feat: shallow clone action repositories (#1053)

## Summary

When a workflow references a remote action (e.g. `uses: actions/checkout@v4`) the runner clones that repository during job setup.
Previously this was always a full clone(every branch and the complete history) even though only a single ref is needed.

This PR makes the runner shallow-clone the requested ref by default (`--depth=1`, single branch), falling back to a full clone when a shallow clone fails.

Notes:
- Existing on-disk caches are reused as-is; there is no forced re-clone on upgrade.

## Changes

- A new `runner.action_shallow_clone` option (default `true`) lets operators opt back into full clones.
- `cloneAtDepth`: attempt a shallow clone; fall back to a full clone when shallow clone fails.
- Keep a shallow cache cheap on update: fetch the single requested ref at depth 1 and skip `pull`.

---------

Co-authored-by: bircni <bircni@icloud.com>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1053
Reviewed-by: Nicolas <bircni@icloud.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>
Co-committed-by: Zettat123 <zettat123@gmail.com>

act/common/git/git_test.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"sync"
 	"syscall"
@@ -380,6 +381,96 @@ func TestGitCloneExecutorOfflineMode(t *testing.T) {
 	})
 }
 
+func TestGitCloneExecutorShallow(t *testing.T) {
+	// Build a local "remote" with several commits on main plus a tag, so a full clone would pull noticeably more history than a shallow one.
+	remoteDir := t.TempDir()
+	require.NoError(t, gitCmd("init", "--bare", "--initial-branch=main", remoteDir))
+	workDir := t.TempDir()
+	require.NoError(t, gitCmd("clone", remoteDir, workDir))
+	require.NoError(t, gitCmd("-C", workDir, "checkout", "-b", "main"))
+	for _, m := range []string{"c1", "c2", "c3"} {
+		require.NoError(t, gitCmd("-C", workDir, "commit", "--allow-empty", "-m", m))
+	}
+	require.NoError(t, gitCmd("-C", workDir, "tag", "v1"))
+	sha := gitRevParse(t, workDir, "HEAD~1") // c2, a SHA that go-git cannot shallow-clone
+	require.NoError(t, gitCmd("-C", workDir, "push", "-u", "origin", "main"))
+	require.NoError(t, gitCmd("-C", workDir, "push", "origin", "v1"))
+
+	shallowMarker := func(dir string) string { return filepath.Join(dir, ".git", "shallow") }
+
+	t.Run("branch is cloned shallowly", func(t *testing.T) {
+		dir := t.TempDir()
+		require.NoError(t, NewGitCloneExecutor(NewGitCloneExecutorInput{
+			URL: remoteDir, Ref: "main", Dir: dir, Depth: 1,
+		})(t.Context()))
+		assert.FileExists(t, shallowMarker(dir), "clone should be shallow")
+		assert.Equal(t, 1, gitRevCount(t, dir), "only the tip commit should be present")
+		assert.Equal(t, "c3", gitHeadSubject(t, dir))
+	})
+
+	t.Run("tag is cloned shallowly", func(t *testing.T) {
+		dir := t.TempDir()
+		require.NoError(t, NewGitCloneExecutor(NewGitCloneExecutorInput{
+			URL: remoteDir, Ref: "v1", Dir: dir, Depth: 1,
+		})(t.Context()))
+		assert.FileExists(t, shallowMarker(dir), "clone should be shallow")
+		assert.Equal(t, 1, gitRevCount(t, dir))
+		assert.Equal(t, "c3", gitHeadSubject(t, dir))
+	})
+
+	t.Run("SHA falls back to a full clone", func(t *testing.T) {
+		dir := t.TempDir()
+		require.NoError(t, NewGitCloneExecutor(NewGitCloneExecutorInput{
+			URL: remoteDir, Ref: sha, Dir: dir, Depth: 1,
+		})(t.Context()))
+		// go-git cannot shallow-clone a raw SHA, so it falls back to a full clone; the absence of a shallow marker proves the fallback happened.
+		assert.NoFileExists(t, shallowMarker(dir), "a SHA ref must not produce a shallow clone")
+		assert.Equal(t, sha, gitRevParse(t, dir, "HEAD"))
+	})
+
+	t.Run("moving branch updates while staying shallow", func(t *testing.T) {
+		dir := t.TempDir()
+		require.NoError(t, NewGitCloneExecutor(NewGitCloneExecutorInput{
+			URL: remoteDir, Ref: "main", Dir: dir, Depth: 1,
+		})(t.Context()))
+		require.Equal(t, "c3", gitHeadSubject(t, dir))
+
+		// Advance main on the remote, then reuse the existing shallow clone.
+		require.NoError(t, gitCmd("-C", workDir, "commit", "--allow-empty", "-m", "c4"))
+		require.NoError(t, gitCmd("-C", workDir, "push", "origin", "main"))
+
+		require.NoError(t, NewGitCloneExecutor(NewGitCloneExecutorInput{
+			URL: remoteDir, Ref: "main", Dir: dir, Depth: 1,
+		})(t.Context()))
+		assert.Equal(t, "c4", gitHeadSubject(t, dir), "reused shallow clone should update to the new tip")
+		assert.FileExists(t, shallowMarker(dir), "repo should remain shallow after update")
+		assert.Equal(t, 1, gitRevCount(t, dir))
+	})
+}
+
+func gitRevParse(t *testing.T, dir, rev string) string {
+	t.Helper()
+	out, err := exec.Command("git", "-C", dir, "rev-parse", rev).Output()
+	require.NoError(t, err)
+	return strings.TrimSpace(string(out))
+}
+
+func gitRevCount(t *testing.T, dir string) int {
+	t.Helper()
+	out, err := exec.Command("git", "-C", dir, "rev-list", "--count", "HEAD").Output()
+	require.NoError(t, err)
+	n, err := strconv.Atoi(strings.TrimSpace(string(out)))
+	require.NoError(t, err)
+	return n
+}
+
+func gitHeadSubject(t *testing.T, dir string) string {
+	t.Helper()
+	out, err := exec.Command("git", "-C", dir, "log", "-1", "--format=%s").Output()
+	require.NoError(t, err)
+	return strings.TrimSpace(string(out))
+}
+
 func gitCmd(args ...string) error {
 	cmd := exec.Command("git", args...)
 	cmd.Stdout = os.Stdout