Overlaying a configmap that's fully populated

apply-custom-values.yaml

#@ load("@ytt:overlay", "overlay")
#@ load("@ytt:data", "data")

#@ def tekton_pipeline_configmap():
apiVersion: v1
kind: ConfigMap
metadata:
  name: feature-flags
  namespace: tekton-pipelines
#@ end

#@ def custom_config():
#@overlay/match-child-defaults missing_ok=True
data: #@ data.values["tekton-config"]
#@ end

#@overlay/match by=overlay.subset(tekton_pipeline_configmap())
#@overlay/replace via=lambda upstream, _: overlay.apply(upstream, custom_config())
---

custom-values.yaml

#@data/values
---
tekton-config:
  disable-creds-init: "true"

schema.yaml

#@data/values-schema
---
tekton-config:
  #@schema/validation one_of=["true", "false"]
  disable-affinity-assistant: "false"
  #@schema/validation one_of=["true", "false"]
  disable-creds-init: "false"
  #@schema/validation one_of=["true", "false"]
  await-sidecar-readiness: "true"
  #@schema/validation one_of=["true", "false"]
  running-in-environment-with-injected-sidecars: "true"
  #@schema/validation one_of=["true", "false"]
  require-git-ssh-secret-known-hosts: "false"
  #@schema/validation one_of=["true", "false"]
  enable-tekton-oci-bundles: "false"
  #@schema/validation one_of=["stable", "beta", "alpha"]
  enable-api-fields: "stable"
  #@schema/validation one_of=["true", "false"]
  send-cloudevents-for-runs: "false"
  #@schema/validation one_of=["enforce", "skip", "warn"]
  resource-verification-mode: "skip"
  #@schema/validation one_of=["true", "false"]
  enable-provenance-in-status: "false"
  #@schema/validation one_of=["v1alpha1", "v1beta1"]
  custom-task-version: "v1beta1"
  #@schema/validation one_of=["none", "spire"]
  enforce-nonfalsifiablity: "none"

tekton-feature-flags-configmap.yaml

# Copyright 2019 The Tekton Authors
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

apiVersion: v1
kind: ConfigMap
metadata:
  name: feature-flags
  namespace: tekton-pipelines
  labels:
    app.kubernetes.io/instance: default
    app.kubernetes.io/part-of: tekton-pipelines
data:
  # Setting this flag to "true" will prevent Tekton to create an
  # Affinity Assistant for every TaskRun sharing a PVC workspace
  #
  # The default behaviour is for Tekton to create Affinity Assistants
  #
  # See more in the workspace documentation about Affinity Assistant
  # https://github.com/tektoncd/pipeline/blob/main/docs/workspaces.md#affinity-assistant-and-specifying-workspace-order-in-a-pipeline
  # or https://github.com/tektoncd/pipeline/pull/2630 for more info.
  disable-affinity-assistant: "false"
  # Setting this flag to "true" will prevent Tekton scanning attached
  # service accounts and injecting any credentials it finds into your
  # Steps.
  #
  # The default behaviour currently is for Tekton to search service
  # accounts for secrets matching a specified format and automatically
  # mount those into your Steps.
  #
  # Note: setting this to "true" will prevent PipelineResources from
  # working.
  #
  # See https://github.com/tektoncd/pipeline/issues/2791 for more
  # info.
  disable-creds-init: "false"
  # Setting this flag to "false" will stop Tekton from waiting for a
  # TaskRun's sidecar containers to be running before starting the first
  # step. This will allow Tasks to be run in environments that don't
  # support the DownwardAPI volume type, but may lead to unintended
  # behaviour if sidecars are used.
  #
  # See https://github.com/tektoncd/pipeline/issues/4937 for more info.
  await-sidecar-readiness: "true"
  # This option should be set to false when Pipelines is running in a
  # cluster that does not use injected sidecars such as Istio. Setting
  # it to false should decrease the time it takes for a TaskRun to start
  # running. For clusters that use injected sidecars, setting this
  # option to false can lead to unexpected behavior.
  #
  # See https://github.com/tektoncd/pipeline/issues/2080 for more info.
  running-in-environment-with-injected-sidecars: "true"
  # Setting this flag to "true" will require that any Git SSH Secret
  # offered to Tekton must have known_hosts included.
  #
  # See https://github.com/tektoncd/pipeline/issues/2981 for more
  # info.
  require-git-ssh-secret-known-hosts: "false"
  # Setting this flag to "true" enables the use of Tekton OCI bundle.
  # This is an experimental feature and thus should still be considered
  # an alpha feature.
  enable-tekton-oci-bundles: "false"
  # Setting this flag will determine which gated features are enabled.
  # Acceptable values are "stable", "beta", or "alpha".
  enable-api-fields: "stable"
  # Setting this flag to "true" enables CloudEvents for CustomRuns and Runs, as long as a
  # CloudEvents sink is configured in the config-defaults config map
  send-cloudevents-for-runs: "false"
  # Setting this flag to "enforce" will enforce verification of tasks/pipeline. Failing to verify
  # will fail the taskrun/pipelinerun. "warn" will only log the err message and "skip"
  # will skip the whole verification
  resource-verification-mode: "skip"
  # Setting this flag to "true" enables populating the "provenance" field in TaskRun
  # and PipelineRun status. This field contains metadata about resources used
  # in the TaskRun/PipelineRun such as the source from where a remote Task/Pipeline
  # definition was fetched.
  enable-provenance-in-status: "false"
  # Setting this flag will determine the version for custom tasks created by PipelineRuns.
  # Acceptable values are "v1beta1" and "v1alpha1".
  # The default is "v1beta1".
  custom-task-version: "v1beta1"
  # Setting this flag will determine how Tekton pipelines will handle non-falsifiable provenance.
  # If set to "spire", then SPIRE will be used to ensure non-falsifiable provenance.
  # If set to "none", then Tekton will not have non-falsifiable provenance.
  # This is an experimental feature and thus should still be considered an alpha feature.
  enforce-nonfalsifiablity: "none"