them dependencies of the built-in tasks, but I'm not sure how to do that, or if it's a good idea in general.

Solution

I'm using Gradle 2.12 and whipped up an example from the Logging doc. The example does not use Android Studio nor BuildKite, but I believe this will help with the fundamental question.

Given a simple build.gradle file for a typical Java project:

apply plugin: 'java'

repositories {
    mavenCentral()
}

dependencies {
    testCompile 'junit:junit:4.11'
}

compileJava << { println "TRACER example log from compileJava" }
compileTestJava << { println "TRACER example log from compileTestJava" }

test << { println "TRACER example log from test" }

and an init.gradle file:

useLogger(new CustomEventLogger())

class CustomEventLogger extends BuildAdapter implements TaskExecutionListener {

    public void beforeExecute(Task task) {
        if (task.name ==~ "compileJava") {
            println "--- Compiling"
        } else if (task.name == "test") {
            println "--- Testing"
        }
    }

    public void afterExecute(Task task, TaskState state) {}

    public void buildFinished(BuildResult result) {}
}

then this command-line:

$ gradle -I init.gradle test

yields this output:

--- Compiling
TRACER example log from compileJava
TRACER example log from compileTestJava
--- Testing
TRACER example log from test