Merge branch '19035-fix-merge-issue' into 'master'

Fix a wrong MR status when merge_when_build_succeeds & project.only_allow_merge_if_build_succeeds are true

## What does this MR do?

Fix a wrong MR status when merge_when_build_succeeds & project.only_allow_merge_if_build_succeeds are true.

## Are there points in the code the reviewer needs to double check?

@stanhu I reused your proposal from the issue, I think it's a good enough solution.

## What are the relevant issue numbers?

Fixes #19035.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4912

CHANGELOG

@@ -39,6 +39,8 @@ v 8.9.1 (unreleased)
   - Fix pagination when sorting by columns with lots of ties (like priority)
   - Implement Subresource Integrity for CSS and JavaScript assets. This prevents malicious assets from loading in the case of a CDN compromise.
   - Fix user creation with stronger minimum password requirements !4054 (nathan-pmt)
+  - Add API endpoint for a group issues !4520 (mahcsig)
+  - Fix a wrong MR status when merge_when_build_succeeds & project.only_allow_merge_if_build_succeeds are true. !4912
 
 v 8.9.0
   - Fix builds API response not including commit data

app/controllers/projects/merge_requests_controller.rb

@@ -199,7 +199,9 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   def merge
     return access_denied! unless @merge_request.can_be_merged_by?(current_user)
 
-    unless @merge_request.mergeable?
+    # Disable the CI check if merge_when_build_succeeds is enabled since we have
+    # to wait until CI completes to know
+    unless @merge_request.mergeable?(skip_ci_check: merge_when_build_succeeds_active?)
       @status = :failed
       return
     end
@@ -381,4 +383,9 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   def ensure_ref_fetched
     @merge_request.ensure_ref_fetched
   end
+
+  def merge_when_build_succeeds_active?
+    params[:merge_when_build_succeeds].present? &&
+      @merge_request.pipeline && @merge_request.pipeline.active?
+  end
 end

app/models/merge_request.rb

@@ -264,19 +264,19 @@ class MergeRequest < ActiveRecord::Base
     self.title.sub(WIP_REGEX, "")
   end
 
-  def mergeable?
-    return false unless mergeable_state?
+  def mergeable?(skip_ci_check: false)
+    return false unless mergeable_state?(skip_ci_check: skip_ci_check)
 
     check_if_can_be_merged
 
     can_be_merged?
   end
 
-  def mergeable_state?
+  def mergeable_state?(skip_ci_check: false)
     return false unless open?
     return false if work_in_progress?
     return false if broken?
-    return false unless mergeable_ci_state?
+    return false unless skip_ci_check || mergeable_ci_state?
 
     true
   end

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -264,6 +264,18 @@ describe Projects::MergeRequestsController do
 
           merge_when_build_succeeds
         end
+
+        context 'when project.only_allow_merge_if_build_succeeds? is true' do
+          before do
+            project.update_column(:only_allow_merge_if_build_succeeds, true)
+          end
+
+          it 'returns :merge_when_build_succeeds' do
+            merge_when_build_succeeds
+
+            expect(assigns(:status)).to eq(:merge_when_build_succeeds)
+          end
+        end
       end
     end
   end