Automated Merge Up Action

This action creates a pull request to merge commits from one branch into another. It is designed to run on every push to keep branches for newer versions up-to-date.

Usage

A sample workflow is included in the examples directory. The workflow acts on every push to matching branches and uses this action to create a pull request up to the next branch.

The branch selection algorithm will target the branch for the next SemVer release with its pull request. For example, assuming a commit was pushed to v1.3, the branch selection will consider the following branches in order:

• v1.4
• v2.0
• The configured fallback branch (if set)

If no matching branch is found, the action exits without creating a pull request. The same applies when no mergeable commits are found. Once the merge-up pull request has been merged, the action will repeat the process until no matching branch has been found. It can thus be used to efficiently merge changes up through several releases, ensuring branch protection rules and CI requirements are met.

Dev branches

In addition to the branchNamePattern you can also specify a devBranchNamePattern input. This can be used if you are maintaining multiple major versions at the same time. Considering the default value for branchNamePattern (<major>.<minor>) and a devBranchNamePattern of <major>.x, the candidate branches when a commit is pushed to v1.3 looks like this:

• v1.4
• v1.x
• v2.0
• v2.x
• The configured fallback branch (if set)

When pushing to a branch that matches the dev name pattern (e.g. v1.x), only branches for the next major version are considered:

• v2.0
• v2.x
• The configured fallback branch (if set)

Default token

If you have no GitHub Actions workflows that are run when a new pull request is pushed, you can rely on the default token as long as you specify additional permissions for it:

permissions:
  contents: write
  pull-requests: write

If you need to run actions on newly created pull request, create a custom token with the repo scope and use it instead of the default github.token. Note that you also need to pass a token to the checkout action to ensure credentials are set in the Git repository to allow you to push a new branch.

Resolving Conflicts

The action creates an intermediate branch as head reference for the pull request. For example, when merging v1.3 into v1.4, the action will create a branch named merge-v1.3-into-v1.4-<token>. If there are conflicts in this merge, you can resolve these conflicts in this branch. There are two approaches for this:

Merge Base Branch

In the example above, you can merge v1.4 into this intermediate branch and resolve conflicts:

git merge --no-ff v1.4

After resolving conflicts, conclude the merge and push commits.

Starting fresh

If you would instead like to perform the merge manually, you can start out fresh. In the example above, this would look something like this:

git reset --hard v1.4
git merge --no-ff v1.3

After resolving commits, conclude the merge and push commits. This will require force-pushing since the commit history of the branches will diverge.

Configuration

The action supports the following input parameters:

ref (required)

The ref input identifies the reference being pushed. Typically, this will be ${{ github.ref_name }}

branchNamePattern (optional)

The branchNamePattern input can be used to configure the naming strategy for versioned branches. It defaults to <major>.<minor>. <major> and <minor> inside this pattern are used as placeholders and replaced accordingly. Note that the pattern needs to contain both placeholders for the action to function correctly. The branch name pattern is used for the following purposes:

• To check if the source ref name matches a versioned branch. For this purpose,
  the <major> and <minor> are replaced with [0-9]+ to perform a RegExp
  match
• To generate new branch names. When checking for branches, the placeholders are
  replaced with the computed values according to the SemVer release.

devBranchNamePattern (optional)

The devBranchNamePattern input can be used to configure the naming strategy for development (i.e. upcoming versions) branches. By default, it is empty and supports <major> as a placeholder. This pattern is used to match the branch name if it does not match the branchNamePattern, and is used to generate candidate branch names, where the <major> placeholder is replaced with the computed value according to the SemVer release.

fallbackBranch (optional)

If your branch naming pattern involves a non-versioned branch for the upcoming version (e.g. main), the fallbackBranch option can be used to specify this branch name. If no versioned branch was found, the pull request will target this fallback branch instead. The "Branch Selection" chapter above explains the order of operations.

enableAutoMerge (optional)

When this option is enabled (using a truish value), the resulting PR will have auto-merge enabled. Note that in order for this to work, the auto-merge functionality has to be enabled on the repository, and the "merge" merge strategy has to be available. Automatic merges are always done using the "merge" strategy.

Determine next branch

There is a separate action named get-next-branch that can be used to run the branch detection logic and return the determined information. This is useful if you want to run your own logic for handling merges.

- name: 'Determine branch to merge up to'
  id: get-next-branch
  uses: alcaeus/automatic-merge-up-action/get-next-branch@main
  with:
    ref: ${{ github.ref_name }}
    branchNamePattern: 'v<major>.<minor>'
    fallbackBranch: 'master'

The action takes the same inputs as the default create-pr action, except for the enableAutoMerge input which doesn't exist. The action sets two outputs:

• hasNextBranch: this bool output is true if the branch detection logic
  found a branch to merge up to, false otherwise.
• branchName: this is the name of the next branch in the merge chain. If no
  next branch was found (i.e. hasNextBranch is false), this value is null.