From da1d8f4e7c332c7109427915e6459b10209cedce Mon Sep 17 00:00:00 2001
From: Runxi Yu <me@runxiyu.org>
Date: Sun, 6 Apr 2025 09:26:46 +0800
Subject: Move the Go stuff to ./forged/

---
 forged/internal/oldgit/patch.go | 42 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 forged/internal/oldgit/patch.go

(limited to 'forged/internal/oldgit/patch.go')

diff --git a/forged/internal/oldgit/patch.go b/forged/internal/oldgit/patch.go
new file mode 100644
index 0000000..30bf8e8
--- /dev/null
+++ b/forged/internal/oldgit/patch.go
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+// SPDX-FileCopyrightText: Copyright (c) 2025 Runxi Yu <https://runxiyu.org>
+
+package oldgit
+
+import (
+	"errors"
+
+	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/plumbing/object"
+)
+
+// CommitToPatch creates an [object.Patch] from the first parent of a given
+// [object.Commit].
+//
+// TODO: This function should be deprecated as it only diffs with the first
+// parent and does not correctly handle merge commits.
+func CommitToPatch(commit *object.Commit) (parentCommitHash plumbing.Hash, patch *object.Patch, err error) {
+	var parentCommit *object.Commit
+	var commitTree *object.Tree
+
+	parentCommit, err = commit.Parent(0)
+	switch {
+	case errors.Is(err, object.ErrParentNotFound):
+		if commitTree, err = commit.Tree(); err != nil {
+			return
+		}
+		if patch, err = NullTree.Patch(commitTree); err != nil {
+			return
+		}
+	case err != nil:
+		return
+	default:
+		parentCommitHash = parentCommit.Hash
+		if patch, err = parentCommit.Patch(commit); err != nil {
+			return
+		}
+	}
+	return
+}
+
+var NullTree object.Tree //nolint:gochecknoglobals
-- 
cgit v1.2.3