SparseCheckout in Jenkinsfile pipeline - jenkins

Question

In a jenkinsfile, I have specified the folderName through SparseCheckoutPaths which I want to checkout. But I am getting a whole branch checkout instead.
checkout([$class: 'GitSCM',
branches: [[name: '*/branchName']],
extensions: [[$class: 'SparseCheckoutPaths', path: 'FolderName']],
userRemoteConfigs: [[credentialsId: 'someID',
url: 'git#link.git']]])

Answer 1

Here comes the answer to my own question. For a bit of background how does it work, there is flag/configuration for git client called sparsecheckout which is responsible for this kind of checkout. Additionally, a sparse-checkout named file is also required. For more info look here.
My problem was the syntax for the Jenkinsfile and correct one is as follows:
checkout([$class: 'GitSCM',
branches: [[name: '*/branchName']],
doGenerateSubmoduleConfigurations: false,
extensions: [
[$class: 'SparseCheckoutPaths', sparseCheckoutPaths:[[$class:'SparseCheckoutPath', path:'folderName/']]]
],
submoduleCfg: [],
userRemoteConfigs: [[credentialsId: 'someID',
url: 'git#link.git']]])
for more info, here comes the github-link

Answer 2

You can define a custom step sparseCheckout in a shared library that adds on top of the existing checkout scm.
vars/sparseCheckout.groovy:
def call(scm, files) {
if (scm.class.simpleName == 'GitSCM') {
def filesAsPaths = files.collect {
[path: it]
}
return checkout([$class : 'GitSCM',
branches : scm.branches,
doGenerateSubmoduleConfigurations: scm.doGenerateSubmoduleConfigurations,
extensions : scm.extensions +
[[$class: 'SparseCheckoutPaths', sparseCheckoutPaths: filesAsPaths]],
submoduleCfg : scm.submoduleCfg,
userRemoteConfigs : scm.userRemoteConfigs
])
} else {
// fallback to checkout everything by default
return checkout(scm)
}
}
Then you call it with:
sparseCheckout(scm, ['path/to/file.xml', 'path2])

Answer 3

Your syntax looks good, but, as seen in "jenkinsci/plugins/gitclient/CliGitAPIImpl.java", did you specify the right configuration?
private void sparseCheckout(#NonNull List<String> paths) throws GitException, InterruptedException {
boolean coreSparseCheckoutConfigEnable;
try {
coreSparseCheckoutConfigEnable = launchCommand("config", "core.sparsecheckout").contains("true");
} catch (GitException ge) {
coreSparseCheckoutConfigEnable = false;
}
In other words, is git config core.sparsecheckout equal to true in the repo you are about to checkout?