Change several branches in the same repo

Created by: malomarrec

User problem

Some customers use long-lived branches to define versions or releases. A use case for batch changes is to update each of those branches, for example bumping up dependency versions or changing boilerplate code.

Example repo: implements a function foo

dependent-repo has:

• branch: release1 imports repo and uses foo
• branch: release2 imports repo and uses foo
• branch: release3 imports repo and uses foo

Use case: foo gets deprecated, and needs to be replaced by foo2 in all releases in dependent-repo. Each branch is managed by a different team, so there needs to be one changeset per branch.

Current state

• This is not supported today.
• Batch Changes has most of the utilities to define such changes, including batch changes creating several branches and changeset in the same repo and templating to define unique branch names
• Batch Changes already supports changing a specific branch
• Batch Changes does not support changing multiple branches from the same repo

For example, this will only create a changeset on release-2:

name: multiple-branches
description: Creating changesets on multiple branches does not work

on:
  - repository: github.com/malomarrec/batch-change-testing-2
    branch: release-1
  - repository: github.com/malomarrec/batch-change-testing-2
    branch: release-2

steps:
  - run: touch hello-world.yml; cat release.yml
    container: alpine:3
    outputs:
      v:
          value: ${{step.stdout}}
          format: yaml


changesetTemplate:
  title: Multiple branches in the same repo
  body: Hello from the other siiiiiiiiiide
  branch: add-hw-${{outputs.v.release}}
  published: true
  commit:
    message: Hello, it's me.

Impacted customer

Feedback surfaced by: https://github.com/sourcegraph/accounts/issues/544

Proposal

Explicit repository: statements override repositoriesMatchingQuery. In the event multiple repository statements are defined with the same repo, only the last one is used. To support multiple branches, the branch: field can be a string or a list, and can also be named branches.

Examples

1. List out branches that I want to modify in a given repository

on:
  - repository: github.com/sourcegraph/automation-testing
    branches: [release-1, release-2]

Only returns the release-1, release-2 branches.

2. List out branches that I want to modify in a given repository, and mix and match with a query

on:
  - repositoriesMatchingQuery: file:README.md
  - repository: github.com/sourcegraph/automation-testing
    branches: [release-1, release-2]

If the query returns the main branch of sourcegraph/automation-testing, it is overridden by the set of branches named explicitly.

Out of scope

It would be great to modify all the branches in the list of repositories. It's out of scope for now, we might want to introduce a branchesMatchingQuery

on:
  - repositoriesMatchingQuery: repo:github\.com/sourcegraph/* rev:*refs/heads/dev* foo
  - repositoriesMatchingQuery: repo:github\.com/sourcegraph/* rev:*refs/heads/release-1* foo
  - repositoriesMatchingQuery: repo:github\.com/sourcegraph/* rev:*refs/heads/release-2*