localrepo: Support porcelain fetch option

When performing `git-fetch(1)` with the `porcelain` option, references
are printed to stdout in an easy-to-parse format. This change introduces
a `localrepo.FetchRemote()` configuration to enabled `porcelain` output.

2 files changed, 39 insertions, 0 deletions

diff --git a/internal/git/localrepo/remote.go b/internal/git/localrepo/remote.go
index 737ba230d..696512afb 100644
--- a/internal/git/localrepo/remote.go
+++ b/internal/git/localrepo/remote.go
@@ -52,6 +52,10 @@ type FetchOpts struct {
 	Tags FetchOptsTags
 	// DryRun, if enabled, performs the `git-fetch(1)` command without updating any references.
 	DryRun bool
+	// Porcelain controls `git-fetch(1)` command output and when enabled prints output in an
+	// easy-to-parse format. By default, `git-fetch(1)` output is suppressed by the `--quiet` flag.
+	// Therefore, the Verbose option must also be enabled to receive output.
+	Porcelain bool
 	// Stdout if set it would be used to redirect stdout stream into it.
 	Stdout io.Writer
 	// Stderr if set it would be used to redirect stderr stream into it.
@@ -207,6 +211,10 @@ func (opts FetchOpts) buildFlags() []git.Option {
 		flags = append(flags, git.Flag{Name: "--dry-run"})
 	}
 
+	if opts.Porcelain {
+		flags = append(flags, git.Flag{Name: "--porcelain"})
+	}
+
 	// Even if we ask Git to not print any output and to force-update branches it will still
 	// compute whether branches have been force-updated only to discard that information again.
 	// Let's ask it not to given that this check can be quite expensive.
diff --git a/internal/git/localrepo/remote_test.go b/internal/git/localrepo/remote_test.go
index 25c4e7ddc..138428253 100644
--- a/internal/git/localrepo/remote_test.go
+++ b/internal/git/localrepo/remote_test.go
@@ -188,6 +188,37 @@ func TestRepo_FetchRemote(t *testing.T) {
 		require.Len(t, refs, 0)
 	})
 
+	t.Run("with porcelain", func(t *testing.T) {
+		repo, _ := initBareWithRemote(t, "origin")
+
+		// The porcelain fetch option write output to stdout in an easy-to-parse format. By default,
+		// output is suppressed by the --quiet flag. The Verbose option must also be enabled to
+		// receive output.
+		var stdout bytes.Buffer
+		require.NoError(t, repo.FetchRemote(ctx, "origin", FetchOpts{
+			Stdout:    &stdout,
+			Porcelain: true,
+			Verbose:   true,
+		}))
+
+		hash, err := repo.ObjectHash(ctx)
+		require.NoError(t, err)
+		scanner := git.NewFetchPorcelainScanner(&stdout, hash)
+
+		// Scan the output for expected references.
+		require.True(t, scanner.Scan())
+		require.Equal(t, git.RefUpdateTypeFetched, scanner.StatusLine().Type)
+		require.Equal(t, "refs/remotes/origin/main", scanner.StatusLine().Reference)
+		require.True(t, scanner.Scan())
+		require.Equal(t, git.RefUpdateTypeFetched, scanner.StatusLine().Type)
+		require.Equal(t, "refs/tags/v1.0.0", scanner.StatusLine().Reference)
+
+		// Since the remote only contains two references, there should be nothing left in the buffer
+		// to scan.
+		require.False(t, scanner.Scan())
+		require.Nil(t, scanner.Err())
+	})
+
 	t.Run("with no tags", func(t *testing.T) {
 		repo, testRepoPath := initBareWithRemote(t, "origin")