Forward Flow PR not opening after changes made directly in the VMR

[dkurepa]

Pull request

no PR got opened

Type of problem

Codeflow PRs not getting created

Description of the issue

If the following scenario happens, the service is unable to open up Forward Flow PRs:

• A change is made directly in the VMR, touching file Foo in repo A
• A number forward flows come from repo A but they're not touching the file FOO
• Finally, Foo is changed in the repo A, and we try to open a FF PR.
• This fails because there's a conflict in file Foo, so we recreate the last FF and try to apply the diff again, but it fails again, because the last FF isn't old enough

Essentially, we need to go a lot more back in these scenarios, to the last FF before file Foo was manually changed

[premun]

Next steps: write a test and have a chat about what actually happens

[dkurepa]

here's the test that shows what's wrong here https://github.com/dkurepa/arcade-services/blob/c79e186276eb7a3f517b358f80bdf710fb2cfc98/test/Microsoft.DotNet.DarcLib.Codeflow.Tests/VmrTwoWayCodeflowTest.cs#L867C5-L867C29

[premun]

Seems like the code in forward flower:

        // Reconstruct the previous flow's branch
        await FlowCodeAsync(
            lastLastFlows,
            lastFlow,
            sourceRepo,
            mapping,
            previouslyAppliedBuild,
            excludedAssets,
            targetBranch,
            headBranch,
            headBranchExisted,
            cancellationToken);

        // We apply the current changes on top again - they should apply now
        try
        {
            return await _vmrUpdater.UpdateRepository(
                mapping,
                build,
                resetToRemoteWhenCloningRepo: ShouldResetClones,
                cancellationToken: cancellationToken);
        }
        catch (Exception e)
        {
            _logger.LogCritical("Failed to apply changes on top of previously recreated code flow: {message}", e.Message);
            throw;
        }

should rather be something like this:

FlowCode(int recreateDepth) {
  try {
      FlowCurrentCode();
  } catch {
      RecreateFlows(recreateDepth);
      try {
        FlowCurrentCode();
      } catch {
        FlowCode(recreateDepth + 1);
      }
  }
}

so that it's recursively trying to recreate all of the previous flows.