internal/gitutil/merge.go

  1package gitutil
  2
  3import (
  4	"fmt"
  5	"os"
  6	"os/exec"
  7	"strings"
  8)
  9
 10// FetchInto copies srcRef from srcDir into dstDir as dstRef, forcing the
 11// update. Objects are copied, not shared — the destination owns everything
 12// afterward, which is what keeps MRs alive when their fork is deleted.
 13func FetchInto(dstDir, srcDir, srcRef, dstRef string) error {
 14	cmd := exec.Command("git", "-C", dstDir, "fetch", "--quiet", "--no-write-fetch-head",
 15		srcDir, "+"+srcRef+":"+dstRef)
 16	if out, err := cmd.CombinedOutput(); err != nil {
 17		return fmt.Errorf("fetch %s from %s: %v\n%s", srcRef, srcDir, err, out)
 18	}
 19	return nil
 20}
 21
 22// UpdateRefCAS points ref at newSHA only if it currently points at oldSHA
 23// (empty oldSHA = must not exist). This is the compare-and-swap that makes
 24// merges safe against concurrent pushes.
 25func UpdateRefCAS(dir, ref, newSHA, oldSHA string) error {
 26	args := []string{"-C", dir, "update-ref", ref, newSHA}
 27	if oldSHA != "" {
 28		args = append(args, oldSHA)
 29	}
 30	cmd := exec.Command("git", args...)
 31	if out, err := cmd.CombinedOutput(); err != nil {
 32		return fmt.Errorf("update-ref %s: %v\n%s", ref, err, out)
 33	}
 34	return nil
 35}
 36
 37func DeleteRef(dir, ref string) error {
 38	cmd := exec.Command("git", "-C", dir, "update-ref", "-d", ref)
 39	if out, err := cmd.CombinedOutput(); err != nil {
 40		return fmt.Errorf("delete-ref %s: %v\n%s", ref, err, out)
 41	}
 42	return nil
 43}
 44
 45// RevListRange returns commits in old..new, newest first.
 46func RevListRange(dir, old, new string) ([]string, error) {
 47	cmd := exec.Command("git", "-C", dir, "rev-list", new, "^"+old)
 48	out, err := cmd.Output()
 49	if err != nil {
 50		return nil, fmt.Errorf("rev-list %s..%s: %w", old, new, err)
 51	}
 52	var shas []string
 53	for _, l := range strings.Split(strings.TrimSpace(string(out)), "\n") {
 54		if l != "" {
 55			shas = append(shas, l)
 56		}
 57	}
 58	return shas, nil
 59}
 60
 61// MergeTree performs a real merge of ours and theirs, returning the merged
 62// tree id. conflict=true means the merge cannot be done automatically.
 63func MergeTree(dir, ours, theirs string) (tree string, conflict bool, err error) {
 64	cmd := exec.Command("git", "-C", dir, "merge-tree", "--write-tree", ours, theirs)
 65	out, runErr := cmd.Output()
 66	tree = strings.TrimSpace(strings.SplitN(string(out), "\n", 2)[0])
 67	if runErr != nil {
 68		if ee, ok := runErr.(*exec.ExitError); ok && ee.ExitCode() == 1 {
 69			return "", true, nil // conflicted merge
 70		}
 71		return "", false, fmt.Errorf("merge-tree: %w", runErr)
 72	}
 73	return tree, false, nil
 74}
 75
 76// CommitTree creates a merge commit with the given parents, authored and
 77// committed by the merging user. There is no server signing key by design.
 78func CommitTree(dir, tree string, parents []string, name, email, message string) (string, error) {
 79	args := []string{"-C", dir, "commit-tree", tree, "-m", message}
 80	for _, p := range parents {
 81		args = append(args, "-p", p)
 82	}
 83	cmd := exec.Command("git", args...)
 84	cmd.Env = append(os.Environ(),
 85		"GIT_AUTHOR_NAME="+name, "GIT_AUTHOR_EMAIL="+email,
 86		"GIT_COMMITTER_NAME="+name, "GIT_COMMITTER_EMAIL="+email,
 87	)
 88	out, err := cmd.Output()
 89	if err != nil {
 90		return "", fmt.Errorf("commit-tree: %w", err)
 91	}
 92	return strings.TrimSpace(string(out)), nil
 93}
 94
 95// Diff returns the patch for old..new (three-dot semantics are the caller's
 96// job: pass the merge base as old).
 97func Diff(dir, old, new string, limit int64) (string, error) {
 98	cmd := exec.Command("git", "-C", dir, "diff", "--stat", "--patch", old, new)
 99	out, err := cmd.Output()
100	if err != nil {
101		return "", fmt.Errorf("diff: %w", err)
102	}
103	if int64(len(out)) > limit {
104		out = out[:limit]
105	}
106	return string(out), nil
107}
108
109// MergeBase returns the best common ancestor, or an error if none exists.
110func MergeBase(dir, a, b string) (string, error) {
111	cmd := exec.Command("git", "-C", dir, "merge-base", a, b)
112	out, err := cmd.Output()
113	if err != nil {
114		return "", fmt.Errorf("no common history between %s and %s", a, b)
115	}
116	return strings.TrimSpace(string(out)), nil
117}