FIX: Don't advance draft sequence when editing topic title (#16002)

This commit handles the edge case where a draft is lost with no warnings if the user edits the title (or category/tags) of a topic while they're replying.to the same topic. Repro steps are as follows:

1. Start replying to a topic and type enough to get a draft saved.
2. Scroll up to the topic title and click the pencil icon next to the topic title, change the title, category and/or tags, and then save the changes.
3. Reload the page and you'll see that the draft is gone.

This happens because we only allow 1 draft per topic per user and when you edit the title of a topic that you're replying to, from the server perspective it'll look like as if you've submitted your reply so it will advance the draft sequence for the topic and delete the draft.

The fix in this commit makes `PostRevisor` skip advancing the draft sequence when a topic's title is edited using the pencil button next to the title.

Internal ticket: t60854.

Co-authored-by: Robin Ward <robin.ward@gmail.com>

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

@@ -980,7 +980,7 @@ export default Controller.extend(bufferedProperty("model"), {
       // save the modifications
       const props = this.get("buffered.buffer");
 
-      Topic.update(this.model, props)
+      Topic.update(this.model, props, { fastEdit: true })
         .then(() => {
           // We roll back on success here because `update` saves the properties to the topic
           this.rollbackBuffer();

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

@@ -661,7 +661,7 @@ Topic.reopenClass({
     }
   },
 
-  update(topic, props) {
+  update(topic, props, opts = {}) {
     // We support `category_id` and `categoryId` for compatibility
     if (typeof props.categoryId !== "undefined") {
       props.category_id = props.categoryId;
@@ -673,9 +673,13 @@ Topic.reopenClass({
       delete props.category_id;
     }
 
+    const data = { ...props };
+    if (opts.fastEdit) {
+      data.keep_existing_draft = true;
+    }
     return ajax(topic.get("url"), {
       type: "PUT",
-      data: JSON.stringify(props),
+      data: JSON.stringify(data),
       contentType: "application/json",
     }).then((result) => {
       // The title can be cleaned up server side

app/controllers/topics_controller.rb

@@ -397,7 +397,13 @@ class TopicsController < ApplicationController
       bypass_bump = should_bypass_bump?(changes)
 
       first_post = topic.ordered_posts.first
-      success = PostRevisor.new(first_post, topic).revise!(current_user, changes, validate_post: false, bypass_bump: bypass_bump)
+      success = PostRevisor.new(first_post, topic).revise!(
+        current_user,
+        changes,
+        validate_post: false,
+        bypass_bump: bypass_bump,
+        keep_existing_draft: params[:keep_existing_draft].to_s == "true"
+      )
 
       if !success && topic.errors.blank?
         topic.errors.add(:base, :unable_to_update)

lib/post_revisor.rb

@@ -159,7 +159,16 @@ class PostRevisor
       end
     end
 
-    return false unless should_revise?
+    if !should_revise?
+      # the draft sequence is advanced here to handle the edge case where a
+      # user opens the composer to edit a post and makes some changes (which
+      # saves a draft), but then un-does the changes and clicks save. In this
+      # case, should_revise? returns false because nothing has really changed
+      # in the post, but we want to get rid of the draft so we advance the
+      # sequence.
+      advance_draft_sequence if !opts[:keep_existing_draft]
+      return false
+    end
 
     @post.acting_user = @editor
     @topic.acting_user = @editor
@@ -204,7 +213,7 @@ class PostRevisor
       plugin_callbacks
 
       revise_topic
-      advance_draft_sequence
+      advance_draft_sequence if !opts[:keep_existing_draft]
     end
 
     # Lock the post by default if the appropriate setting is true
@@ -271,7 +280,6 @@ class PostRevisor
         return true
       end
     end
-    advance_draft_sequence
     false
   end
 

spec/lib/post_revisor_spec.rb

@@ -1236,6 +1236,33 @@ describe PostRevisor do
         end
       end
     end
+
+    context 'with drafts' do
+      it "does not advance draft sequence if keep_existing_draft option is true" do
+        post = Fabricate(:post, user: user)
+        topic = post.topic
+        draft_key = "topic_#{topic.id}"
+        data = { reply: "test 12222" }.to_json
+        Draft.set(user, draft_key, 0, data)
+        Draft.set(user, draft_key, 0, data)
+        expect {
+          PostRevisor.new(post).revise!(
+            post.user,
+            { title: "updated title for my topic" },
+            keep_existing_draft: true
+          )
+        }.to change { Draft.where(user: user, draft_key: draft_key).first.sequence }.by(0)
+          .and change { DraftSequence.where(user_id: user.id, draft_key: draft_key).first.sequence }.by(0)
+
+        expect {
+          PostRevisor.new(post).revise!(
+            post.user,
+            { title: "updated title for my topic" },
+          )
+        }.to change { Draft.where(user: user, draft_key: draft_key).count }.from(1).to(0)
+          .and change { DraftSequence.where(user_id: user.id, draft_key: draft_key).first.sequence }.by(1)
+      end
+    end
   end
 
   context 'when the review_every_post setting is enabled' do