Add mutation toggling WIP state of merge requests

This is mainly the setup of mutations for GraphQL. Including
authorization and basic return type-structure.

6 files changed, 99 insertions, 2 deletions

diff --git a/app/graphql/gitlab_schema.rb b/app/graphql/gitlab_schema.rb
index d9f9129d08a..8755a1a62e7 100644
--- a/app/graphql/gitlab_schema.rb
+++ b/app/graphql/gitlab_schema.rb
@@ -7,5 +7,5 @@ class GitlabSchema < GraphQL::Schema
   query(Types::QueryType)
 
   default_max_page_size 100
-  # mutation(Types::MutationType)
+  mutation(Types::MutationType)
 end
diff --git a/app/graphql/mutations/base_mutation.rb b/app/graphql/mutations/base_mutation.rb
new file mode 100644
index 00000000000..eb03dfe1624
--- /dev/null
+++ b/app/graphql/mutations/base_mutation.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+module Mutations
+  class BaseMutation < GraphQL::Schema::RelayClassicMutation
+    field :errors, [GraphQL::STRING_TYPE],
+          null: false,
+          description: "Reasons why the mutation failed."
+
+    def current_user
+      context[:current_user]
+    end
+  end
+end
diff --git a/app/graphql/mutations/concerns/mutations/resolves_project.rb b/app/graphql/mutations/concerns/mutations/resolves_project.rb
new file mode 100644
index 00000000000..0dd1f264a52
--- /dev/null
+++ b/app/graphql/mutations/concerns/mutations/resolves_project.rb
@@ -0,0 +1,13 @@
+module Mutations
+  module ResolvesProject
+    extend ActiveSupport::Concern
+
+    def resolve_project(full_path:)
+      resolver.resolve(full_path: full_path)
+    end
+
+    def resolver
+      Resolvers::ProjectResolver.new(object: nil, context: context)
+    end
+  end
+end
diff --git a/app/graphql/mutations/merge_requests/base.rb b/app/graphql/mutations/merge_requests/base.rb
new file mode 100644
index 00000000000..2149e72e2df
--- /dev/null
+++ b/app/graphql/mutations/merge_requests/base.rb
@@ -0,0 +1,32 @@
+module Mutations
+  module MergeRequests
+    class Base < BaseMutation
+      include Gitlab::Graphql::Authorize::AuthorizeResource
+      include Mutations::ResolvesProject
+
+      argument :project_path, GraphQL::ID_TYPE,
+               required: true,
+               description: "The project the merge request to mutate is in"
+
+      argument :iid, GraphQL::ID_TYPE,
+               required: true,
+               description: "The iid of the merge request to mutate"
+
+      field :merge_request,
+            Types::MergeRequestType,
+            null: true,
+            description: "The merge request after mutation"
+
+      authorize :update_merge_request
+
+      private
+
+      def find_object(project_path:, iid:)
+        project = resolve_project(full_path: project_path)
+        resolver = Resolvers::MergeRequestResolver.new(object: project, context: context)
+
+        resolver.resolve(iid: iid)
+      end
+    end
+  end
+end
diff --git a/app/graphql/mutations/merge_requests/set_wip.rb b/app/graphql/mutations/merge_requests/set_wip.rb
new file mode 100644
index 00000000000..a2aa0c84ee4
--- /dev/null
+++ b/app/graphql/mutations/merge_requests/set_wip.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+module Mutations
+  module MergeRequests
+    class SetWip < Base
+      graphql_name 'MergeRequestSetWip'
+
+      argument :wip,
+               GraphQL::BOOLEAN_TYPE,
+               required: true,
+               description: <<~DESC
+                            Whether or not to set the merge request as a WIP.
+                            DESC
+
+      def resolve(project_path:, iid:, wip: nil)
+        merge_request = authorized_find!(project_path: project_path, iid: iid)
+        project = merge_request.project
+
+        ::MergeRequests::UpdateService.new(project, current_user, wip_event: wip_event(merge_request, wip))
+          .execute(merge_request)
+
+        {
+          merge_request: merge_request,
+          errors: merge_request.errors.full_messages
+        }
+      end
+
+      private
+
+      def wip_event(merge_request, wip)
+        wip ? 'wip' : 'unwip'
+      end
+    end
+  end
+end
diff --git a/app/graphql/types/mutation_type.rb b/app/graphql/types/mutation_type.rb
index 06ed91c1658..2b4ef299296 100644
--- a/app/graphql/types/mutation_type.rb
+++ b/app/graphql/types/mutation_type.rb
@@ -1,7 +1,11 @@
+# frozen_string_literal: true
+
 module Types
   class MutationType < BaseObject
+    include Gitlab::Graphql::MountMutation
+
     graphql_name "Mutation"
 
-    # TODO: Add Mutations as fields
+    mount_mutation Mutations::MergeRequests::SetWip
   end
 end