Move database operations of merging a pull request to post receive hook and add a transaction (#30805)

Merging PR may fail because of various problems. The pull request may
have a dirty state because there is no transaction when merging a pull
request. ref
https://github.com/go-gitea/gitea/pull/25741#issuecomment-2074126393

This PR moves all database update operations to post-receive handler for
merging a pull request and having a database transaction. That means if
database operations fail, then the git merging will fail, the git client
will get a fail result.

There are already many tests for pull request merging, so we don't need
to add a new one.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
(cherry picked from commit ebf0c969403d91ed80745ff5bd7dfbdb08174fc7)

Conflicts:
	modules/private/hook.go
	routers/private/hook_post_receive.go
	trivial conflicts because
	  263a716cb5 * Performance optimization for git push (#30104)
	was not cherry-picked and because of
	  998a431747a15cc95f7056a2029b736551eb037b Do not update PRs based on events that happened before they existed

2 files changed, 112 insertions, 0 deletions

diff --git a/routers/private/hook_post_receive.go b/routers/private/hook_post_receive.go
index 381e3c6c77..10b300f3df 100644
--- a/routers/private/hook_post_receive.go
+++ b/routers/private/hook_post_receive.go
@@ -4,20 +4,26 @@
 package private
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 	"strconv"
 	"time"
 
+	"code.gitea.io/gitea/models/db"
 	git_model "code.gitea.io/gitea/models/git"
 	issues_model "code.gitea.io/gitea/models/issues"
+	pull_model "code.gitea.io/gitea/models/pull"
 	repo_model "code.gitea.io/gitea/models/repo"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/cache"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/gitrepo"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/private"
 	repo_module "code.gitea.io/gitea/modules/repository"
 	"code.gitea.io/gitea/modules/setting"
+	timeutil "code.gitea.io/gitea/modules/timeutil"
 	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/modules/web"
 	gitea_context "code.gitea.io/gitea/services/context"
@@ -155,6 +161,14 @@ func HookPostReceive(ctx *gitea_context.PrivateContext) {
 		}
 	}
 
+	// handle pull request merging, a pull request action should push at least 1 commit
+	if opts.PushTrigger == repo_module.PushTriggerPRMergeToBase {
+		handlePullRequestMerging(ctx, opts, ownerName, repoName, updates)
+		if ctx.Written() {
+			return
+		}
+	}
+
 	// Handle Push Options
 	if len(opts.GitPushOptions) > 0 {
 		// load the repository
@@ -302,3 +316,52 @@ func HookPostReceive(ctx *gitea_context.PrivateContext) {
 		RepoWasEmpty: wasEmpty,
 	})
 }
+
+func loadContextCacheUser(ctx context.Context, id int64) (*user_model.User, error) {
+	return cache.GetWithContextCache(ctx, "hook_post_receive_user", id, func() (*user_model.User, error) {
+		return user_model.GetUserByID(ctx, id)
+	})
+}
+
+// handlePullRequestMerging handle pull request merging, a pull request action should push at least 1 commit
+func handlePullRequestMerging(ctx *gitea_context.PrivateContext, opts *private.HookOptions, ownerName, repoName string, updates []*repo_module.PushUpdateOptions) {
+	if len(updates) == 0 {
+		ctx.JSON(http.StatusInternalServerError, private.HookPostReceiveResult{
+			Err: fmt.Sprintf("Pushing a merged PR (pr:%d) no commits pushed ", opts.PullRequestID),
+		})
+		return
+	}
+
+	pr, err := issues_model.GetPullRequestByID(ctx, opts.PullRequestID)
+	if err != nil {
+		log.Error("GetPullRequestByID[%d]: %v", opts.PullRequestID, err)
+		ctx.JSON(http.StatusInternalServerError, private.HookPostReceiveResult{Err: "GetPullRequestByID failed"})
+		return
+	}
+
+	pusher, err := loadContextCacheUser(ctx, opts.UserID)
+	if err != nil {
+		log.Error("Failed to Update: %s/%s Error: %v", ownerName, repoName, err)
+		ctx.JSON(http.StatusInternalServerError, private.HookPostReceiveResult{Err: "Load pusher user failed"})
+		return
+	}
+
+	pr.MergedCommitID = updates[len(updates)-1].NewCommitID
+	pr.MergedUnix = timeutil.TimeStampNow()
+	pr.Merger = pusher
+	pr.MergerID = pusher.ID
+	err = db.WithTx(ctx, func(ctx context.Context) error {
+		// Removing an auto merge pull and ignore if not exist
+		if err := pull_model.DeleteScheduledAutoMerge(ctx, pr.ID); err != nil && !db.IsErrNotExist(err) {
+			return fmt.Errorf("DeleteScheduledAutoMerge[%d]: %v", opts.PullRequestID, err)
+		}
+		if _, err := pr.SetMerged(ctx); err != nil {
+			return fmt.Errorf("SetMerged failed: %s/%s Error: %v", ownerName, repoName, err)
+		}
+		return nil
+	})
+	if err != nil {
+		log.Error("Failed to update PR to merged: %v", err)
+		ctx.JSON(http.StatusInternalServerError, private.HookPostReceiveResult{Err: "Failed to update PR to merged"})
+	}
+}
diff --git a/routers/private/hook_post_receive_test.go b/routers/private/hook_post_receive_test.go
new file mode 100644
index 0000000000..658557d3cf
--- /dev/null
+++ b/routers/private/hook_post_receive_test.go
@@ -0,0 +1,49 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package private
+
+import (
+	"testing"
+
+	"code.gitea.io/gitea/models/db"
+	issues_model "code.gitea.io/gitea/models/issues"
+	pull_model "code.gitea.io/gitea/models/pull"
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/private"
+	repo_module "code.gitea.io/gitea/modules/repository"
+	"code.gitea.io/gitea/services/contexttest"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestHandlePullRequestMerging(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+	pr, err := issues_model.GetUnmergedPullRequest(db.DefaultContext, 1, 1, "branch2", "master", issues_model.PullRequestFlowGithub)
+	assert.NoError(t, err)
+	assert.NoError(t, pr.LoadBaseRepo(db.DefaultContext))
+
+	user1 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 1})
+
+	err = pull_model.ScheduleAutoMerge(db.DefaultContext, user1, pr.ID, repo_model.MergeStyleSquash, "squash merge a pr")
+	assert.NoError(t, err)
+
+	autoMerge := unittest.AssertExistsAndLoadBean(t, &pull_model.AutoMerge{PullID: pr.ID})
+
+	ctx, resp := contexttest.MockPrivateContext(t, "/")
+	handlePullRequestMerging(ctx, &private.HookOptions{
+		PullRequestID: pr.ID,
+		UserID:        2,
+	}, pr.BaseRepo.OwnerName, pr.BaseRepo.Name, []*repo_module.PushUpdateOptions{
+		{NewCommitID: "01234567"},
+	})
+	assert.Equal(t, 0, len(resp.Body.String()))
+	pr, err = issues_model.GetPullRequestByID(db.DefaultContext, pr.ID)
+	assert.NoError(t, err)
+	assert.True(t, pr.HasMerged)
+	assert.EqualValues(t, "01234567", pr.MergedCommitID)
+
+	unittest.AssertNotExistsBean(t, &pull_model.AutoMerge{ID: autoMerge.ID})
+}