Azure DevOps multi-repo, multi-branch-trigger, selecting the branch to build from - azure-devops

Question

In an Azure DevOps pipeline, I had
resources:
repositories:
- repository: self
type: git
name: MyProject.Web
trigger:
- master
- repository: UiRepo
type: git
name: MyProject.Web.UI
trigger:
- main
[other stuff]
steps:
- checkout: self
- checkout: UiRepo
[other stuff]
This has worked fine: The pipeline ran when triggered by completion of a pull request to either the master branch of the "self" repo or the main branch of the UiRepo. The checkouts pulled from the master branch of "self" and the main branch of UiRepo.
Now I'm adding a branch called release/1.0 to each of the repos, and will introduce other release/x.x branches in the future. So now I have:
resources:
repositories:
- repository: self
type: git
name: MyProject.Web
trigger:
- master
- release/*
- repository: UiRepo
type: git
name: MyProject.Web.UI
trigger:
- main
- release/*
[other stuff]
steps: # ??????
- checkout: self
- checkout: UiRepo
[other stuff]
Now the following is required:
If the triggering branch's name ($Build.SourceBranchName) is either 'master' or 'main', check out master from "self" and main from UiRepo.
Otherwise, check out a branch whose value is $Build.SourceBranch from both repos.
At https://learn.microsoft.com/en-us/azure/devops/pipelines/repos/multi-repo-checkout?view=azure-devops#checking-out-a-specific-ref, I've read that I can use inline syntax in the checkout steps to include specific refs. In my case, I think this comes out as follows:
- ${{ if in(variables['Build.SourceBranchName''], 'master', 'main') }}:
- checkout: git://MyProject/MyProject.Web#refs/heads/master
- checkout: git://MyProject/MyProject.Web.UI#refs/heads/main
- ${{ else }}
- checkout: git://MyProject/MyProject.Web#$(Build.SourceBranch)
- checkout: git://MyProject/MyProject.Web.UI#$(Build.SourceBranch)
(or do I need to be using [ variables['Build.SourceBranch'] ] here instead of $(Build.SourceBranch)?)
But, by dispensing with the references in the checkout steps to "self" and UiRepo, this seems to be divorcing the connection between the checkout steps and the repos as I've already defined them. Does that matter? Is this correct anyway? If it isn't, how can I accomplish my goal?

Answer 1

The if/else you are using is named Conditional Insertion in DevOps concept.
Need to clarify is in this concept, it indeed can accept predefined variables， but only which is 'Available in templates'.
I notice you are using Build.Repository.SourceBranchName, this variable not even in the list of predefined variables, let alone the concept of 'Available in templates'. So the first part of your Conditional Insertion will not be process. Only the second part will be able to process.
And please do not use 'self' as the alias of the repository, this will causes ambiguity.(Your current situation use this is no problem, this is just a suggestion.)
So basically, your pipeline definition should be like this:
trigger:
- none
resources:
repositories:
- repository: self
type: git
name: Repo1
trigger:
- master
- release/*
- repository: UiRepo
type: git
name: Repo2
trigger:
- main
- release/*
pool:
vmImage: ubuntu-latest
steps:
- ${{ if in(variables['Build.SourceBranchName'], 'master', 'main') }}: #This place needs to change
- checkout: git://BowmanCP/Repo1#refs/heads/master
- checkout: git://BowmanCP/Repo2#refs/heads/main
- ${{ else }}:
- checkout: git://BowmanCP/Repo1#$(Build.SourceBranch)
- checkout: git://BowmanCP/Repo2#$(Build.SourceBranch)
Works prefect on my side: