Attach a refs/notes/byre note to each squash merge and push it

internal/git/git.go

@@ -3,6 +3,7 @@ package git
 import (
 	"errors"
 	"fmt"
+	"io"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -217,8 +218,8 @@ const Remote = "origin"
 
 var ErrRemoteMoved = errors.New("the remote's branch has moved")
 
-func Push(repo, commit, branch string) error {
-	out, stderr, code, err := runCode(repo, nil, "push", "--porcelain", Remote, commit+":refs/heads/"+branch)
+func Push(repo, commit, branch, notes string) error {
+	out, stderr, code, err := runCode(repo, nil, "push", "--atomic", "--porcelain", Remote, commit+":refs/heads/"+branch, notes+":"+NotesRef)
 	if err != nil {
 		return err
 	}
@@ -239,7 +240,7 @@ func FastForward(repo, rev string) error {
 }
 
 func FetchFastForward(repo, branch string) error {
-	_, err := run(repo, "fetch", Remote, branch)
+	_, err := run(repo, "fetch", Remote)
 	if err != nil {
 		return err
 	}
@@ -303,10 +304,26 @@ func runEnv(dir string, env []string, args ...string) (string, error) {
 	return out, nil
 }
 
+func runInput(dir string, env []string, input string, args ...string) (string, error) {
+	out, stderr, code, err := runCodeInput(dir, env, strings.NewReader(input), args...)
+	if err != nil {
+		return "", err
+	}
+	if code != 0 {
+		return "", fmt.Errorf("git %s: exit status %d: %s", strings.Join(args, " "), code, stderr)
+	}
+	return out, nil
+}
+
 func runCode(dir string, env []string, args ...string) (string, string, int, error) {
+	return runCodeInput(dir, env, nil, args...)
+}
+
+func runCodeInput(dir string, env []string, stdin io.Reader, args ...string) (string, string, int, error) {
 	cmd := exec.Command("git", args...)
 	cmd.Dir = dir
 	cmd.Env = append(os.Environ(), env...)
+	cmd.Stdin = stdin
 	stderr := &strings.Builder{}
 	cmd.Stderr = stderr
 	out, err := cmd.Output()

internal/git/notes.go

@@ -0,0 +1,75 @@
+package git
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"slices"
+	"strings"
+)
+
+const NotesRef = "refs/notes/byre"
+
+const notesFetch = NotesRef + "*:" + NotesRef + "*"
+
+func ConfigureNotesFetch(repo string) error {
+	key := "remote." + Remote + ".fetch"
+	out, stderr, code, err := runCode(repo, nil, "config", "--get-all", key)
+	if err != nil {
+		return err
+	}
+	if code != 0 && code != 1 {
+		return fmt.Errorf("git config --get-all %s: exit status %d: %s", key, code, stderr)
+	}
+	if slices.Contains(strings.Split(out, "\n"), notesFetch) {
+		return nil
+	}
+	_, err = run(repo, "config", "--add", key, notesFetch)
+	return err
+}
+
+func NoteCommit(repo, commit, note string, env []string) (string, error) {
+	blob, err := runInput(repo, nil, note, "hash-object", "-w", "--stdin")
+	if err != nil {
+		return "", err
+	}
+
+	parent, stderr, code, err := runCode(repo, nil, "rev-parse", "--verify", "--quiet", NotesRef)
+	if err != nil {
+		return "", err
+	}
+	if code != 0 && code != 1 {
+		return "", fmt.Errorf("git rev-parse %s: exit status %d: %s", NotesRef, code, stderr)
+	}
+
+	dir, err := os.MkdirTemp("", "byre-notes-*")
+	if err != nil {
+		return "", err
+	}
+	defer os.RemoveAll(dir)
+	index := []string{"GIT_INDEX_FILE=" + filepath.Join(dir, "index")}
+
+	commitArgs := []string{"commit-tree", "-m", "Notes added by byre"}
+	if code == 0 {
+		_, err = runEnv(repo, index, "read-tree", parent)
+		if err != nil {
+			return "", err
+		}
+		commitArgs = append(commitArgs, "-p", parent)
+	}
+	_, err = runEnv(repo, index, "update-index", "--add", "--cacheinfo", "100644,"+blob+","+commit)
+	if err != nil {
+		return "", err
+	}
+	tree, err := runEnv(repo, index, "write-tree")
+	if err != nil {
+		return "", err
+	}
+
+	return runEnv(repo, env, append(commitArgs, tree)...)
+}
+
+func SetNotes(repo, notes string) error {
+	_, err := run(repo, "update-ref", NotesRef, notes)
+	return err
+}