Unexpected behavior instantiating a class from dynamically loaded library

[Hari Krishna Dara]

I have a git project docker-build with the below class:

$ cat src/docker_build/DockerBuild.groovy

package docker_build

class DockerBuild {

    def image

    def steps

    

    DockerBuild(steps) {

        this.steps = steps

        steps.docker.withRegistry('...', '...') {

            image = steps.docker.image('...')

            image.pull()

        }

    }

}

I tried to use the above class from a pipeline like this:

docker_build_lib = library(identifier: 'docker_build@master',

                        retriever: modernSCM( [$class: 'GitSCMSource', remote: '...', credentialsId: '...']))

docker_build = docker_build_lib.docker_build

pipeline {

    agent "any"

    stages {

        stage("Init") {

            steps {

                script {

                    d = docker_build.DockerBuild.new(this)

                    echo "GOT: ${d}"

                }

            }

        }

    }

}

The output I get is something like this:

$ docker login -u "..." -p ******** ...

Login Succeeded

[Pipeline] {

[Pipeline] echo

in withRegistry closure

[Pipeline] }

[Pipeline] // withDockerRegistry

[Pipeline] }

[Pipeline] // withEnv

[Pipeline] echo

GOT: org.jenkinsci.plugins.docker.workflow.Docker$Image@7e65907b

My question is, why is DockerBuild.new() returning an object of type Docker$Image instead of docker_build.DockerBuild? Something weird is going on with the constructor and I am unable to even diagnose it. The output from any echo/println statements that I put in the constructor get lost except those that that get executed before the withRegistry() call. In fact, the output from image.pull() also gets lost. In another pipeline where I am doing a pull within the Jenkinsfile, I see output like this:

+ docker pull ...

Using default tag: latest

latest: Pulling from ...

Digest: sha256:f767e25c35c6977a336c080f16bd9c63fcdc04c405eb984d1c178e273d0547b8

Status: Image is up to date for ...

I am just following the Loading libraries dynamically section and I do want to get this working with dynamically loaded libraries as I want to avoid the global static configuration that is associated with the @Library annotations. I would appreciate any help in diagnosing or getting this working.

[Hari Krishna Dara]

By enclosing the body of the closure that is being executed in the constructor in a try/catch I noticed that there is an exception of type com.cloudbees.groovy.cps.impl.CpsCallableInvocation getting thrown. For some strange reason, new() wasn't propagating this exception and instead was returning the last evaluated value.