Crossplane Composition Functions IO

fnio.yaml

apiVersion: apiextensions.crossplane.io/v1alpha1
kind: FunctionIO
# Optional arbitrary KRM-like resource. Each function in a pipeline will be
# called with its own function config (i.e. config is not pipelined).
config:
  apiVersion: database.example.org/v1alpha1
  kind: Config
  metadata:
    name: cloudsql
  spec:
    version: POSTGRES_9_6
# The composite resource (including metadata, spec, and status)
composite:
  apiVersion: database.example.org/v1alpha1
  kind: XPostgreSQLInstance
  metadata:
    name: my-db
  spec:
    parameters:
      storageGB: 20
    compositionSelector:
      matchLabels:
        provider: gcp
    writeConnectionSecretToRef:
      name: db-conn
# TODO(negz): What if we just took the resources array of a Composition,
# including patches etc? Is there value in that? Code could just ignore patches
# and return fully formed bases if it wanted to. I like that this would make
# the data structure identical to a Composition resources array, but is there
# any other value? Would it be limiting to try to keep them identical? (Probably yes.)
resources:
- name: cloudsqlinstance
  base:
    apiVersion: database.gcp.crossplane.io/v1beta1
    kind: CloudSQLInstance
    metadata:
      name: cloudsqlpostgresql
    spec:
      forProvider:
        databaseVersion: POSTGRES_9_6
        region: us-central1
        settings:
          tier: db-custom-1-3840
          dataDiskType: PD_SSD
          dataDiskSizeGb: 20
      writeConnectionSecretToRef:
        namespace: crossplane-system
        name: cloudsqlpostgresql-conn
  connectionDetails:
  - name: hostname
    fromConnectionSecretKey: hostname
  # TODO(negz): Do we want readiness checks too? Should the function be able to
  # write to the status of the XR directly to set a status?
results:
- severity: Error
  message: "Could not render Database.postgresql.crossplane.io/v1alpha1`

@turkenh I ended up pushing a commit to crossplane/crossplane#2886 that adopts a stripped down version of the FunctionIO API. I'd like to roll this conversation into that PR - I'll respond to your latest comment there. Thanks!