Fix automerge will not work because of some events haven't been triggered (#30780)

Replace #25741
Close #24445
Close #30658
Close #20646
~Depends on #30805~

Since #25741 has been rewritten totally, to make the contribution
easier, I will continue the work in this PR. Thanks @6543

---------

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
(cherry picked from commit c6cf96d31d80ab79d370a6192fd761b4443daec2)

Conflicts:
	tests/integration/editor_test.go
	trivial context conflict because of 75ce1e2ac1 [GITEA] Allow user to select email for file operations in Web UI
	tests/integration/pull_merge_test.go
	trivial context conflicts in imports because more tests were added in Forgejo

2 files changed, 116 insertions, 38 deletions

diff --git a/services/automerge/automerge.go b/services/automerge/automerge.go
index bd1317c7f4..10f3c28d56 100644
--- a/services/automerge/automerge.go
+++ b/services/automerge/automerge.go
@@ -22,6 +22,7 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/process"
 	"code.gitea.io/gitea/modules/queue"
+	notify_service "code.gitea.io/gitea/services/notify"
 	pull_service "code.gitea.io/gitea/services/pull"
 )
 
@@ -30,6 +31,8 @@ var prAutoMergeQueue *queue.WorkerPoolQueue[string]
 
 // Init runs the task queue to that handles auto merges
 func Init() error {
+	notify_service.RegisterNotifier(NewNotifier())
+
 	prAutoMergeQueue = queue.CreateUniqueQueue(graceful.GetManager().ShutdownContext(), "pr_auto_merge", handler)
 	if prAutoMergeQueue == nil {
 		return fmt.Errorf("unable to create pr_auto_merge queue")
@@ -47,7 +50,7 @@ func handler(items ...string) []string {
 			log.Error("could not parse data from pr_auto_merge queue (%v): %v", s, err)
 			continue
 		}
-		handlePull(id, sha)
+		handlePullRequestAutoMerge(id, sha)
 	}
 	return nil
 }
@@ -62,16 +65,6 @@ func addToQueue(pr *issues_model.PullRequest, sha string) {
 // ScheduleAutoMerge if schedule is false and no error, pull can be merged directly
 func ScheduleAutoMerge(ctx context.Context, doer *user_model.User, pull *issues_model.PullRequest, style repo_model.MergeStyle, message string) (scheduled bool, err error) {
 	err = db.WithTx(ctx, func(ctx context.Context) error {
-		lastCommitStatus, err := pull_service.GetPullRequestCommitStatusState(ctx, pull)
-		if err != nil {
-			return err
-		}
-
-		// we don't need to schedule
-		if lastCommitStatus.IsSuccess() {
-			return nil
-		}
-
 		if err := pull_model.ScheduleAutoMerge(ctx, doer, pull.ID, style, message); err != nil {
 			return err
 		}
@@ -95,8 +88,8 @@ func RemoveScheduledAutoMerge(ctx context.Context, doer *user_model.User, pull *
 	})
 }
 
-// MergeScheduledPullRequest merges a previously scheduled pull request when all checks succeeded
-func MergeScheduledPullRequest(ctx context.Context, sha string, repo *repo_model.Repository) error {
+// StartPRCheckAndAutoMergeBySHA start an automerge check and auto merge task for all pull requests of repository and SHA
+func StartPRCheckAndAutoMergeBySHA(ctx context.Context, sha string, repo *repo_model.Repository) error {
 	pulls, err := getPullRequestsByHeadSHA(ctx, sha, repo, func(pr *issues_model.PullRequest) bool {
 		return !pr.HasMerged && pr.CanAutoMerge()
 	})
@@ -111,6 +104,32 @@ func MergeScheduledPullRequest(ctx context.Context, sha string, repo *repo_model
 	return nil
 }
 
+// StartPRCheckAndAutoMerge start an automerge check and auto merge task for a pull request
+func StartPRCheckAndAutoMerge(ctx context.Context, pull *issues_model.PullRequest) {
+	if pull == nil || pull.HasMerged || !pull.CanAutoMerge() {
+		return
+	}
+
+	if err := pull.LoadBaseRepo(ctx); err != nil {
+		log.Error("LoadBaseRepo: %v", err)
+		return
+	}
+
+	gitRepo, err := gitrepo.OpenRepository(ctx, pull.BaseRepo)
+	if err != nil {
+		log.Error("OpenRepository: %v", err)
+		return
+	}
+	defer gitRepo.Close()
+	commitID, err := gitRepo.GetRefCommitID(pull.GetGitRefName())
+	if err != nil {
+		log.Error("GetRefCommitID: %v", err)
+		return
+	}
+
+	addToQueue(pull, commitID)
+}
+
 func getPullRequestsByHeadSHA(ctx context.Context, sha string, repo *repo_model.Repository, filter func(*issues_model.PullRequest) bool) (map[int64]*issues_model.PullRequest, error) {
 	gitRepo, err := gitrepo.OpenRepository(ctx, repo)
 	if err != nil {
@@ -161,7 +180,8 @@ func getPullRequestsByHeadSHA(ctx context.Context, sha string, repo *repo_model.
 	return pulls, nil
 }
 
-func handlePull(pullID int64, sha string) {
+// handlePullRequestAutoMerge merge the pull request if all checks are successful
+func handlePullRequestAutoMerge(pullID int64, sha string) {
 	ctx, _, finished := process.GetManager().AddContext(graceful.GetManager().HammerContext(),
 		fmt.Sprintf("Handle AutoMerge of PR[%d] with sha[%s]", pullID, sha))
 	defer finished()
@@ -182,24 +202,50 @@ func handlePull(pullID int64, sha string) {
 		return
 	}
 
+	if err = pr.LoadBaseRepo(ctx); err != nil {
+		log.Error("%-v LoadBaseRepo: %v", pr, err)
+		return
+	}
+
+	// check the sha is the same as pull request head commit id
+	baseGitRepo, err := gitrepo.OpenRepository(ctx, pr.BaseRepo)
+	if err != nil {
+		log.Error("OpenRepository: %v", err)
+		return
+	}
+	defer baseGitRepo.Close()
+
+	headCommitID, err := baseGitRepo.GetRefCommitID(pr.GetGitRefName())
+	if err != nil {
+		log.Error("GetRefCommitID: %v", err)
+		return
+	}
+	if headCommitID != sha {
+		log.Warn("Head commit id of auto merge %-v does not match sha [%s], it may means the head branch has been updated. Just ignore this request because a new request expected in the queue", pr, sha)
+		return
+	}
+
 	// Get all checks for this pr
 	// We get the latest sha commit hash again to handle the case where the check of a previous push
 	// did not succeed or was not finished yet.
-
 	if err = pr.LoadHeadRepo(ctx); err != nil {
 		log.Error("%-v LoadHeadRepo: %v", pr, err)
 		return
 	}
 
-	headGitRepo, err := gitrepo.OpenRepository(ctx, pr.HeadRepo)
-	if err != nil {
-		log.Error("OpenRepository %-v: %v", pr.HeadRepo, err)
-		return
+	var headGitRepo *git.Repository
+	if pr.BaseRepoID == pr.HeadRepoID {
+		headGitRepo = baseGitRepo
+	} else {
+		headGitRepo, err = gitrepo.OpenRepository(ctx, pr.HeadRepo)
+		if err != nil {
+			log.Error("OpenRepository %-v: %v", pr.HeadRepo, err)
+			return
+		}
+		defer headGitRepo.Close()
 	}
-	defer headGitRepo.Close()
 
 	headBranchExist := headGitRepo.IsBranchExist(pr.HeadBranch)
-
 	if pr.HeadRepo == nil || !headBranchExist {
 		log.Warn("Head branch of auto merge %-v does not exist [HeadRepoID: %d, Branch: %s]", pr, pr.HeadRepoID, pr.HeadBranch)
 		return
@@ -238,25 +284,11 @@ func handlePull(pullID int64, sha string) {
 		return
 	}
 
-	var baseGitRepo *git.Repository
-	if pr.BaseRepoID == pr.HeadRepoID {
-		baseGitRepo = headGitRepo
-	} else {
-		if err = pr.LoadBaseRepo(ctx); err != nil {
-			log.Error("%-v LoadBaseRepo: %v", pr, err)
-			return
-		}
-
-		baseGitRepo, err = gitrepo.OpenRepository(ctx, pr.BaseRepo)
-		if err != nil {
-			log.Error("OpenRepository %-v: %v", pr.BaseRepo, err)
-			return
-		}
-		defer baseGitRepo.Close()
-	}
-
 	if err := pull_service.Merge(ctx, pr, doer, baseGitRepo, scheduledPRM.MergeStyle, "", scheduledPRM.Message, true); err != nil {
 		log.Error("pull_service.Merge: %v", err)
+		// FIXME: if merge failed, we should display some error message to the pull request page.
+		// The resolution is add a new column on automerge table named `error_message` to store the error message and displayed
+		// on the pull request page. But this should not be finished in a bug fix PR which will be backport to release branch.
 		return
 	}
 }
diff --git a/services/automerge/notify.go b/services/automerge/notify.go
new file mode 100644
index 0000000000..cb078214f6
--- /dev/null
+++ b/services/automerge/notify.go
@@ -0,0 +1,46 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package automerge
+
+import (
+	"context"
+
+	issues_model "code.gitea.io/gitea/models/issues"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/log"
+	notify_service "code.gitea.io/gitea/services/notify"
+)
+
+type automergeNotifier struct {
+	notify_service.NullNotifier
+}
+
+var _ notify_service.Notifier = &automergeNotifier{}
+
+// NewNotifier create a new automergeNotifier notifier
+func NewNotifier() notify_service.Notifier {
+	return &automergeNotifier{}
+}
+
+func (n *automergeNotifier) PullRequestReview(ctx context.Context, pr *issues_model.PullRequest, review *issues_model.Review, comment *issues_model.Comment, mentions []*user_model.User) {
+	// as a missing / blocking reviews could have blocked a pending automerge let's recheck
+	if review.Type == issues_model.ReviewTypeApprove {
+		if err := StartPRCheckAndAutoMergeBySHA(ctx, review.CommitID, pr.BaseRepo); err != nil {
+			log.Error("StartPullRequestAutoMergeCheckBySHA: %v", err)
+		}
+	}
+}
+
+func (n *automergeNotifier) PullReviewDismiss(ctx context.Context, doer *user_model.User, review *issues_model.Review, comment *issues_model.Comment) {
+	if err := review.LoadIssue(ctx); err != nil {
+		log.Error("LoadIssue: %v", err)
+		return
+	}
+	if err := review.Issue.LoadPullRequest(ctx); err != nil {
+		log.Error("LoadPullRequest: %v", err)
+		return
+	}
+	// as reviews could have blocked a pending automerge let's recheck
+	StartPRCheckAndAutoMerge(ctx, review.Issue.PullRequest)
+}