# ADR 0153: Checkout v2 **Date**: 2019-10-21 **Status**: Accepted ## Context This ADR details the behavior for `actions/checkout@v2`. The new action will be written in typescript. We are moving away from runner-plugin actions. We want to take this opportunity to make behavioral changes, from v1. This document is scoped to those differences. ## Decision ### Inputs - `repository` - The qualified repository name (owner/repo) - Defaults to the workflow repo - `ref` - The ref to checkout - For the workflow repo, defaults to the branch and sha from the workflow event payload - Otherwise defaults to `master` - `token` - Defaults to the job token - `persist-credentials` - Indicates whether to embed the auth token into the git config. Allows users to script authenticated git commands. - Defaults to `true` - `clean` - Indicates whether to run `git clean -ffdx && git reset --hard` - Defaults to `true` - `lfs` - Indicates whether to download Git-LFS files - Defaults to `false` - `path` - Relative path under the `github.workspace` where the repository should be created - Defaults to the `github.workspace` Note: - `persist-credentials` is new - `fetch-depth` was removed (refer [below](#fetch) for details) - `path` behavior is different (refer [below](#path) for details) - `submodules` was removed (error if specified; add later if needed) ### Fallback to GitHub API When a sufficient version of git is not in the PATH, fallback to the [web API](https://developer.github.com/v3/repos/contents/#get-archive-link) to download a tarball/zipball. Note: - LFS files are not included in the archive. Therefore fail if LFS is set to true. - Submodules are also not included in the archive. However submodules are not supported by checkout v2 anyway. ### Persist credentials Persist the token in the git config (http.extraheader). This will allow users to script authenticated git commands, like `git fetch`. A post script will remove the credentials from the git config (cleanup for self-hosted). Users may opt-out by specifying `persist-credentials: false` Note: - Users scripting `git commit` may need to set the username and email. The service does not provide any reasonable default value. Users can add `git config user.name ` and `git config user.email `. We will document this guidance. - The auth header (stored in the repo's git config), is scoped to all of github `http.https://github.com/.extraheader` - Additional public remotes also just work. - If users want to authenticate to an additional private remote, they should provide the `token` input. - Lines up if we add submodule support in the future. Don't need to worry about calculating relative URLs. Just works, although needs to be persisted in each submodule git config. - Users opt out of persisted credentials (`persist-credentials: false`), or can script the removal themselves (`git config --unset-all http.https://github.com/.extraheader`). ### Fetch Fetch only the SHA being built and set depth=1. This significantly reduces the fetch time for large repos. If a SHA isn't available (e.g. multi repo), then fetch only the specified ref with depth=1. Customers can run `git fetch --unshallow` to fetch all refs/commits. We will document this guidance. Note: - The v1 input `fetch-depth` no longer exists. We can add this back in the future if needed. - Fetching a single commit is supported by Git wire protocol version 2. The git client uses protocol version 0 by default. The desired protocol version can be overridden in the git config or on the fetch command line invocation (`-c protocol.version=2`). We will override on the fetch command line, for transparency. - Git client version 2.18+ (released June 2018) is required for wire protocol version 2. ### Checkout For CI, checkout will create a local ref with the upstream set. This allows users to script git as they normally would. For PR, continue to checkout detached head. The PR branch is special - the branch and merge commit are created by the server. It doesn't match a users' local workflow. Note: - Consider deleting all local refs during cleanup if that helps avoid collisions. More testing required. ### Path For the mainline scenario, the disk-layout behavior remains the same. Remember, given the repo `johndoe/foo`, the mainline disk layout looks like: ``` GITHUB_WORKSPACE=/home/runner/work/foo/foo RUNNER_WORKSPACE=/home/runner/work/foo ``` V2 introduces a new contraint on the checkout path. The location must now be under `github.workspace`. Whereas the checkout@v1 constraint was one level up, under `runner.workspace`. V2 no longer changes `github.workspace` to follow wherever the self repo is checked-out. These behavioral changes align better with container actions. The [documented filesystem contract](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/virtual-environments-for-github-hosted-runners#docker-container-filesystem) is: - `/github/home` - `/github/workspace` - Note: GitHub Actions must be run by the default Docker user (root). Ensure your Dockerfile does not set the USER instruction, otherwise you will not be able to access `GITHUB_WORKSPACE`. - `/github/workflow` Note: - The tracking config will not be updated to reflect the path of the workflow repo. - Any existing workflow repo will not be moved when the checkout path changes. In fact some customers want to checkout the workflow repo twice, side by side against different branches. - Actions that need to operate only against the root of the self repo, should expose a `path` input. #### Default value for `path` input The `path` input will default to `./` which is rooted against `github.workspace`. This default fits the mainline scenario well: single checkout For multi-checkout, users must specify the `path` input for at least one of the repositories. Note: - An alternative is for the self repo to default to `./` and other repos default to ``. However nested layout is an atypical git layout and therefore is not a good default. Users should supply the path info. #### Example - Nested layout The following example checks-out two repositories and creates a nested layout. ```yaml # Self repo - Checkout to $GITHUB_WORKSPACE - uses: checkout@v2 # Other repo - Checkout to $GITHUB_WORKSPACE/myscripts - uses: checkout@v2 with: repository: myorg/myscripts path: myscripts ``` #### Example - Side by side layout The following example checks-out two repositories and creates a side-by-side layout. ```yaml # Self repo - Checkout to $GITHUB_WORKSPACE/foo - uses: checkout@v2 with: path: foo # Other repo - Checkout to $GITHUB_WORKSPACE/myscripts - uses: checkout@v2 with: repository: myorg/myscripts path: myscripts ``` #### Path impact to problem matchers Problem matchers associate the source files with annotations. Today the runner verifies the source file is under the `github.workspace`. Otherwise the source file property is dropped. Multi-checkout complicates the matter. However even today submodules may cause this heuristic to be inaccurate. A better solution is: Given a source file path, walk up the directories until the first `.git/config` is found. Check if it matches the self repo (`url = https://github.com/OWNER/REPO`). If not, drop the source file path. ### Port to typescript The checkout action should be a typescript action on the GitHub graph, for the following reasons: - Enables customers to fork the checkout repo and modify - Serves as an example for customers - Demystifies the checkout action manifest - Simplifies the runner - Reduce the amount of runner code to port (if we ever do) Note: - This means job-container images will need git in the PATH, for checkout. ### Branching strategy and release tags - Create a servicing branch for V1: `releases/v1` - Merge the changes into `master` - Release using a new tag `preview` - When stable, release using a new tag `v2` ## Consequences - Update the checkout action and readme - Update samples to consume `actions/checkout@v2` - Job containers now require git in the PATH for checkout, otherwise fallback to REST API - Minimum git version 2.18 - Update problem matcher logic regarding source file verification (runner)