Create TODO when MR became unmergeable

Old behavior of creating TODO when
“Merge When Pipeline Succeeds” service fails, is generalized to:

Create a TODO whenever MR became unmergeable
(and similar to notification, MR author and merge_user are both applicable)

6 files changed, 38 insertions, 53 deletions

diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 99687d305e7..a0ad7f3c609 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -127,6 +127,7 @@ class MergeRequest < ActiveRecord::Base
 
     after_transition unchecked: :cannot_be_merged do |merge_request, transition|
       NotificationService.new.merge_request_unmergeable(merge_request)
+      TodoService.new.merge_request_became_unmergeable(merge_request)
     end
 
     def check_state?(merge_status)
diff --git a/app/services/merge_requests/merge_when_pipeline_succeeds_service.rb b/app/services/merge_requests/merge_when_pipeline_succeeds_service.rb
index 850deb0ac7a..9a4e6eb2e88 100644
--- a/app/services/merge_requests/merge_when_pipeline_succeeds_service.rb
+++ b/app/services/merge_requests/merge_when_pipeline_succeeds_service.rb
@@ -24,11 +24,7 @@ module MergeRequests
 
       pipeline_merge_requests(pipeline) do |merge_request|
         next unless merge_request.merge_when_pipeline_succeeds?
-
-        unless merge_request.mergeable?
-          todo_service.merge_request_became_unmergeable(merge_request)
-          next
-        end
+        next unless merge_request.mergeable?
 
         merge_request.merge_async(merge_request.merge_user_id, merge_request.merge_params)
       end
diff --git a/app/services/todo_service.rb b/app/services/todo_service.rb
index ffd48e842c2..f91cd03bf5c 100644
--- a/app/services/todo_service.rb
+++ b/app/services/todo_service.rb
@@ -98,12 +98,12 @@ class TodoService
 
   # When a build fails on the HEAD of a merge request we should:
   #
-  #  * create a todo for author of MR to fix it
-  #  * create a todo for merge_user to keep an eye on it
+  #  * create a todo for each merge participant
   #
   def merge_request_build_failed(merge_request)
-    create_build_failed_todo(merge_request, merge_request.author)
-    create_build_failed_todo(merge_request, merge_request.merge_user) if merge_request.merge_when_pipeline_succeeds?
+    merge_request.merge_participants.each do |user|
+      create_build_failed_todo(merge_request, user)
+    end
   end
 
   # When a new commit is pushed to a merge request we should:
@@ -116,20 +116,22 @@ class TodoService
 
   # When a build is retried to a merge request we should:
   #
-  #  * mark all pending todos related to the merge request for the author as done
-  #  * mark all pending todos related to the merge request for the merge_user as done
+  #  * mark all pending todos related to the merge request as done for each merge participant
   #
   def merge_request_build_retried(merge_request)
-    mark_pending_todos_as_done(merge_request, merge_request.author)
-    mark_pending_todos_as_done(merge_request, merge_request.merge_user) if merge_request.merge_when_pipeline_succeeds?
+    merge_request.merge_participants.each do |user|
+      mark_pending_todos_as_done(merge_request, user)
+    end
   end
 
-  # When a merge request could not be automatically merged due to its unmergeable state we should:
+  # When a merge request could not be merged due to its unmergeable state we should:
   #
-  #  * create a todo for a merge_user
+  #  * create a todo for each merge participant
   #
   def merge_request_became_unmergeable(merge_request)
-    create_unmergeable_todo(merge_request, merge_request.merge_user) if merge_request.merge_when_pipeline_succeeds?
+    merge_request.merge_participants.each do |user|
+      create_unmergeable_todo(merge_request, user)
+    end
   end
 
   # When create a note we should:
@@ -275,9 +277,9 @@ class TodoService
     create_todos(todo_author, attributes)
   end
 
-  def create_unmergeable_todo(merge_request, merge_user)
-    attributes = attributes_for_todo(merge_request.project, merge_request, merge_user, Todo::UNMERGEABLE)
-    create_todos(merge_user, attributes)
+  def create_unmergeable_todo(merge_request, todo_author)
+    attributes = attributes_for_todo(merge_request.project, merge_request, todo_author, Todo::UNMERGEABLE)
+    create_todos(todo_author, attributes)
   end
 
   def attributes_for_target(target)
diff --git a/doc/workflow/todos.md b/doc/workflow/todos.md
index f13d29884d4..762bf616268 100644
--- a/doc/workflow/todos.md
+++ b/doc/workflow/todos.md
@@ -31,6 +31,9 @@ A Todo appears in your Todos dashboard when:
 - you are `@mentioned` in a comment on a commit,
 - a job in the CI pipeline running for your merge request failed, but this
   job is not allowed to fail.
+- a merge request becomes unmergeable, and you are either:
+  - the author, or
+  - have set it to automatically merge once pipeline succeeds.
 
 ### Directly addressed Todos
 
diff --git a/spec/services/merge_requests/merge_when_pipeline_succeeds_service_spec.rb b/spec/services/merge_requests/merge_when_pipeline_succeeds_service_spec.rb
index 240aa638f79..8838742a637 100644
--- a/spec/services/merge_requests/merge_when_pipeline_succeeds_service_spec.rb
+++ b/spec/services/merge_requests/merge_when_pipeline_succeeds_service_spec.rb
@@ -112,32 +112,6 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
         service.trigger(unrelated_pipeline)
       end
     end
-
-    context 'when the merge request is not mergeable' do
-      let(:mr_conflict) do
-        create(:merge_request, merge_when_pipeline_succeeds: true, merge_user: user,
-                               source_branch: 'master', target_branch: 'feature-conflict',
-                               source_project: project, target_project: project)
-      end
-
-      let(:conflict_pipeline) do
-        create(:ci_pipeline, project: project, ref: mr_conflict.source_branch,
-                             sha: mr_conflict.diff_head_sha, status: 'success',
-                             head_pipeline_of: mr_conflict)
-      end
-
-      it 'does not merge the merge request' do
-        expect(MergeWorker).not_to receive(:perform_async)
-
-        service.trigger(conflict_pipeline)
-      end
-
-      it 'creates todos for unmergeability' do
-        expect_any_instance_of(TodoService).to receive(:merge_request_became_unmergeable).with(mr_conflict)
-
-        service.trigger(conflict_pipeline)
-      end
-    end
   end
 
   describe "#cancel" do
diff --git a/spec/services/todo_service_spec.rb b/spec/services/todo_service_spec.rb
index 562b89e6767..9a51c873b30 100644
--- a/spec/services/todo_service_spec.rb
+++ b/spec/services/todo_service_spec.rb
@@ -721,17 +721,18 @@ describe TodoService do
     end
 
     describe '#merge_request_build_failed' do
-      it 'creates a pending todo for the merge request author' do
-        service.merge_request_build_failed(mr_unassigned)
+      let(:merge_participants) { [mr_unassigned.author, admin] }
 
-        should_create_todo(user: author, target: mr_unassigned, action: Todo::BUILD_FAILED)
+      before do
+        allow(mr_unassigned).to receive(:merge_participants).and_return(merge_participants)
       end
 
-      it 'creates a pending todo for merge_user' do
-        mr_unassigned.update(merge_when_pipeline_succeeds: true, merge_user: admin)
+      it 'creates a pending todo for each merge_participant' do
         service.merge_request_build_failed(mr_unassigned)
 
-        should_create_todo(user: admin, author: admin, target: mr_unassigned, action: Todo::BUILD_FAILED)
+        merge_participants.each do |participant|
+          should_create_todo(user: participant, author: participant, target: mr_unassigned, action: Todo::BUILD_FAILED)
+        end
       end
     end
 
@@ -747,11 +748,19 @@ describe TodoService do
     end
 
     describe '#merge_request_became_unmergeable' do
-      it 'creates a pending todo for a merge_user' do
+      let(:merge_participants) { [admin, create(:user)] }
+
+      before do
+        allow(mr_unassigned).to receive(:merge_participants).and_return(merge_participants)
+      end
+
+      it 'creates a pending todo for each merge_participant' do
         mr_unassigned.update(merge_when_pipeline_succeeds: true, merge_user: admin)
         service.merge_request_became_unmergeable(mr_unassigned)
 
-        should_create_todo(user: admin, author: admin, target: mr_unassigned, action: Todo::UNMERGEABLE)
+        merge_participants.each do |participant|
+          should_create_todo(user: participant, author: participant, target: mr_unassigned, action: Todo::UNMERGEABLE)
+        end
       end
     end