In a freestyle build I suppose this would simply set build variables.

Or via EnvironmentContributingAction, which is also not an option for a SimpleBuildStep due to JENKINS-29537.

Without JENKINS-40070, Run.getEnvironment cannot be used as a workaround.

Has there been any progress on this issue? This is blocking our company from updating our jobs to from Freestyle to Pipelines.

Could the solution be as easy as doing what the old

AbstractBuild getEnvironment()

did which was holding onto an array that contained the RunListener's environments and NodeProperty's environments? And then in

Run getEnvironment()

we could add the environments from the array we gathered via 

buildEnvironmentFor(this,env,listener);

?

This is blocking our company from …

If you implement Step directly there are no restrictions.

Could the solution be as easy as …

No, that is not how it would work.

Jesse Glick The header of our class is

public class IntrepidBuilder extends Builder implements SimpleBuildStep

since we want our plugin to be compatible with both Freestyle and Pipelines. How might we update this to still allow the end user to use the "pipeline syntax generator" to call our build step?

Currently if you want to access environment variables, you cannot; you must implement Step instead.

How come the CHANGE_URL env variable is defined in multi-branch pipeline jobs (PRs) and this is accessible by adding to a publish/post step

public boolean prepare(final Run<?, ?> run) {
Map<String, String> env = null;
try {
    env = getEnvironment(run, new LogTaskListener(LOGGER, Level.INFO));
    env.forEach((k, v) -> log("key: " + k + " value:" + v)); 
    .
    .
    .

but GIT_URL and GIT_BRANCH is not?

I'm trying to push from the warnings post step to the PR in Github. So far I can do it from a freestyle job and a PR in a multi branch pipeline but not in a standard pipeline, mainly because I can't derive the github url or github branch

Jeremy Marshall CHANGE_URL is defined in branch-api. GIT_URL etc. are map keys in the return value of git / checkout, done in JENKINS-26100.