Pull Request Pusher should be the author of the merge (#36581)

In manual merge detected changes, the pushing user should be the
de-facto author of the merge, not the committer. For ff-only merges, the
author (PR owner) often have nothing to do with the merger. Similarly,
even if a merge commit exists, it does not indicate that the merge
commit author is the merger. This is especially true if the merge commit
is a ff-only merge on a given branch.
    
If pusher is for some reason unavailable, we fall back to the old method
of using committer or owning organization as the author.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/pull/check.go

@@ -333,6 +333,28 @@ func getMergeCommit(ctx context.Context, pr *issues_model.PullRequest) (*git.Com
 	return commit, nil
 }
 
+func getMergerForManuallyMergedPullRequest(ctx context.Context, pr *issues_model.PullRequest) (*user_model.User, error) {
+	var errs []error
+	if branch, err := git_model.GetBranch(ctx, pr.BaseRepoID, pr.BaseBranch); err != nil {
+		errs = append(errs, err)
+	} else {
+		err := branch.LoadPusher(ctx) // LoadPusher uses ghost for non-existing user
+		if branch.Pusher != nil && branch.Pusher.ID > 0 {
+			return branch.Pusher, nil
+		} else if err != nil {
+			errs = append(errs, err)
+		}
+	}
+
+	// When the doer (pusher) is unknown set the BaseRepo owner as merger
+	err := pr.BaseRepo.LoadOwner(ctx)
+	if err == nil {
+		return pr.BaseRepo.Owner, nil
+	}
+	errs = append(errs, err)
+	return nil, fmt.Errorf("unable to find merger for manually merged pull request: %w", errors.Join(errs...))
+}
+
 // manuallyMerged checks if a pull request got manually merged
 // When a pull request got manually merged mark the pull request as merged
 func manuallyMerged(ctx context.Context, pr *issues_model.PullRequest) bool {
@@ -362,18 +384,11 @@ func manuallyMerged(ctx context.Context, pr *issues_model.PullRequest) bool {
 		return false
 	}
 
-	merger, _ := user_model.GetUserByEmail(ctx, commit.Author.Email)
-
-	// When the commit author is unknown set the BaseRepo owner as merger
-	if merger == nil {
-		if pr.BaseRepo.Owner == nil {
-			if err = pr.BaseRepo.LoadOwner(ctx); err != nil {
-				log.Error("%-v BaseRepo.LoadOwner: %v", pr, err)
+	merger, err := getMergerForManuallyMergedPullRequest(ctx, pr)
+	if err != nil {
+		log.Error("%-v getMergerForManuallyMergedPullRequest: %v", pr, err)
 		return false
 	}
-		}
-		merger = pr.BaseRepo.Owner
-	}
 
 	if merged, err := SetMerged(ctx, pr, commit.ID.String(), timeutil.TimeStamp(commit.Author.When.Unix()), merger, issues_model.PullRequestStatusManuallyMerged); err != nil {
 		log.Error("%-v setMerged : %v", pr, err)

tests/integration/manual_merge_test.go

@@ -0,0 +1,75 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"fmt"
+	"net/url"
+	"testing"
+	"time"
+
+	auth_model "code.gitea.io/gitea/models/auth"
+	issues_model "code.gitea.io/gitea/models/issues"
+	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/setting"
+	api "code.gitea.io/gitea/modules/structs"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestManualMergeAutodetect(t *testing.T) {
+	onGiteaRun(t, func(t *testing.T, giteaURL *url.URL) {
+		// user2 is the repo owner
+		// user1 is the pusher/merger
+		user1 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 1})
+		user2 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+		session2 := loginUser(t, user2.Name)
+
+		// Create a repo owned by user2
+		repoName := "manual-merge-autodetect"
+		defaultBranch := setting.Repository.DefaultBranch
+		user2Ctx := NewAPITestContext(t, user2.Name, repoName, auth_model.AccessTokenScopeWriteRepository, auth_model.AccessTokenScopeWriteUser)
+		doAPICreateRepository(user2Ctx, false)(t)
+
+		// Enable autodetect manual merge
+		doAPIEditRepository(user2Ctx, &api.EditRepoOption{
+			HasPullRequests:       new(true),
+			AllowManualMerge:      new(true),
+			AutodetectManualMerge: new(true),
+		})(t)
+
+		// Create a PR from a branch
+		branchName := "feature"
+		testEditFileToNewBranch(t, session2, user2.Name, repoName, defaultBranch, branchName, "README.md", "Manual Merge Test")
+
+		apiPull, err := doAPICreatePullRequest(NewAPITestContext(t, user1.Name, repoName, auth_model.AccessTokenScopeWriteRepository), user2.Name, repoName, defaultBranch, branchName)(t)
+		assert.NoError(t, err)
+
+		// user1 clones and pushes the branch to master (fast-forward)
+		dstPath := t.TempDir()
+		u, _ := url.Parse(giteaURL.String())
+		u.Path = fmt.Sprintf("%s/%s.git", user2.Name, repoName)
+		u.User = url.UserPassword(user1.Name, userPassword)
+
+		doGitClone(dstPath, u)(t)
+		doGitMerge(dstPath, "origin/"+branchName)(t)
+		doGitPushTestRepository(dstPath, "origin", defaultBranch)(t)
+
+		// Wait for the PR to be marked as merged by the background task
+		var pr *issues_model.PullRequest
+		require.Eventually(t, func() bool {
+			pr = unittest.AssertExistsAndLoadBean(t, &issues_model.PullRequest{ID: apiPull.ID})
+			return pr.HasMerged
+		}, 10*time.Second, 100*time.Millisecond)
+
+		// Check if the PR is merged and who is the merger
+		pr = unittest.AssertExistsAndLoadBean(t, &issues_model.PullRequest{ID: apiPull.ID})
+		assert.True(t, pr.HasMerged)
+		assert.Equal(t, issues_model.PullRequestStatusManuallyMerged, pr.Status)
+		// Merger should be user1 (the pusher), not the commit author (user2) or repo owner (user2)
+		assert.Equal(t, user1.ID, pr.MergerID)
+	})
+}