# 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 ```yaml repository: description: 'Repository name with owner. For example, actions/checkout' default: ${{ github.repository }} ref: description: > The branch, tag or SHA to checkout. When checking out the repository that triggered a workflow, this defaults to the reference or SHA for that event. Otherwise, uses the default branch. token: description: > Personal access token (PAT) used to fetch the repository. The PAT is configured with the local git config, which enables your scripts to run authenticated git commands. The post-job step removes the PAT. We recommend using a service account with the least permissions necessary. Also when generating a new PAT, select the least scopes necessary. [Learn more about creating and using encrypted secrets](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/creating-and-using-encrypted-secrets) default: ${{ github.token }} ssh-key: description: > SSH key used to fetch the repository. The SSH key is configured with the local git config, which enables your scripts to run authenticated git commands. The post-job step removes the SSH key. We recommend using a service account with the least permissions necessary. [Learn more about creating and using encrypted secrets](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/creating-and-using-encrypted-secrets) ssh-known-hosts: description: > Known hosts in addition to the user and global host key database. The public SSH keys for a host may be obtained using the utility `ssh-keyscan`. For example, `ssh-keyscan github.com`. The public key for github.com is always implicitly added. ssh-strict: description: > Whether to perform strict host key checking. When true, adds the options `StrictHostKeyChecking=yes` and `CheckHostIP=no` to the SSH command line. Use the input `ssh-known-hosts` to configure additional hosts. default: true persist-credentials: description: 'Whether to configure the token or SSH key with the local git config' default: true path: description: 'Relative or absolute path under $GITHUB_WORKSPACE to place the repository' clean: description: 'Whether to execute `git clean -ffdx && git reset --hard HEAD` before fetching' default: true fetch-depth: description: 'Number of commits to fetch. 0 indicates all history for all tags and branches.' default: 1 lfs: description: 'Whether to download Git-LFS files' default: false submodules: description: > Whether to checkout submodules: `true` to checkout submodules or `recursive` to recursively checkout submodules. When the `ssh-key` input is not provided, SSH URLs beginning with `git@github.com:` are converted to HTTPS. default: false ``` Note: - SSH support is new - `persist-credentials` is new - `path` behavior is different (refer [below](#path) for details) ### Fallback to GitHub API When a sufficient version of git is not in the PATH, fallback to the [web API](https://developer.github.com/v3/repos/contents/#get-archive-link) to download a tarball/zipball. Note: - LFS files are not included in the archive. Therefore fail if LFS is set to true. - Submodules are also not included in the archive. ### Persist credentials The credentials will be persisted on disk. This will allow users to script authenticated git commands, like `git fetch`. A post script will remove the credentials (cleanup for self-hosted). Users may opt-out by specifying `persist-credentials: false` Note: - Users scripting `git commit` may need to set the username and email. The service does not provide any reasonable default value. Users can add `git config user.name ` and `git config user.email `. We will document this guidance. #### PAT When using the `${{github.token}}` or a PAT, the token will be persisted in the local git config. The config key `http.https://github.com/.extraheader` enables an auth header to be specified on all authenticated commands `AUTHORIZATION: basic `. Note: - The auth header 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. #### SSH key The SSH key will be written to disk under the `$RUNNER_TEMP` directory. The SSH key will be removed by the action's post-job hook. Additionally, RUNNER_TEMP is cleared by the runner between jobs. The SSH key must be written with strict file permissions. The SSH client requires the file to be read/write for the user, and not accessible by others. The user host key database (`~/.ssh/known_hosts`) will be copied to a unique file under `$RUNNER_TEMP`. And values from the input `ssh-known-hosts` will be added to the file. The SSH command will be overridden for the local git config: ```sh git config core.sshCommand 'ssh -i "$RUNNER_TEMP/path-to-ssh-key" -o StrictHostKeyChecking=yes -o CheckHostIP=no -o "UserKnownHostsFile=$RUNNER_TEMP/path-to-known-hosts"' ``` When the input `ssh-strict` is set to `false`, the options `CheckHostIP` and `StrictHostKeyChecking` will not be overridden. Note: - When `ssh-strict` is set to `true` (default), the SSH option `CheckHostIP` can safely be disabled. Strict host checking verifies the server's public key. Therefore, IP verification is unnecessary and noisy. For example: > Warning: Permanently added the RSA host key for IP address '140.82.113.4' to the list of known hosts. - Since GIT_SSH_COMMAND overrides core.sshCommand, temporarily set the env var when fetching the repo. When creds are persisted, core.sshCommand is leveraged to avoid multiple checkout steps stomping over each other. - Modify actions/runner to mount RUNNER_TEMP to enable scripting authenticated git commands from a container action. - Refer [here](https://linux.die.net/man/5/ssh_config) for SSH config details. ### Fetch behavior 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. The input `fetch-depth` can be used to control the depth. Note: - 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 behavior 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. ### Submodules With both PAT and SSH key support, we should be able to provide frictionless support for submodules scenarios: recursive, non-recursive, relative submodule paths. When fetching submodules, follow the `fetch-depth` settings. Also when fetching submodules, if the `ssh-key` input is not provided then convert SSH URLs to HTTPS: `-c url."https://github.com/".insteadOf "git@github.com:"` Credentials will be persisted in the submodules local git config too. ### 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 the default branch - 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)