Allow Starlark source to be defined in Kptfile

[FrenchBen]

Describe your problem

functionConfig currently supports 2 approaches:

• Run via Kptfile
• Run via CLI arguments

While these 2 approaches provide some flexibility in testing, it also creates inequality for certain functions, more specifically Starlark.

Example

Taking the core example of Starlark Configmap

# fn-set-replicas.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: set-replicas
data:
  replicas: "5"
  source: |
    def setReplicas(resources, replicas):
      for r in resources:
        if r["apiVersion"] == "apps/v1" and r["kind"] == "Deployment":
          r["spec"]["replicas"] = replicas
    replicas = ctx.resource_list["functionConfig"]["data"]["replicas"]
    setReplicas(ctx.resource_list["items"], replicas)

When running this, a few options are available:

1. Call it via config map: kpt fn eval --image gcr.io/kpt-fn/starlark:v0.3 --fn-config fn-set-replicas.yaml
2. Add it to your Kptfile, and call kpt fn render

apiVersion: kpt.dev/v1
kind: Kptfile
metadata:
  name: sample-pkg
info:
  description: sample description
pipeline:
  mutators:
    - image: gcr.io/kpt-fn/starlark:v0.3
      configPath: fn-set-replicas.yaml

But a 3rd option exists, which is to extract the Starlark code into a much more user-friendly (and editor parsable) file:

#set-replicas.star
    def setReplicas(resources, replicas):
      for r in resources:
        if r["apiVersion"] == "apps/v1" and r["kind"] == "Deployment":
          r["spec"]["replicas"] = replicas
    replicas = ctx.resource_list["functionConfig"]["data"]["replicas"]
    setReplicas(ctx.resource_list["items"], replicas)

Then run it via:
kpt fn eval --image gcr.io/kpt-fn/starlark:v0.3 -- source="$(cat set-replicas.star)" replicas=5

The problem is that you cannot then bring this back into your Kptfile, forcing you to copy this back into your awkward yaml file.

Solution

Add support for Starlark file parsing, from a Kptfile. Similar to the configPath or configMap option, add a sourcePath option where a .star file path could be declared.

apiVersion: kpt.dev/v1
kind: Kptfile
metadata:
  name: sample-pkg
info:
  description: sample description
pipeline:
  mutators:
    - image: gcr.io/kpt-fn/starlark:v0.3
      sourcePath: set-replicas.star
      configMap:
          replicas: 5

Which would result in something like:

# set-replicas.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: set-replicas
data:
  replicas: "5"
  source: | <insert-content-from-sourcePath>

[droot]

Another solution that has been discussed: include-file support

[FrenchBen]

Closing as duplicate of #2350