Enable multiline_comments by default

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39370

app/controllers/projects/merge_requests_controller.rb

@@ -33,7 +33,7 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
     push_frontend_feature_flag(:widget_visibility_polling, @project, default_enabled: true)
     push_frontend_feature_flag(:merge_ref_head_comments, @project, default_enabled: true)
     push_frontend_feature_flag(:mr_commit_neighbor_nav, @project, default_enabled: true)
-    push_frontend_feature_flag(:multiline_comments, @project)
+    push_frontend_feature_flag(:multiline_comments, @project, default_enabled: true)
     push_frontend_feature_flag(:file_identifier_hash)
     push_frontend_feature_flag(:batch_suggestions, @project, default_enabled: true)
     push_frontend_feature_flag(:auto_expand_collapsed_diffs, @project, default_enabled: true)

changelogs/unreleased/jdb-mlc-enable-default.yml

+---
+title: Enable Multiline Comments by default
+merge_request: 39370
+author:
+type: changed

doc/user/project/merge_requests/reviewing_and_managing_merge_requests.md

@@ -151,11 +151,12 @@ in a Merge Request. To do so, click the **{comment}** **comment** icon in the gu
 ### Commenting on multiple lines
 
 > - [Introduced](https://gitlab.com/gitlab-org/ux-research/-/issues/870) in GitLab 13.2.
-> - It's deployed behind a feature flag, disabled by default.
+> - It's deployed behind a feature flag, enabled by default.
+> - [Became enabled by default](https://gitlab.com/gitlab-org/gitlab/-/issues/221268) on GitLab 13.3.
 > - It's enabled on GitLab.com.
-> - It can be enabled or disabled per-project.
+> - It can be disabled or enabled per-project.
 > - It's recommended for production use.
-> - For GitLab self-managed instances, GitLab administrators can opt to [enable it](#enable-or-disable-multiline-comments-core-only). **(CORE ONLY)**
+> - For GitLab self-managed instances, GitLab administrators can opt to [disable it](#enable-or-disable-multiline-comments-core-only). **(CORE ONLY)**
 
 GitLab provides a way to select which lines of code a comment refers to. After starting a comment
 a dropdown selector is shown to select the first line that this comment refers to.
@@ -178,16 +179,16 @@ It is deployed behind a feature flag that is **disabled by default**.
 [GitLab administrators with access to the GitLab Rails console](../../../administration/feature_flags.md)
 can opt to enable it for your instance.
 
-To enable it:
+To disable it:
 
 ```ruby
-Feature.enable(:multiline_comments)
+Feature.disable(:multiline_comments)
 ```
 
-To disable it:
+To enable it:
 
 ```ruby
-Feature.disable(:multiline_comments)
+Feature.enable(:multiline_comments)
 ```
 
 ## Pipeline status in merge requests widgets