[Bug]: instanceof for library classes is false in template and other steps

[steven-terrana]

Jenkins Version

LTS

JTE Version

2.3

Bug Description

Instantiations of library provided classes are not recognized outside of the step where they were created.

Root Cause

After some digging I've identified the root cause of this problem.
The Pipeline Template, and each StepWrapperScript, are compiled with different classloaders.

Pipeline execution begins via CpsFlowExecution.start(). During start(), the Pipeline Template is compiled by a CpsGroovyShell created by a CpsGroovyShellFactory within CpsFlowExecution.parseScript() which results in the normal classloader that's typically used in a Jenkins pipeline. See workflow-cps/doc/classloader.md for more info there.

Each JTE library step is compiled by creating individual mock CpsFlowExecution and running parseScript(), which follows the same process as above to create the StepWrapperScript - resulting in each step having its own classloader. This happens within StepWrapperFactory.prepareScript().

So far, attempts at creating a common classloader shared by the Pipeline Template and each StepWrapperScript have failed - resulting in either compilation errors or serialization errors preventing rehydrating after a restart.

The compilation errors are coming from the fact that the template and steps require a different CompilerConfiguration which we modify in various GroovyShellDecorator extensions (PipelineTemplateCompiler and StepWrapperShellDecorator) and that CompilerConfiguration is actually stored on the GroovyClassLoader.

Steps to Reproduce

create a library with a class:

class Build implements serializable{}

create a step to instantiate a Build object:

// createBuild.groovy
import Build
Build call(){
  return new Build()
}

create another step to check instanceof:

// checkBuild.groovy
import Build
void call(def b){
  println b instanceof Build // should be true, but is false
}

pipeline template:

def b = createBuild()
checkBuild(b)