Added support to pass values to sub-charts via map.yaml

[jorgecarleitao]

What this PR does / why we need it:

This PR allows developers to declare a map.yaml file on their chart, which can be used to map values in values.yaml to derived values that are used in templating, including sub-charts (see #8576 for the long explanation). This allows developers to write e.g.

apiVersion: v1
description: Chart with map and subcharts
name: chart-with-map
version: 0.0.1
dependencies:
  - name: backend
    version: 0.0.1
  - name: frontend
    version: 0.0.1

# values.yaml
domain: example.com

# map.yaml
backend:
  uri: {{ printf "https://api.%s" .Values.domain }}

frontend:
  uri: {{ printf "https://app.%s" .Values.domain }}

other_uri: {{ printf "https://blabla.%s" .Values.domain }}

thereby not having to expose backend: uri, frontend: uri in values.yaml (for the subchart), nor ask chart users to have to pass the same value in multiple keys for consistency (or use global names that lead to naming collisions).

I.e. it allows subcharts to be populated with derived (or maped) values without exposing these values to values.yaml (the public interface of the chart).

This solves a long standing issue of being very painful to pass values to subcharts that derive values in values.yaml (more details in #8576). Closes #8576.

Special notes for your reviewer: This PR is not complete yet: this is part of the proposal, and is intended to demonstrate how the proposal is implemented in practice. There are at least three issues to address, two documented as # todo, plus associated documentation.

To run the example,

make build
./bin/helm install test --debug --dry-run cmd/helm/testdata/testcharts/chart-with-map/

which leads to the manifest

---
# Source: chart-with-map/charts/subchart/templates/test1.yaml
apiVersion: v1
kind: Pod
metadata:
    name: "aaa"
    labels:
        derived: aa-a
        default: aa
---
# Source: chart-with-map/templates/test1.yaml
apiVersion: v1
kind: Pod
metadata:
    name: "aaa"
    labels:
        derived: a-a
        public1: a

If applicable:

• this PR contains documentation
• this PR contains unit tests
• this PR has been tested for backwards compatibility

[TBBle]

As a note, by doing this work in recAllTpls, import-values won't be able to see the data from map.yaml as chartutil.ProcessDependencies calls processImportValues much earlier in the flow.

[bacongobbler]

Hi @jorgecarleitao. We're asking new proposals to first write up a Helm Improvement Proposal, also known as a HIP. This gives the maintainers an opportunity to consider the design of the proposal and iron out any design kinks before a reference implementation is provided. This saves both you and us time in the long run.

Please have a read through https://github.com/helm/community/blob/master/hips/hip-0001.md and let me know if you have any questions.

[m-yosefpor]

any progress on this?

[bacongobbler]

No further progress has been made since chnages were requested 12 months ago. Closing as stale.

[agates4]

@jorgecarleitao please don't give up. :)

[treksler]

Expecting anyone who is capable and willing to write code (for free) to write an HIP document instead is nuts. Like 100% nuts. If you have a problem where people are writing code that seems like it is coming out of left field, then you have lost touch with your user base, not the other way around.