Link to where the branch relationships are defined in automated merge PRs

[rainersigwald]

• This issue is blocking
• This issue is causing unreasonable pain

@dotnet-maestro-bot is sending nice PRs (like dotnet/msbuild#5806). They have a great link to the script that makes the PR (thanks!) but sometimes I'd like to know why a PR is happening. I remember that there's a repo somewhere with a bunch of data about the various repos and branches and relationships like "merge branch X into branch Y at cadence Z". But I don't usually remember exactly where that is.

Could it be linked in the PRs? Bonus points if the link goes directly to the line that cause the individual PR but just a static pointer to the file would be great.

[dagood]

You're looking for https://github.com/dotnet/versions/blob/master/Maestro/subscriptions.json, and yeah, should be easy enough to add the static URL.

Adding dynamic stuff gets more involved... would be a feature to add to https://github.com/dotnet/versions/tree/master/Maestro, working through it something like this:

1. Have the service figure out/store which lines of JSON defined the subscription.
2. Replace some token like <subscriptions-json-lines> with the value when it appears in a subscription.
   • <trigger-repo> works like this.
3. Handle the new arg in the GitHubMergeBranches.ps1.
4. Ask core-eng to deploy a new build of the Maestro service (not Maestro++).
5. Add the new "SubscriptionsJsonLines": "<subscriptions-json-lines>" arg mapping to each mirror subscription to link it all up.

[rainersigwald]

Yeah, the static URL should be fine. Doing it with detail sounds like more trouble than it's worth.