From a8ef5d5125955b6c76ef8d30d5be6221e8e0a477 Mon Sep 17 00:00:00 2001
From: badhezi <zlilaharon@gmail.com>
Date: Mon, 2 Jun 2025 11:53:01 +0300
Subject: [PATCH] make head repo selection clearer

---
 routers/web/repo/compare.go       | 26 ++++++++++++++++++--------
 tests/integration/compare_test.go |  2 +-
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/routers/web/repo/compare.go b/routers/web/repo/compare.go
index 846064b4166..7fb99925b9d 100644
--- a/routers/web/repo/compare.go
+++ b/routers/web/repo/compare.go
@@ -247,13 +247,13 @@ func ParseCompareInfo(ctx *context.Context) *common.CompareInfo {
 
 	// If there is no head repository, it means compare between the same repository.
 	headInfos := strings.Split(infos[1], ":")
-	if len(headInfos) == 1 {
+	if len(headInfos) == 1 { // {:headBranch} case, guaranteed baseRepo is headRepo
 		isSameRepo = true
 		ci.HeadUser = ctx.Repo.Owner
-		ci.HeadBranch, ci.RawDiffType = parseRefForRawDiff(ctx, ctx.Repo.Repository, headInfos[0])
-	} else if len(headInfos) == 2 {
+		ci.HeadBranch, ci.RawDiffType = parseRefForRawDiff(ctx, baseRepo, headInfos[0])
+	} else if len(headInfos) == 2 { // {:headOwner}:{:headBranch} or {:headOwner}/{:headRepoName}:{:headBranch} case
 		headInfosSplit := strings.Split(headInfos[0], "/")
-		if len(headInfosSplit) == 1 {
+		if len(headInfosSplit) == 1 { // {:headOwner}:{:headBranch} case, guaranteed baseRepo.Name is headRepo.Name
 			ci.HeadUser, err = user_model.GetUserByName(ctx, headInfos[0])
 			if err != nil {
 				if user_model.IsErrUserNotExist(err) {
@@ -263,13 +263,23 @@ func ParseCompareInfo(ctx *context.Context) *common.CompareInfo {
 				}
 				return nil
 			}
-			// FIXME: how to correctly choose the head repository? The logic below (3-8) is quite complex, the real head repo is determined there
-			ci.HeadBranch, ci.RawDiffType = parseRefForRawDiff(ctx, ..., headInfos[1])
+
+			headRepo, err := repo_model.GetRepositoryByOwnerAndName(ctx, ci.HeadUser.Name, baseRepo.Name)
+			if err != nil {
+				if repo_model.IsErrRepoNotExist(err) {
+					ctx.NotFound(nil)
+				} else {
+					ctx.ServerError("GetRepositoryByOwnerAndName", err)
+				}
+				return nil
+			}
+			ci.HeadBranch, ci.RawDiffType = parseRefForRawDiff(ctx, headRepo, headInfos[1])
+
 			isSameRepo = ci.HeadUser.ID == ctx.Repo.Owner.ID
-			if isSameRepo {
+			if isSameRepo { // not a fork
 				ci.HeadRepo = baseRepo
 			}
-		} else {
+		} else { // {:headOwner}/{:headRepoName}:{:headBranch} case, across forks
 			ci.HeadRepo, err = repo_model.GetRepositoryByOwnerAndName(ctx, headInfosSplit[0], headInfosSplit[1])
 			if err != nil {
 				if repo_model.IsErrRepoNotExist(err) {
diff --git a/tests/integration/compare_test.go b/tests/integration/compare_test.go
index f0304de9b75..08e0f285563 100644
--- a/tests/integration/compare_test.go
+++ b/tests/integration/compare_test.go
@@ -229,7 +229,7 @@ func TestCompareRawDiffPatch(t *testing.T) {
 		respTs = respTs.In(time.Local)
 
 		// Format the timestamp to match the expected format in the patch
-		customFormat := "Mon, 02 Jan 2006 15:04:05 -0700"
+		customFormat := "Mon, 2 Jan 2006 15:04:05 -0700"
 		respTsStr := respTs.Format(customFormat)
 
 		req := NewRequest(t, "GET", fmt.Sprintf("/user1/test_raw_diff/compare/%s...%s.patch", oldRef.ID.String(), newRef.ID.String()))