Jenkins Workflow: Executing build step for every change in commit

At work, we wanted send an email for every change that was made in a project. By default, Jenkins likes to collate changes into as few builds as possible, and normally sends an email per build.

The solution seemed to be usage of Jenkins Pipeline. Jenkins Pipeline enables creation and execution of jobs "on the fly" as needed.

First problem was to get access to ChangeLogSet. There is some preset variables in Jenkinsfile, but I could not find documentation for them. After some googling, Stack Overflow came to rescue.

def changes = currentBuild.rawBuild.changeSets

But when this was executed, Jenkins complained

org.jenkinsci.plugins.scriptsecurity.sandbox.RejectedAccessException: Scripts not permitted to use method org.jenkinsci.plugins.workflow.support.steps.build.RunWrapper getRawBuild

There's a "In-process Script Approval" -tool in Jenkins, where you can allow usage of these methods.

After that was solved, next problem was with serialization. As the actual job execution is transferred to different node, every non-serializable object caused an exception. To prevent this, I had to null objects in proper places. This then prevented running jobs in loop, as the variables in loops needed to be nulled before job execution. So I had to collect jobs into map, and after every job was defined, null everything and use "parallel" -task to execute jobs.

So the whole thing is here:

//changes is http://javadoc.jenkins-ci.org/hudson/scm/ChangeLogSet.html
def changes = currentBuild.rawBuild.changeSets
//We need to create branches for later execution, as otherwise there would be serialization exceptions
branches = [:]
for (int j = 0; j < changes.size(); j++) {
    def change = changes.get(j)
    for (int i = 0; i < change.getItems().size(); i++) {
        def entry = change.getItems()[i]
        def commitTitleWithCaseNumber = entry.getMsg()
        def commitMessage = entry.getComment()
        //split from first non digit
        def caseNumber = (commitTitleWithCaseNumber =~ /^[0-9]*/)
        // check that caseNumber was in case place
        if( !caseNumber[0].isEmpty() && commitTitleWithCaseNumber.startsWith(caseNumber[0])) {
          // Remove number from title, just for nicer subject line
          def commitTitle = commitTitleWithCaseNumber.substring(caseNumber[0].length()).trim()
          def number = caseNumber[0]
          branches["mail-${j}-${i}"] = {
              node {
                  emailext body: commitMessage, subject: "[Sysart ${number}] ${commitTitle}", to: 'redacted@example.com'
             }
          }
        }
        // Need to forcibly null all non serializable classes
        caseNumber = null
        entry = null
    }
    change = null
}
changes = null
stage 'Mail'
parallel branches

This was a little more difficult that I had expected, mainly because of serialization complications. But in the end, it works so it cannot be completely stupid.