Prevent simultaneous editing of comments and issues (#31053)

fixes #22907 

Tested:
- [x] issue content edit
- [x] issue content change tasklist
- [x] pull request content edit
- [x] pull request change tasklist

![issue-content-edit](https://github.com/go-gitea/gitea/assets/29250154/a0828889-fb96-4bc4-8600-da92e3205812)

3 files changed, 22 insertions, 5 deletions

diff --git a/models/issues/comment.go b/models/issues/comment.go
index 336bdde58e..c6c5dc2432 100644
--- a/models/issues/comment.go
+++ b/models/issues/comment.go
@@ -52,6 +52,8 @@ func (err ErrCommentNotExist) Unwrap() error {
 	return util.ErrNotExist
 }
 
+var ErrCommentAlreadyChanged = util.NewInvalidArgumentErrorf("the comment is already changed")
+
 // CommentType defines whether a comment is just a simple comment, an action (like close) or a reference.
 type CommentType int
 
@@ -262,6 +264,7 @@ type Comment struct {
 	Line            int64 // - previous line / + proposed line
 	TreePath        string
 	Content         string        `xorm:"LONGTEXT"`
+	ContentVersion  int           `xorm:"NOT NULL DEFAULT 0"`
 	RenderedContent template.HTML `xorm:"-"`
 
 	// Path represents the 4 lines of code cemented by this comment
@@ -1111,7 +1114,7 @@ func UpdateCommentInvalidate(ctx context.Context, c *Comment) error {
 }
 
 // UpdateComment updates information of comment.
-func UpdateComment(ctx context.Context, c *Comment, doer *user_model.User) error {
+func UpdateComment(ctx context.Context, c *Comment, contentVersion int, doer *user_model.User) error {
 	ctx, committer, err := db.TxContext(ctx)
 	if err != nil {
 		return err
@@ -1119,9 +1122,15 @@ func UpdateComment(ctx context.Context, c *Comment, doer *user_model.User) error
 	defer committer.Close()
 	sess := db.GetEngine(ctx)
 
-	if _, err := sess.ID(c.ID).AllCols().Update(c); err != nil {
+	c.ContentVersion = contentVersion + 1
+
+	affected, err := sess.ID(c.ID).AllCols().Where("content_version = ?", contentVersion).Update(c)
+	if err != nil {
 		return err
 	}
+	if affected == 0 {
+		return ErrCommentAlreadyChanged
+	}
 	if err := c.LoadIssue(ctx); err != nil {
 		return err
 	}
diff --git a/models/issues/issue.go b/models/issues/issue.go
index 87c1c86eb1..aad855522d 100644
--- a/models/issues/issue.go
+++ b/models/issues/issue.go
@@ -94,6 +94,8 @@ func (err ErrIssueWasClosed) Error() string {
 	return fmt.Sprintf("Issue [%d] %d was already closed", err.ID, err.Index)
 }
 
+var ErrIssueAlreadyChanged = util.NewInvalidArgumentErrorf("the issue is already changed")
+
 // Issue represents an issue or pull request of repository.
 type Issue struct {
 	ID               int64                  `xorm:"pk autoincr"`
@@ -107,6 +109,7 @@ type Issue struct {
 	Title            string                 `xorm:"name"`
 	Content          string                 `xorm:"LONGTEXT"`
 	RenderedContent  template.HTML          `xorm:"-"`
+	ContentVersion   int                    `xorm:"NOT NULL DEFAULT 0"`
 	Labels           []*Label               `xorm:"-"`
 	MilestoneID      int64                  `xorm:"INDEX"`
 	Milestone        *Milestone             `xorm:"-"`
diff --git a/models/issues/issue_update.go b/models/issues/issue_update.go
index 147b7eb3b9..31d76be5e0 100644
--- a/models/issues/issue_update.go
+++ b/models/issues/issue_update.go
@@ -235,7 +235,7 @@ func UpdateIssueAttachments(ctx context.Context, issueID int64, uuids []string)
 }
 
 // ChangeIssueContent changes issue content, as the given user.
-func ChangeIssueContent(ctx context.Context, issue *Issue, doer *user_model.User, content string) (err error) {
+func ChangeIssueContent(ctx context.Context, issue *Issue, doer *user_model.User, content string, contentVersion int) (err error) {
 	ctx, committer, err := db.TxContext(ctx)
 	if err != nil {
 		return err
@@ -254,9 +254,14 @@ func ChangeIssueContent(ctx context.Context, issue *Issue, doer *user_model.User
 	}
 
 	issue.Content = content
+	issue.ContentVersion = contentVersion + 1
 
-	if err = UpdateIssueCols(ctx, issue, "content"); err != nil {
-		return fmt.Errorf("UpdateIssueCols: %w", err)
+	affected, err := db.GetEngine(ctx).ID(issue.ID).Cols("content", "content_version").Where("content_version = ?", contentVersion).Update(issue)
+	if err != nil {
+		return err
+	}
+	if affected == 0 {
+		return ErrIssueAlreadyChanged
 	}
 
 	if err = SaveIssueContentHistory(ctx, doer.ID, issue.ID, 0,