TEP-0056: Pipelines in Pipelines. Matrix fan-out of PipelineRef.

[twoGiants]

Feature request

Support fanning out PipelineTasks with Pipelines into multiple child PipelineRuns using Matrix. Currently, Matrix only supports fanning out Tasks into TaskRuns and Custom Tasks into CustomRuns.

This includes:

• Fan out a PipelineTask using pipelineRef or pipelineSpec into multiple child PipelineRuns based on Matrix parameter combinations
• Aggregate status from all fanned-out child PipelineRuns
• Update docs/pipelines-in-pipelines.md known limitations section and documentation

See TEP-0056: Matrix.

Use case

A compliance Pipeline needs to run against multiple repositories in an organization. The repositories are passed as a Matrix parameter:

tasks:
  - name: compliance-scans
    matrix:
      params:
        - name: repo
          value:
            - https://github.com/tektoncd/pipeline
            - https://github.com/tektoncd/triggers
            - https://github.com/tektoncd/results
    pipelineRef:
      name: compliance-pipeline

See also TEP-0056: Fanning Out Pipelines.