fix!: use the git CLI for action clones and make builtin:checkout match actions/checkout (#1277)

The runner now uses the `git` command line instead of go-git to download actions and reusable workflows. go-git had recurring bugs and does not support SHA-256 repositories, and full clones of actions are several times faster.

`builtin:checkout` now runs `git` where the job runs and behaves like `actions/checkout`:

1. A branch is checked out as a local branch tracking `origin`, tag and pull request runs keep their ref, and a triggering tag that moved fails the step.
1. Later steps can fetch and push with the persisted token or SSH key.
1. It supports the `ssh-*`, `lfs`, `submodules`, `sparse-checkout`, `filter`, `fetch-tags`, `clean`, `persist-credentials`, `show-progress` and `set-safe-directory` inputs and the `ref` and `commit` outputs.
1. SHA-256 repositories work for actions, reusable workflows and `builtin:checkout`.

Git keeps the token off its command line, ignores `GIT_DIR` and similar variables inherited by the runner, and keeps action files LF regardless of `core.autocrlf`. A cancelled job lets git remove its lock files.

This is a breaking change: the runner needs Git 2.34.1 or newer on its `PATH`, and so do job images that use `builtin:checkout`. The official runner images include it.

Fixes: https://gitea.com/gitea/runner/issues/1077
Fixes: https://gitea.com/gitea/runner/issues/1267
Fixes: https://gitea.com/gitea/runner/issues/1279
Fixes: https://gitea.com/gitea/runner/issues/1284
Fixes: https://gitea.com/gitea/runner/issues/1285
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: silverwind <2021+silverwind@noreply.gitea.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1277
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Co-authored-by: bircni <bircni@icloud.com>

docs/builtin-actions.md

@@ -8,14 +8,32 @@ Built-in actions ship with the runner, so a job needs no action download and no
 
 ## checkout
 
-Works like `actions/checkout` with these inputs. Any other input fails the step.
+Works like `actions/checkout` with these inputs. Any other input fails the step. It runs `git` where the job runs, see the [prerequisites](../README.md#prerequisites).
 
 | Input | Default |
 | --- | --- |
 | `repository` | `github.repository` |
-| `ref` | the triggering commit, or the default branch of another repository |
+| `ref` | the triggering ref and commit, or the default branch of another repository |
 | `token` | `github.token` |
+| `ssh-key` | empty, a private key fetches over SSH instead |
+| `ssh-known-hosts` | empty, host keys trusted besides `~/.ssh/known_hosts` |
+| `ssh-strict` | `true`, rejects unknown host keys |
+| `ssh-user` | the user of the repository's SSH URL, else `git` |
+| `persist-credentials` | `true`, later steps of the job can fetch and push with `token` or `ssh-key` |
 | `path` | workspace root |
-| `fetch-depth` | `1`, `0` for full history |
+| `clean` | `true`, removes untracked files, also in submodules |
+| `filter` | empty, a partial clone filter such as `blob:none` |
+| `sparse-checkout` | empty, the paths to check out, one per line |
+| `sparse-checkout-cone-mode` | `true`, `false` reads `sparse-checkout` as patterns |
+| `fetch-depth` | `1`, `0` for the full history of every branch and tag |
+| `fetch-tags` | `false`, `true` fetches every tag |
+| `show-progress` | `true`, shows the fetch progress |
+| `lfs` | `false`, `true` downloads Git LFS files |
+| `submodules` | `false`, `true` checks out submodules, `recursive` also theirs |
+| `set-safe-directory` | `true`, lets checkout's `git` work in a directory another user owns |
 
-With `gitea-runner exec`, checking out the workflow's own repository copies your local working directory, unless `--no-skip-checkout` is set.
+A branch is checked out as a local branch tracking `origin`, a tag or commit as a detached `HEAD`. A triggering tag that moved since the event fails the step. The step outputs `ref` and `commit` like `actions/checkout`.
+
+Persisted credentials end with the job. `token` is only sent to `github.server_url`, while `ssh-key` is offered to any SSH host, as with `actions/checkout`. Without `ssh-key`, submodule URLs of the form `git@<server host>:` are fetched from `github.server_url` with `token`. With `ssh-key`, the repository is fetched from the SSH URL in the event's `repository.ssh_url`, or from the server's host on port 22.
+
+With `gitea-runner exec`, checking out the workflow's own repository copies your local working directory, unless `--no-skip-checkout` or `ssh-key` is set.