Summary

I would propose to enhance the git generator to be able to fetch parameters from a file, in addition to the values directly provided as key/values

Motivation

Let's say I have two sources to templatize my Applications: a list of tenants with their configurations and a file containing the version of the application to deploy, and technical information not related to the tenants.

Today, if we want to provide values from different files to templatize an Application using an ApplicationSet, we need to create a matrix like so:

spec:
  generators:
    - matrix:
        generators:
          - git:
            repoUrl: http://myGitRepo
            revision: HEAD
            files:
              - path/to/tenants/*.yaml
            pathParamPrefix: "tenant"
          - git:
            repoUrl: http://myGitRepo
            revision: HEAD
            files:
            - path/to/appConfig/{{.tenant.version}}/appconfig.yaml

This complexifies the lisibility, especially if we multiply the number of file sources (ending up with matrix of matrix of...)

Proposal

I would propose to be able to provide extra parameters as files inside a git generator, to be applied on top of the parameters provided by the files.
This would avoid Cartesian product across generators.

spec:
  generators:
      - git:
        repoUrl: http://myGitRepo
        revision: HEAD
        files:
          - path/to/tenants/*.yaml
        pathParamPrefix: "tenant"
        extraParameterFiles:
        - path/to/another/someBaseConfig.yaml
        - path/to/appConfig/{{.tenant.version}}/appconfig.yaml

The extraParameterFiles would be merged by using a priority in the list, from bottom to top, like the helm values at Application level.
The limitation (I think acceptable) is that the files should be in the same git repo (and revision).