Common Expression Language Custom Task

[jerop]

Feature request

Add a CelRun Custom Task to provide CEL support in Pipelines. This allows us to experiment with CEL in Pipelines without adding CEL directly to the Tekton API surface. CelRun Custom Task is discussed in further detail as an alternative in Conditions Beta TEP.

Use cases

• guarded execution
  • feature request for expression language in guards
• string manipulation for parameters and other variables
• parsing yaml and referencing the data to enable parsing aspects of Pipeline behavior in a yaml

Related Issues:

• Feature: expression support in $()  #2812
• Feature: method to absorb git-source yaml into Pipeline/Task $inputs etc #2219
• Simple if/conditional support for skipping #2127
• Consider removing type from params (or _really_ support types) #1393

/cc @bobcatfish @bitsofinfo

[imjasonh]

FWIW when I was prototyping Custom Tasks I made https://github.com/imjasonh/cel-task to help demonstrate a simple CEL Task. It'll need some work to make sure it still works, and to add tests especially, but it might be a useful starting point.

[tekton-robot]

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[jerop]

/lifecycle frozen

because supporting CEL through a custom task is important for experimenting with the expression language without adding it to Tekton API surface -- expression language support is still highly requested (#2812)

[chitrangpatel]

Example that shows a usecase for CEL

In our plumbing repo we have a pipeline that computes go coverage, I was forced to write an additional task that split a string into two results so that I could use them as parameters into my next task that used a clone.

The ability to split the main param into two would have been incredibly useful (for e.g. something like https://tekton.dev/docs/triggers/cel_expressions/).