From 7ab5e5fc5c91d66f04a2dd256592a4f8db255bce Mon Sep 17 00:00:00 2001
From: Lewis <lewis@tangled.org>
Date: Wed, 1 Apr 2026 14:56:57 +0300
Subject: [PATCH] knotserver/xrpc: merge-base for combined patch in repo
 compare

Lewis: May this revision serve well! <lewis@tangled.org>
---
 knotserver/git/cmd.go           |  4 ++++
 knotserver/git/diff.go          | 10 ++++++++++
 knotserver/xrpc/repo_compare.go | 11 ++++++++---
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/knotserver/git/cmd.go b/knotserver/git/cmd.go
index 0a5dec73..b359d7a4 100644
--- a/knotserver/git/cmd.go
+++ b/knotserver/git/cmd.go
@@ -40,3 +40,7 @@ func (g *GitRepo) forEachRef(extraArgs ...string) ([]byte, error) {
 func (g *GitRepo) revParse(extraArgs ...string) ([]byte, error) {
 	return g.runGitCmd("rev-parse", extraArgs...)
 }
+
+func (g *GitRepo) mergeBase(extraArgs ...string) ([]byte, error) {
+	return g.runGitCmd("merge-base", extraArgs...)
+}
diff --git a/knotserver/git/diff.go b/knotserver/git/diff.go
index e5ccd1f8..b58e2d3d 100644
--- a/knotserver/git/diff.go
+++ b/knotserver/git/diff.go
@@ -77,6 +77,16 @@ func (g *GitRepo) Diff() (*types.NiceDiff, error) {
 	return &nd, nil
 }
 
+func (g *GitRepo) MergeBase(a, b *object.Commit) (*object.Commit, error) {
+	out, err := g.mergeBase(a.Hash.String(), b.Hash.String())
+	if err != nil {
+		return nil, fmt.Errorf("merge-base %s %s: %w", a.Hash, b.Hash, err)
+	}
+
+	hash := plumbing.NewHash(strings.TrimSpace(string(out)))
+	return g.r.CommitObject(hash)
+}
+
 func (g *GitRepo) DiffTree(commit1, commit2 *object.Commit) (*types.DiffTree, error) {
 	tree1, err := commit1.Tree()
 	if err != nil {
diff --git a/knotserver/xrpc/repo_compare.go b/knotserver/xrpc/repo_compare.go
index aeb23a1a..2d4bde31 100644
--- a/knotserver/xrpc/repo_compare.go
+++ b/knotserver/xrpc/repo_compare.go
@@ -76,12 +76,17 @@ func (x *Xrpc) RepoCompare(w http.ResponseWriter, r *http.Request) {
 	var combinedPatchRaw string
 	// we need the combined patch
 	if len(formatPatch) >= 2 {
-		diffTree, err := gr.DiffTree(commit1, commit2)
+		mergeBaseCommit, err := gr.MergeBase(commit1, commit2)
 		if err != nil {
 			x.Logger.Error("error comparing revisions", "msg", err.Error())
 		} else {
-			combinedPatch = diffTree.Diff
-			combinedPatchRaw = diffTree.Patch
+			diffTree, err := gr.DiffTree(mergeBaseCommit, commit2)
+			if err != nil {
+				x.Logger.Error("error comparing revisions", "msg", err.Error())
+			} else {
+				combinedPatch = diffTree.Diff
+				combinedPatchRaw = diffTree.Patch
+			}
 		}
 	}
 
-- 
2.51.2