7 files changed, 32 insertions, 7 deletions
diff --git a/app/controllers/concerns/issuable_actions.rb b/app/controllers/concerns/issuable_actions.rb
index cd3fa641e89..05d88429cfe 100644
--- a/app/controllers/concerns/issuable_actions.rb
+++ b/app/controllers/concerns/issuable_actions.rb
@@ -8,7 +8,7 @@ module IssuableActions
     before_action :authorize_destroy_issuable!, only: :destroy
     before_action :authorize_admin_issuable!, only: :bulk_update
     before_action only: :show do
-      push_frontend_feature_flag(:reply_to_individual_notes)
+      push_frontend_feature_flag(:reply_to_individual_notes, default_enabled: true)
     end
   end
 
diff --git a/app/models/individual_note_discussion.rb b/app/models/individual_note_discussion.rb
index b4a661ae5b4..3b6b68a9c5f 100644
--- a/app/models/individual_note_discussion.rb
+++ b/app/models/individual_note_discussion.rb
@@ -14,7 +14,7 @@ class IndividualNoteDiscussion < Discussion
   end
 
   def can_convert_to_discussion?
-    noteable.supports_replying_to_individual_notes? && Feature.enabled?(:reply_to_individual_notes)
+    noteable.supports_replying_to_individual_notes? && Feature.enabled?(:reply_to_individual_notes, default_enabled: true)
   end
 
   def convert_to_discussion!(save: false)
diff --git a/changelogs/unreleased/winh-enable-reply_to_individual_notes.yml b/changelogs/unreleased/winh-enable-reply_to_individual_notes.yml
new file mode 100644
index 00000000000..a9c280320dc
--- /dev/null
+++ b/changelogs/unreleased/winh-enable-reply_to_individual_notes.yml
@@ -0,0 +1,5 @@
+---
+title: Add button to start discussion from single comment
+merge_request: 25575
+author:
+type: added
diff --git a/doc/user/discussions/img/reply_to_comment.gif b/doc/user/discussions/img/reply_to_comment.gif
new file mode 100644
index 00000000000..c62f7fdb5fe
--- /dev/null
+++ b/doc/user/discussions/img/reply_to_comment.gif
diff --git a/doc/user/discussions/img/reply_to_comment_button.png b/doc/user/discussions/img/reply_to_comment_button.png
new file mode 100644
index 00000000000..d362b19785c
--- /dev/null
+++ b/doc/user/discussions/img/reply_to_comment_button.png
diff --git a/doc/user/discussions/index.md b/doc/user/discussions/index.md
index 1e2fad1efe9..02bfd2bec7a 100644
--- a/doc/user/discussions/index.md
+++ b/doc/user/discussions/index.md
@@ -10,8 +10,9 @@ You can leave a comment in the following places:
 - commits
 - commit diffs
 
-The comment area supports [Markdown] and [quick actions]. One can edit their
-own comment at any time, and anyone with [Maintainer access level][permissions] or
+The comment area supports [Markdown] and [quick actions]. Every individual
+comment can be [turned into a discussion](#start-a-discussion-by-replying-to-a-non-discussion-comment)
+One can also edit their own comment at any time, and anyone with [Maintainer access level][permissions] or
 higher can also edit a comment made by someone else.
 
 You could also reply to the notification email in order to reply to a comment,
@@ -339,6 +340,26 @@ and push the suggested change directly into the codebase in the merge request's
 Custom commit messages will be introduced by
 [#54404](https://gitlab.com/gitlab-org/gitlab-ce/issues/54404).
 
+## Start a discussion by replying to a non-discussion comment
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/30299) in GitLab 11.9
+
+To reply a non-discussion comment, you can use the **Reply to comment** button.
+
+![Reply to comment button](img/reply_to_comment_button.png)
+
+The **Reply to comment** button is only displayed if you have permissions to reply to an existing discussion, or start a discussion from a standalone comment.
+
+Clicking on the **Reply to comment** button will bring the reply area into focus and you can type your reply.
+
+![Reply to comment feature](img/reply_to_comment.gif)
+
+Relying to a non-discussion comment will convert the non-discussion comment to a 
+threaded discussion once the reply is submitted. This conversion is considered an edit
+to the original comment, so a note about when it was last edited will appear underneath it.
+
+This feature only exists for Issues, Merge requests, and Epics. Commits, Snippets and Merge request diff discussions are not supported yet.
+
 [ce-5022]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5022
 [ce-7125]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7125
 [ce-7527]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7527
diff --git a/spec/features/merge_request/user_posts_notes_spec.rb b/spec/features/merge_request/user_posts_notes_spec.rb
index 1bbcf455ac7..dc0862be6fc 100644
--- a/spec/features/merge_request/user_posts_notes_spec.rb
+++ b/spec/features/merge_request/user_posts_notes_spec.rb
@@ -67,7 +67,7 @@ describe 'Merge request > User posts notes', :js do
       end
     end
 
-    describe 'when reply_to_individual_notes feature flag is not set' do
+    describe 'when reply_to_individual_notes feature flag is disabled' do
       before do
         stub_feature_flags(reply_to_individual_notes: false)
         visit project_merge_request_path(project, merge_request)
@@ -78,9 +78,8 @@ describe 'Merge request > User posts notes', :js do
       end
     end
 
-    describe 'when reply_to_individual_notes feature flag is set' do
+    describe 'when reply_to_individual_notes feature flag is not set' do
       before do
-        stub_feature_flags(reply_to_individual_notes: true)
         visit project_merge_request_path(project, merge_request)
       end