Merging stacked PRs
Aviator offers an open-source CLI for managing stacked PRs within GitHub. When used alongside Aviator MergeQueue, it simplifies the process of validating and merging those stacked PRs (or subset of those stacked PRs) together.
When requested to merge stacked PRs, Aviator will validate all the stacked PRs as if they were a single PR, and then merge them together after validation. The merge behavior may be slightly different depending on the queue mode.
Queueing action
To merge a subset of the stack, request a merge for the topmost PR in that subset. So for instance, if your stack is:
Requesting a stack-merge action for PR#3 will validate PR#1, PR#2 and PR#3 leaving PR#4 untouched. After merging, the stack would look like:
There are a few ways to request queueing a stack of PRs.
Chrome Extension (recommended): This is the simplest way to request way since the user experience for this is very similar to merging a regular PR. Go to
PR#3from above example in GitHub and click "Queue pull request" button:
CLI: Another way to queue the PR is via the
avcommand line. Simply checkout the branch associated withPR#3and run the command:
Note that, using this command requires authenticating the CLI with your Aviator account.
Slash command: A stack or sub-stack can also be merged by commenting a slash command from the GitHub interface:
Note that the slash command /aviator merge does not work to merge stacked PRs.
Merge behavior
Depending on the queue mode being used, the merge behavior for stacked PRs can vary.
Sequential mode (default mode)
Taking the example above, in sequential mode:
Aviator will consider
PR#1,PR#2andPR#3as a single PR in the queue.When this PR reaches the top of the queue, Aviator only updates
PR#3with the target branch (mainline), and run the CI.Once the CI passes, Aviator will change the base branch of
PR#3and merge itSince
PR#3is stacked on top ofPR#1andPR#2, merging PR#3 also merges all the changes associated withPR#1andPR#2.Since GitHub does not recognize that
PR#1andPR#2are already merged, Aviator automatically closes them and applies the GitHub labelmerged-by-mqto represent that the PRs are indeed merged.
See also Separating the merge commits.
Parallel mode
Similar to Sequential mode, parallel mode also considers the stack as a single PR in the queue. In parallel mode:
Aviator creates a batch using the head branch of
PR#3including all the changes ofPR#1andPR#2as well.After the batch passes CI, Aviator changes the base branch of
PR#3and merges it.Since
PR#3is stacked on top ofPR#1andPR#2, merging PR#3 also merges all the changes associated withPR#1andPR#2.As in Sequential mode, Aviator closes
PR#1andPR#2, while applying the GitHub labelmerged-by-mqto represent that the PRs are indeed merged.
See also Separating the merge commits.
Fast forwarding
Fast forwarding mode provides a simpler experience for merging stacked PRs. Since in case of fast-forwarding, we fast-forward the mainline to commits in draft PRs, the CI is already passing. This allows Aviator to merge the PRs individually without GitHub blocking the commits.
In fast-forwarding mode:
When the stack with
PR#3is requested merging, Aviator creates one squash commit for each PR in the stack.After CI passes, the mainline is fast-forwarded to the latest commit in the batch associated with
PR#3, this includes separate commits associated withPR#2andPR#1in the linear history.
Separating the merge commits
By default the Sequential and Parallel modes create a single commit in the mainline for all of the stacked PRs that are queued together. This is because GitHub does not let an app account bypass the branch protection rules. Even when allowed to bypass the rules, GitHub will let the Aviator app only bypass the approval requirement and PR creation requirement, not the CI validation requirement.
Rulesets
This capability of bypassing the CI requirement is now available using GitHub’s Rulesets. Rulesets offer feature parity with the configurations you use in classic branch protection rules and you should be able to migrate all your existing configurations to using Rulesets.
Once migrated to Ruleset, you can add Aviator app in the bypass list.
Configuring separate commits
Once Rulesets are configured and other GitHub branch protection rules are disabled, you can configure Aviator to start creating separate commits for stacked PRs. To do so, set the following in the merge_strategy section of the configuration YAML.
For details, refer to the configuration reference.
If you need assistance in setting up the Rulesets, please contact howto@aviator.co.
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