Convert YAML to ModelASTPipelineDef

example.groovy

import org.jenkinsci.plugins.pipeline.modeldefinition.parser.Converter
import org.jenkinsci.plugins.pipeline.modeldefinition.parser.JSONParser
import net.sf.json.JSONObject
import org.yaml.snakeyaml.Yaml
import com.github.fge.jsonschema.tree.JsonTree
import org.jenkinsci.plugins.pipeline.modeldefinition.ast.ModelASTPipelineDef

String yamlString = """
pipeline:
  stages:
  - name: foo
    stages:
    - name: bar
      branches:
      - name: default
        steps:
        - name: echo
          arguments:
          - key: message
            value:
              isLiteral: false
              value: '"In stage \${STAGE_NAME} in group foo"'
    - name: baz
      branches:
      - name: default
        steps:
        - name: echo
          arguments:
          - key: message
            value:
              isLiteral: false
              value: '"In stage \${STAGE_NAME} in group foo"'
  agent:
    type: none
"""

Yaml yaml = new Yaml()
Map<String,Object> parsed = (Map<String, Object>) yaml.load(yamlString)
JSONObject jsonObject = new JSONObject(parsed);
JsonTree tree = Converter.jsonTreeFromJSONObject(jsonObject)
JSONParser parser = new JSONParser(tree)
ModelASTPipelineDef pipeline = parser.parse()
println pipeline