FEATURE: Allow admins to permanently delete revisions (#19913)

# Context
This PR introduces the ability to permanently delete revisions from a post while maintaining the changes implemented by the revisions.
Additional Context: /t/90301

# Functionality
In the case a staff member wants to _remove the visual cue_ that a post has been edited eg.

<img width="86" alt="Screenshot 2023-01-18 at 2 59 12 PM" src="https://user-images.githubusercontent.com/50783505/213293333-9c881229-ab18-4591-b39b-e3419a67907d.png">

while maintaining the changes made in the edits, they can enable the (hidden) site setting of `can_permanently_delete`.
When this is enabled, after _hiding_ the revisions

<img width="149" alt="Screenshot 2023-01-19 at 1 53 35 PM" src="https://user-images.githubusercontent.com/50783505/213546080-2a9e9c55-b3ef-428e-a93d-1b6ba287dfae.png">

there will be an additional button in the history modal to <kbd>Delete revisions</kbd> on a post.

<img width="997" alt="Screenshot 2023-01-19 at 1 49 51 PM" src="https://user-images.githubusercontent.com/50783505/213546333-49042558-50ab-4724-9da7-08bacc68d38d.png">

Since this action is permanent, we display a confirmation dialog prior to triggering the destroy call

<img width="722" alt="Screenshot 2023-01-19 at 1 55 59 PM" src="https://user-images.githubusercontent.com/50783505/213546487-96ea6e89-ac49-4892-b4b0-28996e3c867f.png">

Once confirmed the history modal will close and the post will `rebake` to display an _unedited_ post.

<img width="868" alt="Screenshot 2023-01-19 at 1 56 35 PM" src="https://user-images.githubusercontent.com/50783505/213546608-d6436717-8484-4132-a1a8-b7a348d92728.png">
 
see that there is not a visual que for _revision have been made on this post_ for a post that **HAS** been edited. In addition to this, a user history log for `purge_post_revisions` will be added for each action completed.

# Limits
- Admins are rate limited to 20 posts per minute

app/assets/javascripts/discourse/app/controllers/history.js

@@ -114,6 +114,17 @@ export default Controller.extend(ModalFunctionality, {
     );
   },
 
+  permanentlyDeleteRevisions(postId) {
+    this.dialog.yesNoConfirm({
+      message: I18n.t("post.revisions.controls.destroy_confirm"),
+      didConfirm: () => {
+        Post.permanentlyDeleteRevisions(postId).then(() => {
+          this.send("closeModal");
+        });
+      },
+    });
+  },
+
   show(postId, postVersion) {
     Post.showRevision(postId, postVersion).then(() =>
       this.refresh(postId, postVersion)
@@ -162,6 +173,7 @@ export default Controller.extend(ModalFunctionality, {
   },
 
   displayRevisions: gt("model.version_count", 2),
+
   displayGoToFirst: propertyGreaterThan(
     "model.current_revision",
     "model.first_revision"
@@ -215,6 +227,15 @@ export default Controller.extend(ModalFunctionality, {
     return this.currentUser && this.currentUser.get("staff");
   },
 
+  @discourseComputed("model.previous_hidden")
+  displayPermanentlyDeleteButton(previousHidden) {
+    return (
+      this.siteSettings.can_permanently_delete &&
+      this.currentUser?.staff &&
+      previousHidden
+    );
+  },
+
   isEitherRevisionHidden: or("model.previous_hidden", "model.current_hidden"),
 
   @discourseComputed(
@@ -352,6 +373,9 @@ export default Controller.extend(ModalFunctionality, {
     hideVersion() {
       this.hide(this.get("model.post_id"), this.get("model.current_revision"));
     },
+    permanentlyDeleteVersions() {
+      this.permanentlyDeleteRevisions(this.get("model.post_id"));
+    },
     showVersion() {
       this.show(this.get("model.post_id"), this.get("model.current_revision"));
     },

app/assets/javascripts/discourse/app/models/post.js

@@ -461,6 +461,12 @@ Post.reopenClass({
     });
   },
 
+  permanentlyDeleteRevisions(postId) {
+    return ajax(`/posts/${postId}/revisions/permanently_delete`, {
+      type: "DELETE",
+    });
+  },
+
   showRevision(postId, version) {
     return ajax(`/posts/${postId}/revisions/${version}/show`, {
       type: "PUT",

app/assets/javascripts/discourse/app/templates/modal/history.hbs

@@ -250,6 +250,16 @@
           @disabled={{this.loading}}
         />
       {{/if}}
+
+      {{#if this.displayPermanentlyDeleteButton}}
+        <DButton
+          @action={{action "permanentlyDeleteVersions"}}
+          @icon="far-trash-alt"
+          @label="post.revisions.controls.destroy"
+          @class="btn-danger"
+          @disabled={{this.loading}}
+        />
+      {{/if}}
     </div>
   </div>
 {{/if}}

app/controllers/posts_controller.rb

@@ -466,6 +466,33 @@ class PostsController < ApplicationController
     render body: nil
   end
 
+  def permanently_delete_revisions
+    guardian.ensure_can_permanently_delete_post_revisions!
+
+    post = find_post_from_params
+    raise Discourse::InvalidParameters.new(:post) if post.blank?
+    raise Discourse::NotFound unless post.revisions.present?
+
+    RateLimiter.new(
+      current_user,
+      "admin_permanently_delete_post_revisions",
+      20,
+      1.minute,
+      apply_limit_to_staff: true,
+    ).performed!
+
+    ActiveRecord::Base.transaction do
+      updated_at = Time.zone.now
+      post.revisions.destroy_all
+      post.update(version: 1, public_version: 1, last_version_at: updated_at)
+      StaffActionLogger.new(current_user).log_permanently_delete_post_revisions(post)
+    end
+
+    post.rebake!
+
+    render body: nil
+  end
+
   def show_revision
     post_revision = find_post_revision_from_params
     guardian.ensure_can_show_post_revision!(post_revision)

app/models/user_history.rb

@@ -119,6 +119,7 @@ class UserHistory < ActiveRecord::Base
         watched_word_create: 97,
         watched_word_destroy: 98,
         delete_group: 99,
+        permanently_delete_post_revisions: 100,
       )
   end
 
@@ -213,6 +214,7 @@ class UserHistory < ActiveRecord::Base
       watched_word_create
       watched_word_destroy
       delete_group
+      permanently_delete_post_revisions
     ]
   end
 

app/services/staff_action_logger.rb

@@ -954,6 +954,16 @@ class StaffActionLogger
     )
   end
 
+  def log_permanently_delete_post_revisions(post)
+    raise Discourse::InvalidParameters.new(:post) if post.nil?
+
+    UserHistory.create!(
+      action: UserHistory.actions[:permanently_delete_post_revisions],
+      acting_user_id: @admin.id,
+      post_id: post.id,
+    )
+  end
+
   private
 
   def get_changes(changes)

config/locales/client.en.yml

@@ -1121,7 +1121,7 @@ en:
         perm_denied_expl: "You denied permission for notifications. Allow notifications via your browser settings."
         disable: "Disable Notifications"
         enable: "Enable Notifications"
-        each_browser_note: 'Note: You have to change this setting on every browser you use. All notifications will be disabled if you pause notifications from user menu, regardless of this setting.'
+        each_browser_note: "Note: You have to change this setting on every browser you use. All notifications will be disabled if you pause notifications from user menu, regardless of this setting."
         consent_prompt: "Do you want live notifications when people reply to your posts?"
       dismiss: "Dismiss"
       dismiss_notifications: "Dismiss All"
@@ -3548,6 +3548,8 @@ en:
           last: "Last revision"
           hide: "Hide revision"
           show: "Show revision"
+          destroy: "Delete revisions"
+          destroy_confirm: "Are you sure you want to delete all of the revisions on this post? This action is permanent."
           revert: "Revert to revision %{revision}"
           edit_wiki: "Edit Wiki"
           edit_post: "Edit Post"

config/routes.rb

@@ -1082,6 +1082,7 @@ Discourse::Application.routes.draw do
       put "revisions/:revision/hide" => "posts#hide_revision", :constraints => { revision: /\d+/ }
       put "revisions/:revision/show" => "posts#show_revision", :constraints => { revision: /\d+/ }
       put "revisions/:revision/revert" => "posts#revert", :constraints => { revision: /\d+/ }
+      delete "revisions/permanently_delete" => "posts#permanently_delete_revisions"
       put "recover"
       collection do
         delete "destroy_many"

lib/guardian/post_revision_guardian.rb

@@ -13,6 +13,10 @@ module PostRevisionGuardian
     is_staff?
   end
 
+  def can_permanently_delete_post_revisions?
+    is_staff? && SiteSetting.can_permanently_delete
+  end
+
   def can_show_post_revision?(post_revision)
     is_staff?
   end

spec/requests/posts_controller_spec.rb

@@ -2049,6 +2049,76 @@ RSpec.describe PostsController do
     end
   end
 
+  describe "#permanently_delete_revisions" do
+    before { SiteSetting.can_permanently_delete = true }
+
+    fab!(:post) do
+      Fabricate(
+        :post,
+        user: Fabricate(:user),
+        raw: "Lorem ipsum dolor sit amet, cu nam libris tractatos, ancillae senserit ius ex",
+      )
+    end
+
+    fab!(:post_with_no_revisions) do
+      Fabricate(
+        :post,
+        user: Fabricate(:user),
+        raw: "Lorem ipsum dolor sit amet, cu nam libris tractatos, ancillae senserit ius ex",
+      )
+    end
+
+    fab!(:post_revision) { Fabricate(:post_revision, post: post) }
+    fab!(:post_revision_2) { Fabricate(:post_revision, post: post) }
+
+    let(:post_id) { post.id }
+
+    describe "when logged in as a regular user" do
+      it "does not delete revisions" do
+        sign_in(user)
+        delete "/posts/#{post_id}/revisions/permanently_delete.json"
+        expect(response).to_not be_successful
+      end
+    end
+
+    describe "when logged in as staff" do
+      before { sign_in(admin) }
+
+      it "fails when post record is not found" do
+        delete "/posts/#{post_id + 1}/revisions/permanently_delete.json"
+        expect(response).to_not be_successful
+      end
+
+      it "fails when no post revisions are found" do
+        delete "/posts/#{post_with_no_revisions.id}/revisions/permanently_delete.json"
+        expect(response).to_not be_successful
+      end
+
+      it "fails when 'can_permanently_delete' setting is false" do
+        SiteSetting.can_permanently_delete = false
+        delete "/posts/#{post_id}/revisions/permanently_delete.json"
+        expect(response).to_not be_successful
+      end
+
+      it "permanently deletes revisions from post and adds a staff log" do
+        delete "/posts/#{post_id}/revisions/permanently_delete.json"
+        expect(response.status).to eq(200)
+
+        # It creates a staff log
+        logs =
+          UserHistory.find_by(
+            action: UserHistory.actions[:permanently_delete_post_revisions],
+            acting_user_id: admin.id,
+            post_id: post_id,
+          )
+        expect(logs).to be_present
+
+        # ensure post revisions are deleted
+        expect(PostRevision.where(post: post)).to eq([])
+      end
+    end
+  end
+
   describe "#revert" do
     include_examples "action requires login", :put, "/posts/123/revisions/2/revert.json"