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
	  998a431747 Do not update PRs based on events that happened before they existed

cmd/hook.go

@@ -366,6 +366,7 @@ Forgejo or set your environment appropriately.`, "")
 	isWiki, _ := strconv.ParseBool(os.Getenv(repo_module.EnvRepoIsWiki))
 	repoName := os.Getenv(repo_module.EnvRepoName)
 	pusherID, _ := strconv.ParseInt(os.Getenv(repo_module.EnvPusherID), 10, 64)
+	prID, _ := strconv.ParseInt(os.Getenv(repo_module.EnvPRID), 10, 64)
 	pusherName := os.Getenv(repo_module.EnvPusherName)
 
 	hookOptions := private.HookOptions{
@@ -375,6 +376,8 @@ Forgejo or set your environment appropriately.`, "")
 		GitObjectDirectory:              os.Getenv(private.GitObjectDirectory),
 		GitQuarantinePath:               os.Getenv(private.GitQuarantinePath),
 		GitPushOptions:                  pushOptions(),
+		PullRequestID:                   prID,
+		PushTrigger:                     repo_module.PushTrigger(os.Getenv(repo_module.EnvPushTrigger)),
 	}
 	oldCommitIDs := make([]string, hookBatchSize)
 	newCommitIDs := make([]string, hookBatchSize)

modules/private/hook.go

@@ -11,6 +11,7 @@ import (
 	"time"
 
 	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/repository"
 	"code.gitea.io/gitea/modules/setting"
 )
 
@@ -53,6 +54,7 @@ type HookOptions struct {
 	GitQuarantinePath               string
 	GitPushOptions                  GitPushOptions
 	PullRequestID                   int64
+	PushTrigger                     repository.PushTrigger
 	DeployKeyID                     int64 // if the pusher is a DeployKey, then UserID is the repo's org user.
 	IsWiki                          bool
 	ActionPerm                      int

modules/repository/env.go

@@ -25,11 +25,19 @@ const (
 	EnvKeyID        = "GITEA_KEY_ID" // public key ID
 	EnvDeployKeyID  = "GITEA_DEPLOY_KEY_ID"
 	EnvPRID         = "GITEA_PR_ID"
+	EnvPushTrigger  = "GITEA_PUSH_TRIGGER"
 	EnvIsInternal   = "GITEA_INTERNAL_PUSH"
 	EnvAppURL       = "GITEA_ROOT_URL"
 	EnvActionPerm   = "GITEA_ACTION_PERM"
 )
 
+type PushTrigger string
+
+const (
+	PushTriggerPRMergeToBase    PushTrigger = "pr-merge-to-base"
+	PushTriggerPRUpdateWithBase PushTrigger = "pr-update-with-base"
+)
+
 // InternalPushingEnvironment returns an os environment to switch off hooks on push
 // It is recommended to avoid using this unless you are pushing within a transaction
 // or if you absolutely are sure that post-receive and pre-receive will do nothing

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"})
+	}
+}

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})
+}

services/contexttest/context_tests.go

@@ -86,6 +86,19 @@ func MockAPIContext(t *testing.T, reqPath string) (*context.APIContext, *httptes
 	return ctx, resp
 }
 
+func MockPrivateContext(t *testing.T, reqPath string) (*context.PrivateContext, *httptest.ResponseRecorder) {
+	resp := httptest.NewRecorder()
+	req := mockRequest(t, reqPath)
+	base, baseCleanUp := context.NewBaseContext(resp, req)
+	base.Data = middleware.GetContextData(req.Context())
+	base.Locale = &translation.MockLocale{}
+	ctx := &context.PrivateContext{Base: base}
+	_ = baseCleanUp // during test, it doesn't need to do clean up. TODO: this can be improved later
+	chiCtx := chi.NewRouteContext()
+	ctx.Base.AppendContextValue(chi.RouteCtxKey, chiCtx)
+	return ctx, resp
+}
+
 // LoadRepo load a repo into a test context.
 func LoadRepo(t *testing.T, ctx gocontext.Context, repoID int64) {
 	var doer *user_model.User

services/pull/merge.go

@@ -18,7 +18,6 @@ import (
 	git_model "code.gitea.io/gitea/models/git"
 	issues_model "code.gitea.io/gitea/models/issues"
 	access_model "code.gitea.io/gitea/models/perm/access"
-	pull_model "code.gitea.io/gitea/models/pull"
 	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/models/unit"
 	user_model "code.gitea.io/gitea/models/user"
@@ -168,12 +167,6 @@ func Merge(ctx context.Context, pr *issues_model.PullRequest, doer *user_model.U
 	pullWorkingPool.CheckIn(fmt.Sprint(pr.ID))
 	defer pullWorkingPool.CheckOut(fmt.Sprint(pr.ID))
 
-	// Removing an auto merge pull and ignore if not exist
-	// FIXME: is this the correct point to do this? Shouldn't this be after IsMergeStyleAllowed?
-	if err := pull_model.DeleteScheduledAutoMerge(ctx, pr.ID); err != nil && !db.IsErrNotExist(err) {
-		return err
-	}
-
 	prUnit, err := pr.BaseRepo.GetUnit(ctx, unit.TypePullRequests)
 	if err != nil {
 		log.Error("pr.BaseRepo.GetUnit(unit.TypePullRequests): %v", err)
@@ -190,17 +183,15 @@ func Merge(ctx context.Context, pr *issues_model.PullRequest, doer *user_model.U
 		AddTestPullRequestTask(ctx, doer, pr.BaseRepo.ID, pr.BaseBranch, false, "", "", 0)
 	}()
 
-	pr.MergedCommitID, err = doMergeAndPush(ctx, pr, doer, mergeStyle, expectedHeadCommitID, message)
+	_, err = doMergeAndPush(ctx, pr, doer, mergeStyle, expectedHeadCommitID, message, repo_module.PushTriggerPRMergeToBase)
 	if err != nil {
 		return err
 	}
 
-	pr.MergedUnix = timeutil.TimeStampNow()
-	pr.Merger = doer
-	pr.MergerID = doer.ID
-
-	if _, err := pr.SetMerged(ctx); err != nil {
-		log.Error("SetMerged %-v: %v", pr, err)
+	// reload pull request because it has been updated by post receive hook
+	pr, err = issues_model.GetPullRequestByID(ctx, pr.ID)
+	if err != nil {
+		return err
 	}
 
 	if err := pr.LoadIssue(ctx); err != nil {
@@ -251,7 +242,7 @@ func Merge(ctx context.Context, pr *issues_model.PullRequest, doer *user_model.U
 }
 
 // doMergeAndPush performs the merge operation without changing any pull information in database and pushes it up to the base repository
-func doMergeAndPush(ctx context.Context, pr *issues_model.PullRequest, doer *user_model.User, mergeStyle repo_model.MergeStyle, expectedHeadCommitID, message string) (string, error) {
+func doMergeAndPush(ctx context.Context, pr *issues_model.PullRequest, doer *user_model.User, mergeStyle repo_model.MergeStyle, expectedHeadCommitID, message string, pushTrigger repo_module.PushTrigger) (string, error) {
 	// Clone base repo.
 	mergeCtx, cancel, err := createTemporaryRepoForMerge(ctx, pr, doer, expectedHeadCommitID)
 	if err != nil {
@@ -324,11 +315,13 @@ func doMergeAndPush(ctx context.Context, pr *issues_model.PullRequest, doer *use
 		pr.BaseRepo.Name,
 		pr.ID,
 	)
+
+	mergeCtx.env = append(mergeCtx.env, repo_module.EnvPushTrigger+"="+string(pushTrigger))
 	pushCmd := git.NewCommand(ctx, "push", "origin").AddDynamicArguments(baseBranch + ":" + git.BranchPrefix + pr.BaseBranch)
 
 	// Push back to upstream.
-	// TODO: this cause an api call to "/api/internal/hook/post-receive/...",
-	//       that prevents us from doint the whole merge in one db transaction
+	// This cause an api call to "/api/internal/hook/post-receive/...",
+	// If it's merge, all db transaction and operations should be there but not here to prevent deadlock.
 	if err := pushCmd.Run(mergeCtx.RunOpts()); err != nil {
 		if strings.Contains(mergeCtx.errbuf.String(), "non-fast-forward") {
 			return "", &git.ErrPushOutOfDate{

services/pull/update.go

@@ -15,6 +15,7 @@ import (
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/repository"
 )
 
 // Update updates pull request with base branch.
@@ -72,7 +73,7 @@ func Update(ctx context.Context, pr *issues_model.PullRequest, doer *user_model.
 		BaseBranch: pr.HeadBranch,
 	}
 
-	_, err = doMergeAndPush(ctx, reversePR, doer, repo_model.MergeStyleMerge, "", message)
+	_, err = doMergeAndPush(ctx, reversePR, doer, repo_model.MergeStyleMerge, "", message, repository.PushTriggerPRUpdateWithBase)
 
 	defer func() {
 		AddTestPullRequestTask(ctx, doer, reversePR.HeadRepo.ID, reversePR.HeadBranch, false, "", "", 0)