Create a todo on failing MR build

When a build fails for a commit, create a todo for the author of the
merge request that commit is the HEAD of. If the commit isn't the HEAD
commit of any MR, don't do anything. If there already is a todo for that
user and MR, don't do anything.

Current limitations:
- This isn't configurable by project.
- The author of a merge request might not be the person who pushed the
  breaking commit.

5 files changed, 80 insertions, 22 deletions

diff --git a/app/services/merge_requests/add_todo_when_build_fails_service.rb b/app/services/merge_requests/add_todo_when_build_fails_service.rb
new file mode 100644
index 00000000000..566049525cb
--- /dev/null
+++ b/app/services/merge_requests/add_todo_when_build_fails_service.rb
@@ -0,0 +1,17 @@
+module MergeRequests
+  class AddTodoWhenBuildFailsService < MergeRequests::BaseService
+    # Adds a todo to the parent merge_request when a CI build fails
+    def execute(commit_status)
+      each_merge_request(commit_status) do |merge_request|
+        todo_service.merge_request_build_failed(merge_request)
+      end
+    end
+
+    # Closes any pending build failed todos for the parent MRs when a build is retried
+    def close(commit_status)
+      each_merge_request(commit_status) do |merge_request|
+        todo_service.merge_request_build_retried(merge_request)
+      end
+    end
+  end
+end
diff --git a/app/services/merge_requests/base_service.rb b/app/services/merge_requests/base_service.rb
index e6837a18696..9d7fca6882d 100644
--- a/app/services/merge_requests/base_service.rb
+++ b/app/services/merge_requests/base_service.rb
@@ -38,5 +38,30 @@ module MergeRequests
     def filter_params
       super(:merge_request)
     end
+
+    def merge_request_from(commit_status)
+      branches = commit_status.ref
+
+      # This is for ref-less builds
+      branches ||= @project.repository.branch_names_contains(commit_status.sha)
+
+      return [] if branches.blank?
+
+      merge_requests = @project.origin_merge_requests.opened.where(source_branch: branches).to_a
+      merge_requests += @project.fork_merge_requests.opened.where(source_branch: branches).to_a
+
+      merge_requests.uniq.select(&:source_project)
+    end
+
+    def each_merge_request(commit_status)
+      merge_request_from(commit_status).each do |merge_request|
+        ci_commit = merge_request.ci_commit
+
+        next unless ci_commit
+        next unless ci_commit.sha == commit_status.sha
+
+        yield merge_request, ci_commit
+      end
+    end
   end
 end
diff --git a/app/services/merge_requests/merge_when_build_succeeds_service.rb b/app/services/merge_requests/merge_when_build_succeeds_service.rb
index d6af12f9739..8fd6a4ea1f6 100644
--- a/app/services/merge_requests/merge_when_build_succeeds_service.rb
+++ b/app/services/merge_requests/merge_when_build_succeeds_service.rb
@@ -20,15 +20,9 @@ module MergeRequests
 
     # Triggers the automatic merge of merge_request once the build succeeds
     def trigger(commit_status)
-      merge_requests = merge_request_from(commit_status)
-
-      merge_requests.each do |merge_request|
+      each_merge_request(commit_status) do |merge_request, ci_commit|
         next unless merge_request.merge_when_build_succeeds?
         next unless merge_request.mergeable?
-
-        ci_commit = merge_request.ci_commit
-        next unless ci_commit
-        next unless ci_commit.sha == commit_status.sha
         next unless ci_commit.success?
 
         MergeWorker.perform_async(merge_request.id, merge_request.merge_user_id, merge_request.merge_params)
@@ -47,20 +41,5 @@ module MergeRequests
       end
     end
 
-    private
-
-    def merge_request_from(commit_status)
-      branches = commit_status.ref
-
-      # This is for ref-less builds
-      branches ||= @project.repository.branch_names_contains(commit_status.sha)
-
-      return [] if branches.blank?
-
-      merge_requests = @project.origin_merge_requests.opened.where(source_branch: branches).to_a
-      merge_requests += @project.fork_merge_requests.opened.where(source_branch: branches).to_a
-
-      merge_requests.uniq.select(&:source_project)
-    end
   end
 end
diff --git a/app/services/merge_requests/refresh_service.rb b/app/services/merge_requests/refresh_service.rb
index 8b3d56c2b4c..fe0579744b4 100644
--- a/app/services/merge_requests/refresh_service.rb
+++ b/app/services/merge_requests/refresh_service.rb
@@ -12,6 +12,7 @@ module MergeRequests
       close_merge_requests
       reload_merge_requests
       reset_merge_when_build_succeeds
+      mark_pending_todos_done
 
       # Leave a system note if a branch was deleted/added
       if branch_added? || branch_removed?
@@ -80,6 +81,12 @@ module MergeRequests
       merge_requests_for_source_branch.each(&:reset_merge_when_build_succeeds)
     end
 
+    def mark_pending_todos_done
+      merge_requests_for_source_branch.each do |merge_request|
+        todo_service.merge_request_push(merge_request, @current_user)
+      end
+    end
+
     def find_new_commits
       if branch_added?
         @commits = []
diff --git a/app/services/todo_service.rb b/app/services/todo_service.rb
index 42c5bca90fd..4bf4e144727 100644
--- a/app/services/todo_service.rb
+++ b/app/services/todo_service.rb
@@ -80,6 +80,30 @@ class TodoService
     mark_pending_todos_as_done(merge_request, current_user)
   end
 
+  # When a build fails on the HEAD of a merge request we should:
+  #
+  #  * create a todo for that user to fix it
+  #
+  def merge_request_build_failed(merge_request)
+    create_build_failed_todo(merge_request)
+  end
+
+  # When a new commit is pushed to a merge request we should:
+  #
+  #  * mark all pending todos related to the merge request for that user as done
+  #
+  def merge_request_push(merge_request, current_user)
+    mark_pending_todos_as_done(merge_request, current_user)
+  end
+
+  # 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
+  #
+  def merge_request_build_retried(merge_request)
+    mark_pending_todos_as_done(merge_request, merge_request.author)
+  end
+
   # When create a note we should:
   #
   #  * mark all pending todos related to the noteable for the note author as done
@@ -145,6 +169,12 @@ class TodoService
     create_todos(mentioned_users, attributes)
   end
 
+  def create_build_failed_todo(merge_request)
+    author = merge_request.author
+    attributes = attributes_for_todo(merge_request.project, merge_request, author, Todo::BUILD_FAILED)
+    create_todos(author, attributes)
+  end
+
   def attributes_for_target(target)
     attributes = {
       project_id: target.project.id,