[#28991] Wiki page edit button only appears on the current commit page

app/models/wiki_page.rb

@@ -149,6 +149,12 @@ class WikiPage
   end
 
   # Returns boolean True or False if this instance
+  # is the latest commit version of the page.
+  def latest?
+    !historical?
+  end
+
+  # Returns boolean True or False if this instance
   # has been fully saved to disk or not.
   def persisted?
     @persisted == true

app/views/projects/wikis/_main_links.html.haml

@@ -4,6 +4,6 @@
       New Page
   = link_to namespace_project_wiki_history_path(@project.namespace, @project, @page), class: "btn" do
     Page History
-  - if can?(current_user, :create_wiki, @project)
+  - if can?(current_user, :create_wiki, @project) && @page.latest?
     = link_to namespace_project_wiki_edit_path(@project.namespace, @project, @page), class: "btn" do
       Edit

changelogs/unreleased/28991-viewing-old-wiki-page-version-edit-button-exists.yml

+---
+title: When viewing old wiki page version, edit button should be disabled
+merge_request: 9966 
+author: TM Lee

spec/features/projects/wiki/user_views_project_wiki_page_spec.rb

+require 'spec_helper'
+
+feature 'Projects > Wiki > User views the wiki page', feature: true do
+  let(:user) { create(:user) }
+  let(:project) { create(:project, :public) }
+  let(:old_page_version_id) { wiki_page.versions.last.id }
+  let(:wiki_page) do
+    WikiPages::CreateService.new(
+      project,
+      user,
+      title: 'home',
+      content: '[some link](other-page)'
+    ).execute
+  end
+
+  background do
+    project.team << [user, :master]
+    login_as(user)
+    WikiPages::UpdateService.new(
+      project,
+      user,
+      message: 'updated home',
+      content: 'updated [some link](other-page)',
+      format: :markdown
+    ).execute(wiki_page)
+  end
+
+  scenario 'Visit Wiki Page Current Commit' do
+    visit namespace_project_wiki_path(project.namespace, project, wiki_page)
+
+    expect(page).to have_selector('a.btn', text: 'Edit')
+  end
+
+  scenario 'Visit Wiki Page Historical Commit' do
+    visit namespace_project_wiki_path(
+      project.namespace,
+      project,
+      wiki_page,
+      version_id: old_page_version_id
+    )
+
+    expect(page).not_to have_selector('a.btn', text: 'Edit')
+  end
+end