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)

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
 	}

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:"-"`

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 {
+	affected, err := db.GetEngine(ctx).ID(issue.ID).Cols("content", "content_version").Where("content_version = ?", contentVersion).Update(issue)
-		return fmt.Errorf("UpdateIssueCols: %w", err)
+	if err != nil {
+		return err
+	}
+	if affected == 0 {
+		return ErrIssueAlreadyChanged
 	}
 
 	if err = SaveIssueContentHistory(ctx, doer.ID, issue.ID, 0,

models/migrations/migrations.go

@@ -21,6 +21,7 @@ import (
 	"code.gitea.io/gitea/models/migrations/v1_20"
 	"code.gitea.io/gitea/models/migrations/v1_21"
 	"code.gitea.io/gitea/models/migrations/v1_22"
+	"code.gitea.io/gitea/models/migrations/v1_23"
 	"code.gitea.io/gitea/models/migrations/v1_6"
 	"code.gitea.io/gitea/models/migrations/v1_7"
 	"code.gitea.io/gitea/models/migrations/v1_8"
@@ -587,6 +588,9 @@ var migrations = []Migration{
 	NewMigration("Drop wrongly created table o_auth2_application", v1_22.DropWronglyCreatedTable),
 
 	// Gitea 1.22.0-rc1 ends at 299
+
+	// v299 -> v300
+	NewMigration("Add content version to issue and comment table", v1_23.AddContentVersionToIssueAndComment),
 }
 
 // GetCurrentDBVersion returns the current db version

models/migrations/v1_23/v299.go

@@ -0,0 +1,18 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_23 //nolint
+
+import "xorm.io/xorm"
+
+func AddContentVersionToIssueAndComment(x *xorm.Engine) error {
+	type Issue struct {
+		ContentVersion int `xorm:"NOT NULL DEFAULT 0"`
+	}
+
+	type Comment struct {
+		ContentVersion int `xorm:"NOT NULL DEFAULT 0"`
+	}
+
+	return x.Sync(new(Comment), new(Issue))
+}

options/locale/locale_en-US.ini

@@ -1443,6 +1443,7 @@ issues.new.clear_assignees = Clear assignees
 issues.new.no_assignees = No Assignees
 issues.new.no_reviewers = No reviewers
 issues.new.blocked_user = Cannot create issue because you are blocked by the repository owner.
+issues.edit.already_changed = Unable to save changes to the issue. It appears the content has already been changed by another user. Please refresh the page and try editing again to avoid overwriting their changes
 issues.edit.blocked_user = Cannot edit content because you are blocked by the poster or repository owner.
 issues.choose.get_started = Get Started
 issues.choose.open_external_link = Open
@@ -1758,6 +1759,7 @@ compare.compare_head = compare
 pulls.desc = Enable pull requests and code reviews.
 pulls.new = New Pull Request
 pulls.new.blocked_user = Cannot create pull request because you are blocked by the repository owner.
+pulls.edit.already_changed = Unable to save changes to the pull request. It appears the content has already been changed by another user. Please refresh the page and try editing again to avoid overwriting their changes
 pulls.view = View Pull Request
 pulls.compare_changes = New Pull Request
 pulls.allow_edits_from_maintainers = Allow edits from maintainers
@@ -1903,6 +1905,8 @@ pulls.recently_pushed_new_branches = You pushed on branch <strong>%[1]s</strong>
 
 pull.deleted_branch = (deleted):%s
 
+comments.edit.already_changed = Unable to save changes to the comment. It appears the content has already been changed by another user. Please refresh the page and try editing again to avoid overwriting their changes
+
 milestones.new = New Milestone
 milestones.closed = Closed %s
 milestones.update_ago = Updated %s

routers/api/v1/repo/issue.go

@@ -810,8 +810,13 @@ func EditIssue(ctx *context.APIContext) {
 		}
 	}
 	if form.Body != nil {
-		err = issue_service.ChangeContent(ctx, issue, ctx.Doer, *form.Body)
+		err = issue_service.ChangeContent(ctx, issue, ctx.Doer, *form.Body, issue.ContentVersion)
 		if err != nil {
+			if errors.Is(err, issues_model.ErrIssueAlreadyChanged) {
+				ctx.Error(http.StatusBadRequest, "ChangeContent", err)
+				return
+			}
+
 			ctx.Error(http.StatusInternalServerError, "ChangeContent", err)
 			return
 		}

routers/api/v1/repo/issue_attachment.go

@@ -198,7 +198,7 @@ func CreateIssueAttachment(ctx *context.APIContext) {
 
 	issue.Attachments = append(issue.Attachments, attachment)
 
-	if err := issue_service.ChangeContent(ctx, issue, ctx.Doer, issue.Content); err != nil {
+	if err := issue_service.ChangeContent(ctx, issue, ctx.Doer, issue.Content, issue.ContentVersion); err != nil {
 		ctx.Error(http.StatusInternalServerError, "ChangeContent", err)
 		return
 	}

routers/api/v1/repo/issue_comment.go

@@ -611,7 +611,7 @@ func editIssueComment(ctx *context.APIContext, form api.EditIssueCommentOption)
 
 	oldContent := comment.Content
 	comment.Content = form.Body
-	if err := issue_service.UpdateComment(ctx, comment, ctx.Doer, oldContent); err != nil {
+	if err := issue_service.UpdateComment(ctx, comment, comment.ContentVersion, ctx.Doer, oldContent); err != nil {
 		if errors.Is(err, user_model.ErrBlockedUser) {
 			ctx.Error(http.StatusForbidden, "UpdateComment", err)
 		} else {

routers/api/v1/repo/issue_comment_attachment.go

@@ -210,7 +210,7 @@ func CreateIssueCommentAttachment(ctx *context.APIContext) {
 		return
 	}
 
-	if err = issue_service.UpdateComment(ctx, comment, ctx.Doer, comment.Content); err != nil {
+	if err = issue_service.UpdateComment(ctx, comment, comment.ContentVersion, ctx.Doer, comment.Content); err != nil {
 		if errors.Is(err, user_model.ErrBlockedUser) {
 			ctx.Error(http.StatusForbidden, "UpdateComment", err)
 		} else {

routers/api/v1/repo/pull.go

@@ -610,8 +610,13 @@ func EditPullRequest(ctx *context.APIContext) {
 		}
 	}
 	if form.Body != nil {
-		err = issue_service.ChangeContent(ctx, issue, ctx.Doer, *form.Body)
+		err = issue_service.ChangeContent(ctx, issue, ctx.Doer, *form.Body, issue.ContentVersion)
 		if err != nil {
+			if errors.Is(err, issues_model.ErrIssueAlreadyChanged) {
+				ctx.Error(http.StatusBadRequest, "ChangeContent", err)
+				return
+			}
+
 			ctx.Error(http.StatusInternalServerError, "ChangeContent", err)
 			return
 		}

routers/web/repo/issue.go

@@ -2247,9 +2247,15 @@ func UpdateIssueContent(ctx *context.Context) {
 		return
 	}
 
-	if err := issue_service.ChangeContent(ctx, issue, ctx.Doer, ctx.Req.FormValue("content")); err != nil {
+	if err := issue_service.ChangeContent(ctx, issue, ctx.Doer, ctx.Req.FormValue("content"), ctx.FormInt("content_version")); err != nil {
 		if errors.Is(err, user_model.ErrBlockedUser) {
 			ctx.JSONError(ctx.Tr("repo.issues.edit.blocked_user"))
+		} else if errors.Is(err, issues_model.ErrIssueAlreadyChanged) {
+			if issue.IsPull {
+				ctx.JSONError(ctx.Tr("repo.pulls.edit.already_changed"))
+			} else {
+				ctx.JSONError(ctx.Tr("repo.issues.edit.already_changed"))
+			}
 		} else {
 			ctx.ServerError("ChangeContent", err)
 		}
@@ -2278,8 +2284,9 @@ func UpdateIssueContent(ctx *context.Context) {
 	}
 
 	ctx.JSON(http.StatusOK, map[string]any{
-		"content":     content,
+		"content":        content,
-		"attachments": attachmentsHTML(ctx, issue.Attachments, issue.Content),
+		"contentVersion": issue.ContentVersion,
+		"attachments":    attachmentsHTML(ctx, issue.Attachments, issue.Content),
 	})
 }
 
@@ -3153,12 +3160,15 @@ func UpdateCommentContent(ctx *context.Context) {
 
 	oldContent := comment.Content
 	newContent := ctx.FormString("content")
+	contentVersion := ctx.FormInt("content_version")
 
 	// allow to save empty content
 	comment.Content = newContent
-	if err = issue_service.UpdateComment(ctx, comment, ctx.Doer, oldContent); err != nil {
+	if err = issue_service.UpdateComment(ctx, comment, contentVersion, ctx.Doer, oldContent); err != nil {
 		if errors.Is(err, user_model.ErrBlockedUser) {
 			ctx.JSONError(ctx.Tr("repo.issues.comment.blocked_user"))
+		} else if errors.Is(err, issues_model.ErrCommentAlreadyChanged) {
+			ctx.JSONError(ctx.Tr("repo.comments.edit.already_changed"))
 		} else {
 			ctx.ServerError("UpdateComment", err)
 		}
@@ -3198,8 +3208,9 @@ func UpdateCommentContent(ctx *context.Context) {
 	}
 
 	ctx.JSON(http.StatusOK, map[string]any{
-		"content":     renderedContent,
+		"content":        renderedContent,
-		"attachments": attachmentsHTML(ctx, comment.Attachments, comment.Content),
+		"contentVersion": comment.ContentVersion,
+		"attachments":    attachmentsHTML(ctx, comment.Attachments, comment.Content),
 	})
 }
 

services/issue/comments.go

@@ -82,7 +82,7 @@ func CreateIssueComment(ctx context.Context, doer *user_model.User, repo *repo_m
 }
 
 // UpdateComment updates information of comment.
-func UpdateComment(ctx context.Context, c *issues_model.Comment, doer *user_model.User, oldContent string) error {
+func UpdateComment(ctx context.Context, c *issues_model.Comment, contentVersion int, doer *user_model.User, oldContent string) error {
 	if err := c.LoadIssue(ctx); err != nil {
 		return err
 	}
@@ -110,7 +110,7 @@ func UpdateComment(ctx context.Context, c *issues_model.Comment, doer *user_mode
 		}
 	}
 
-	if err := issues_model.UpdateComment(ctx, c, doer); err != nil {
+	if err := issues_model.UpdateComment(ctx, c, contentVersion, doer); err != nil {
 		return err
 	}
 

services/issue/content.go

@@ -13,7 +13,7 @@ import (
 )
 
 // ChangeContent changes issue content, as the given user.
-func ChangeContent(ctx context.Context, issue *issues_model.Issue, doer *user_model.User, content string) error {
+func ChangeContent(ctx context.Context, issue *issues_model.Issue, doer *user_model.User, content string, contentVersion int) error {
 	if err := issue.LoadRepo(ctx); err != nil {
 		return err
 	}
@@ -26,7 +26,7 @@ func ChangeContent(ctx context.Context, issue *issues_model.Issue, doer *user_mo
 
 	oldContent := issue.Content
 
-	if err := issues_model.ChangeIssueContent(ctx, issue, doer, content); err != nil {
+	if err := issues_model.ChangeIssueContent(ctx, issue, doer, content, contentVersion); err != nil {
 		return err
 	}
 

templates/repo/diff/comments.tmpl

@@ -61,7 +61,7 @@
 			{{end}}
 			</div>
 			<div id="issuecomment-{{.ID}}-raw" class="raw-content tw-hidden">{{.Content}}</div>
-			<div class="edit-content-zone tw-hidden" data-update-url="{{$.root.RepoLink}}/comments/{{.ID}}" data-context="{{$.root.RepoLink}}" data-attachment-url="{{$.root.RepoLink}}/comments/{{.ID}}/attachments"></div>
+			<div class="edit-content-zone tw-hidden" data-update-url="{{$.root.RepoLink}}/comments/{{.ID}}" data-content-version="{{.ContentVersion}}" data-context="{{$.root.RepoLink}}" data-attachment-url="{{$.root.RepoLink}}/comments/{{.ID}}/attachments"></div>
 			{{if .Attachments}}
 				{{template "repo/issue/view_content/attachments" dict "Attachments" .Attachments "RenderedContent" .RenderedContent}}
 			{{end}}

templates/repo/issue/view_content.tmpl

@@ -60,7 +60,7 @@
 							{{end}}
 						</div>
 						<div id="issue-{{.Issue.ID}}-raw" class="raw-content tw-hidden">{{.Issue.Content}}</div>
-						<div class="edit-content-zone tw-hidden" data-update-url="{{$.RepoLink}}/issues/{{.Issue.Index}}/content" data-context="{{.RepoLink}}" data-attachment-url="{{$.RepoLink}}/issues/{{.Issue.Index}}/attachments" data-view-attachment-url="{{$.RepoLink}}/issues/{{.Issue.Index}}/view-attachments"></div>
+						<div class="edit-content-zone tw-hidden" data-update-url="{{$.RepoLink}}/issues/{{.Issue.Index}}/content" data-content-version="{{.Issue.ContentVersion}}" data-context="{{.RepoLink}}" data-attachment-url="{{$.RepoLink}}/issues/{{.Issue.Index}}/attachments" data-view-attachment-url="{{$.RepoLink}}/issues/{{.Issue.Index}}/view-attachments"></div>
 						{{if .Issue.Attachments}}
 							{{template "repo/issue/view_content/attachments" dict "Attachments" .Issue.Attachments "RenderedContent" .Issue.RenderedContent}}
 						{{end}}

templates/repo/issue/view_content/comments.tmpl

@@ -67,7 +67,7 @@
 							{{end}}
 						</div>
 						<div id="issuecomment-{{.ID}}-raw" class="raw-content tw-hidden">{{.Content}}</div>
-						<div class="edit-content-zone tw-hidden" data-update-url="{{$.RepoLink}}/comments/{{.ID}}" data-context="{{$.RepoLink}}" data-attachment-url="{{$.RepoLink}}/comments/{{.ID}}/attachments"></div>
+						<div class="edit-content-zone tw-hidden" data-update-url="{{$.RepoLink}}/comments/{{.ID}}" data-content-version="{{.ContentVersion}}" data-context="{{$.RepoLink}}" data-attachment-url="{{$.RepoLink}}/comments/{{.ID}}/attachments"></div>
 						{{if .Attachments}}
 							{{template "repo/issue/view_content/attachments" dict "Attachments" .Attachments "RenderedContent" .RenderedContent}}
 						{{end}}
@@ -441,7 +441,7 @@
 								{{end}}
 							</div>
 							<div id="issuecomment-{{.ID}}-raw" class="raw-content tw-hidden">{{.Content}}</div>
-							<div class="edit-content-zone tw-hidden" data-update-url="{{$.RepoLink}}/comments/{{.ID}}" data-context="{{$.RepoLink}}" data-attachment-url="{{$.RepoLink}}/comments/{{.ID}}/attachments"></div>
+							<div class="edit-content-zone tw-hidden" data-update-url="{{$.RepoLink}}/comments/{{.ID}}" data-content-version="{{.ContentVersion}}" data-context="{{$.RepoLink}}" data-attachment-url="{{$.RepoLink}}/comments/{{.ID}}/attachments"></div>
 							{{if .Attachments}}
 								{{template "repo/issue/view_content/attachments" dict "Attachments" .Attachments "RenderedContent" .RenderedContent}}
 							{{end}}

templates/repo/issue/view_content/conversation.tmpl

@@ -96,7 +96,7 @@
 								{{end}}
 								</div>
 								<div id="issuecomment-{{.ID}}-raw" class="raw-content tw-hidden">{{.Content}}</div>
-								<div class="edit-content-zone tw-hidden" data-update-url="{{$.RepoLink}}/comments/{{.ID}}" data-context="{{$.RepoLink}}" data-attachment-url="{{$.RepoLink}}/comments/{{.ID}}/attachments"></div>
+								<div class="edit-content-zone tw-hidden" data-update-url="{{$.RepoLink}}/comments/{{.ID}}" data-content-version="{{.ContentVersion}}" data-context="{{$.RepoLink}}" data-attachment-url="{{$.RepoLink}}/comments/{{.ID}}/attachments"></div>
 								{{if .Attachments}}
 									{{template "repo/issue/view_content/attachments" dict "Attachments" .Attachments "RenderedContent" .RenderedContent}}
 								{{end}}

tests/integration/issue_test.go

@@ -191,6 +191,34 @@ func TestNewIssue(t *testing.T) {
 	testNewIssue(t, session, "user2", "repo1", "Title", "Description")
 }
 
+func TestEditIssue(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+	session := loginUser(t, "user2")
+	issueURL := testNewIssue(t, session, "user2", "repo1", "Title", "Description")
+
+	req := NewRequestWithValues(t, "POST", fmt.Sprintf("%s/content", issueURL), map[string]string{
+		"_csrf":   GetCSRF(t, session, issueURL),
+		"content": "modified content",
+		"context": fmt.Sprintf("/%s/%s", "user2", "repo1"),
+	})
+	session.MakeRequest(t, req, http.StatusOK)
+
+	req = NewRequestWithValues(t, "POST", fmt.Sprintf("%s/content", issueURL), map[string]string{
+		"_csrf":   GetCSRF(t, session, issueURL),
+		"content": "modified content",
+		"context": fmt.Sprintf("/%s/%s", "user2", "repo1"),
+	})
+	session.MakeRequest(t, req, http.StatusBadRequest)
+
+	req = NewRequestWithValues(t, "POST", fmt.Sprintf("%s/content", issueURL), map[string]string{
+		"_csrf":           GetCSRF(t, session, issueURL),
+		"content":         "modified content",
+		"content_version": "1",
+		"context":         fmt.Sprintf("/%s/%s", "user2", "repo1"),
+	})
+	session.MakeRequest(t, req, http.StatusOK)
+}
+
 func TestIssueCommentClose(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()
 	session := loginUser(t, "user2")
@@ -257,6 +285,44 @@ func TestIssueCommentUpdate(t *testing.T) {
 	assert.Equal(t, modifiedContent, comment.Content)
 }
 
+func TestIssueCommentUpdateSimultaneously(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+	session := loginUser(t, "user2")
+	issueURL := testNewIssue(t, session, "user2", "repo1", "Title", "Description")
+	comment1 := "Test comment 1"
+	commentID := testIssueAddComment(t, session, issueURL, comment1, "")
+
+	comment := unittest.AssertExistsAndLoadBean(t, &issues_model.Comment{ID: commentID})
+	assert.Equal(t, comment1, comment.Content)
+
+	modifiedContent := comment.Content + "MODIFIED"
+
+	req := NewRequestWithValues(t, "POST", fmt.Sprintf("/%s/%s/comments/%d", "user2", "repo1", commentID), map[string]string{
+		"_csrf":   GetCSRF(t, session, issueURL),
+		"content": modifiedContent,
+	})
+	session.MakeRequest(t, req, http.StatusOK)
+
+	modifiedContent = comment.Content + "2"
+
+	req = NewRequestWithValues(t, "POST", fmt.Sprintf("/%s/%s/comments/%d", "user2", "repo1", commentID), map[string]string{
+		"_csrf":   GetCSRF(t, session, issueURL),
+		"content": modifiedContent,
+	})
+	session.MakeRequest(t, req, http.StatusBadRequest)
+
+	req = NewRequestWithValues(t, "POST", fmt.Sprintf("/%s/%s/comments/%d", "user2", "repo1", commentID), map[string]string{
+		"_csrf":           GetCSRF(t, session, issueURL),
+		"content":         modifiedContent,
+		"content_version": "1",
+	})
+	session.MakeRequest(t, req, http.StatusOK)
+
+	comment = unittest.AssertExistsAndLoadBean(t, &issues_model.Comment{ID: commentID})
+	assert.Equal(t, modifiedContent, comment.Content)
+	assert.Equal(t, 2, comment.ContentVersion)
+}
+
 func TestIssueReaction(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()
 	session := loginUser(t, "user2")

web_src/js/features/repo-issue-edit.js

@@ -3,6 +3,7 @@ import {handleReply} from './repo-issue.js';
 import {getComboMarkdownEditor, initComboMarkdownEditor} from './comp/ComboMarkdownEditor.js';
 import {createDropzone} from './dropzone.js';
 import {GET, POST} from '../modules/fetch.js';
+import {showErrorToast} from '../modules/toast.js';
 import {hideElem, showElem} from '../utils/dom.js';
 import {attachRefIssueContextPopup} from './contextpopup.js';
 import {initCommentContent, initMarkupContent} from '../markup/content.js';
@@ -124,11 +125,17 @@ async function onEditContent(event) {
       const params = new URLSearchParams({
         content: comboMarkdownEditor.value(),
         context: editContentZone.getAttribute('data-context'),
+        content_version: editContentZone.getAttribute('data-content-version'),
       });
       for (const fileInput of dropzoneInst?.element.querySelectorAll('.files [name=files]')) params.append('files[]', fileInput.value);
 
       const response = await POST(editContentZone.getAttribute('data-update-url'), {data: params});
       const data = await response.json();
+      if (response.status === 400) {
+        showErrorToast(data.errorMessage);
+        return;
+      }
+      editContentZone.setAttribute('data-content-version', data.contentVersion);
       if (!data.content) {
         renderContent.innerHTML = document.getElementById('no-content').innerHTML;
         rawContent.textContent = '';

web_src/js/markup/tasklist.js

@@ -1,4 +1,5 @@
 import {POST} from '../modules/fetch.js';
+import {showErrorToast} from '../modules/toast.js';
 
 const preventListener = (e) => e.preventDefault();
 
@@ -54,13 +55,20 @@ export function initMarkupTasklist() {
           const editContentZone = container.querySelector('.edit-content-zone');
           const updateUrl = editContentZone.getAttribute('data-update-url');
           const context = editContentZone.getAttribute('data-context');
+          const contentVersion = editContentZone.getAttribute('data-content-version');
 
           const requestBody = new FormData();
           requestBody.append('ignore_attachments', 'true');
           requestBody.append('content', newContent);
           requestBody.append('context', context);
-          await POST(updateUrl, {data: requestBody});
+          requestBody.append('content_version', contentVersion);
-
+          const response = await POST(updateUrl, {data: requestBody});
+          const data = await response.json();
+          if (response.status === 400) {
+            showErrorToast(data.errorMessage);
+            return;
+          }
+          editContentZone.setAttribute('data-content-version', data.contentVersion);
           rawContent.textContent = newContent;
         } catch (err) {
           checkbox.checked = !checkbox.checked;