Andrew Bayer I am receiving the Label param from node as being required from jenkins/blue/rest/pipeline-metadata/agentMetadata?depth=20

After talking to Vivek Pandey he said I should ping you about it.

This is the full JSON response:
https://gist.github.com/NicuPascu/9ed1d96d4604274683ad2ef48a0778fc

I understand your reasoning but in the front-end a required field means it should not be empty e.g. "". I suggest we either leave things as they are now or if we want an empty string to be a valid value in BO then I suggest we change the isRequired to false. Vivek Pandey what do you think?

Yeah, I'm fine with leaving things as they are now. We're stuck with the required field bit for various historic reasons, but I don't think it's worth anyone's time to hack out a way to support empty string in the editor in this context when agent any achieves exactly the same thing.

I strongly disagree.  

"agent { label '' }" is valid declarative syntax.  If I open a pipeline with that syntax in it, Blue Ocean will report an error and force me not to use that syntax. That is not acceptable.

I understand that we'd like people to use "agent any" instead, but we should not be reporting an error in the editor for valid Declarative syntax.  

It sounds like this might be exposing a design bug - there plenty of situations where required string is allowed to be empty.  Is there no way to specify "required but may be an empty string"? 

Aaaaah - yes, that error is bad. Didn't think of that. There is no way to do "required but can be empty (or null)". Probably the best bet would be to have the conversion to JSON just shrug and change to agent any when it hits that scenario.

That sounds like a reasonable workaround to me.  

FYI, I've put up https://github.com/jenkinsci/pipeline-model-definition-plugin/pull/264 on the Declarative side - this'll convert

agent {
  label ''
}

to the JSON for agent any when translating to JSON for the editor, which will unbreak the most general use case for an empty string label. However, it'll still have an empty string label in the JSON if there are additional options, like in the case of

agent {
  label ''
  customWorkspace '/some/path'
}

...so even with this, the editor should still ideally have a way to specify an empty string for the label.

Nicolae Pascu, I think that the approach that Liam Newman and Andrew Bayer support makes sense. In that case, I don't think we need any editor changes. Is that correct?

Andrew Bayer, with your change, do we need to do any updates to the frontend editor?

I don’t believe so, no.

Awesome, thanks Andrew Bayer, I will close this issue then.

Code changed in jenkins
User: Andrew Bayer
Path:
pipeline-model-api/src/main/java/org/jenkinsci/plugins/pipeline/modeldefinition/ast/ModelASTAgent.java
pipeline-model-definition/src/test/java/org/jenkinsci/plugins/pipeline/modeldefinition/parser/ModelParserTest.java
pipeline-model-definition/src/test/resources/agentLabelEmptyString.groovy
http://jenkins-ci.org/commit/pipeline-model-definition-plugin/c18ba8695ff32a4cb81e711aaed5ee8a5718021e
Log:
JENKINS-43016 Convert empty string label agent to agent any in JSON

This'll make the editor happier - the label agent type does require an
argument, but an empty string is a valid (but weird) use case. The
editor, however, has no way of distinguishing between "you didn't
specify a label" and "you specified an empty string for the
label". There still should be work in the editor to figure out how to
actually handle this situation, but this fix at least will unbreak
existing Jenkinsfiles with empty string label agents being opened in
the editor, by converting the JSON in that case to be `agent any`,
which is functionally equivalent if no additional options are specified.

However, if additional options are specified (such as
`customWorkspace`), we have to punt and keep using the empty string
label agent.

Code changed in jenkins
User: Andrew Bayer
Path:
pipeline-model-api/src/main/java/org/jenkinsci/plugins/pipeline/modeldefinition/ast/ModelASTAgent.java
pipeline-model-definition/src/test/java/org/jenkinsci/plugins/pipeline/modeldefinition/parser/ModelParserTest.java
pipeline-model-definition/src/test/resources/agentLabelEmptyString.groovy
http://jenkins-ci.org/commit/pipeline-model-definition-plugin/c3dc1ea6badcabe2c3c383c561e1e986ea30e0e2
Log:
Merge pull request #264 from abayer/jenkins-43016

JENKINS-43016 Convert empty string label agent to agent any in JSON

Compare: https://github.com/jenkinsci/pipeline-model-definition-plugin/compare/3b74fc799c00...c3dc1ea6badc
*NOTE:* This service been marked for deprecation: https://developer.github.com/changes/2018-04-25-github-services-deprecation/

Functionality will be removed from GitHub.com on January 31st, 2019.