Add `present_using` to types

By specifying a presenter for the object type, we can keep the logic
out of `GitlabSchema`.

The presenter gets initialized using the object being presented, and
the context (including the `current_user`).

app/graphql/gitlab_schema.rb

 Gitlab::Graphql::Authorize.register!
+Gitlab::Graphql::Present.register!
 GitlabSchema = GraphQL::Schema.define do
   use BatchLoader::GraphQL
   enable_preloading
   enable_authorization
-  mutation(Types::MutationType)
+  enable_presenting
   query(Types::QueryType)
 end

app/graphql/types/merge_request_type.rb

 Types::MergeRequestType = GraphQL::ObjectType.define do
+  present_using MergeRequestPresenter
+
   name 'MergeRequest'
   field :id, !types.ID
   field :iid, !types.ID
-  field :title, types.String
+  field :title, !types.String
   field :description, types.String
   field :state, types.String
-
-  field :created_at, Types::TimeType
-  field :updated_at, Types::TimeType
-
-  field :source_project, -> { Types::ProjectType }
-  field :target_project, -> { Types::ProjectType }
-
+  field :created_at, !Types::TimeType
+  field :updated_at, !Types::TimeType
+  field :source_project, Types::ProjectType
+  field :target_project, !Types::ProjectType
   # Alias for target_project
-  field :project, -> { Types::ProjectType }
-
+  field :project, !Types::ProjectType
+  field :project_id, !types.Int, property: :target_project_id
   field :source_project_id, types.Int
-  field :target_project_id, types.Int
-  field :project_id, types.Int
-
-  field :source_branch, types.String
-  field :target_branch, types.String
-
+  field :target_project_id, !types.Int
+  field :source_branch, !types.String
+  field :target_branch, !types.String
   field :work_in_progress, types.Boolean, property: :work_in_progress?
   field :merge_when_pipeline_succeeds, types.Boolean
-
   field :sha, types.String, property: :diff_head_sha
   field :merge_commit_sha, types.String
-
   field :user_notes_count, types.Int
   field :should_remove_source_branch, types.Boolean, property: :should_remove_source_branch?
   field :force_remove_source_branch, types.Boolean, property: :force_remove_source_branch?
-
   field :merge_status, types.String
-
-  field :web_url, types.String do
-    resolve ->(merge_request, args, ctx) { Gitlab::UrlBuilder.build(merge_request) }
-  end
-
+  field :in_progress_merge_commit_sha, types.String
+  field :merge_error, types.String
+  field :allow_maintainer_to_push, types.Boolean
+  field :should_be_rebased, types.Boolean, property: :should_be_rebased?
+  field :rebase_commit_sha, types.String
+  field :rebase_in_progress, types.Boolean, property: :rebase_in_progress?
+  field :diff_head_sha, types.String
+  field :merge_commit_message, types.String
+  field :merge_ongoing, types.Boolean, property: :merge_ongoing?
+  field :work_in_progress, types.Boolean, property: :work_in_progress?
+  field :source_branch_exists, types.Boolean, property: :source_branch_exists?
+  field :mergeable_discussions_state, types.Boolean
+  field :web_url, types.String, property: :web_url
   field :upvotes, types.Int
   field :downvotes, types.Int
-
-  field :subscribed, types.Boolean do
-    resolve ->(merge_request, args, ctx) do
-      merge_request.subscribed?(ctx[:current_user], merge_request.target_project)
-    end
-  end
+  field :subscribed, types.Boolean, property: :subscribed?
 end

app/graphql/types/project_type.rb

@@ -31,6 +31,7 @@ Types::ProjectType = GraphQL::ObjectType.define do
   field :container_registry_enabled, types.Boolean
   field :shared_runners_enabled, types.Boolean
   field :lfs_enabled, types.Boolean
+  field :ff_only_enabled, types.Boolean, property: :merge_requests_ff_only_enabled
   field :avatar_url, types.String do
     resolve ->(project, args, ctx) { project.avatar_url(only_path: false) }

app/presenters/merge_request_presenter.rb

@@ -179,6 +179,25 @@ class MergeRequestPresenter < Gitlab::View::Presenter::Delegated
       .can_push_to_branch?(source_branch)
   end
+  def mergeable_discussions_state
+    # This avoids calling MergeRequest#mergeable_discussions_state without
+    # considering the state of the MR first. If a MR isn't mergeable, we can
+    # safely short-circuit it.
+    if merge_request.mergeable_state?(skip_ci_check: true, skip_discussions_check: true)
+      merge_request.mergeable_discussions_state?
+    else
+      false
+    end
+  end
+
+  def web_url
+    Gitlab::UrlBuilder.build(merge_request)
+  end
+
+  def subscribed?
+    merge_request.subscribed?(current_user, merge_request.target_project)
+  end
+
   private
   def cached_can_be_reverted?

changelogs/unreleased/bvl-graphql-start-34754.yml

+---
+title: Setup graphql with initial project & merge request query
+merge_request: 19008
+author:
+type: added

doc/api/graphql/index.md

+# GraphQL API (Beta)
+
+> [Introduced][ce-19008] in GitLab 11.0.
+
+## Enabling the GraphQL feature
+
+The GraphQL API itself is currently in Beta, and therefore hidden behind a
+feature flag. To enable it on your selfhosted instance, run
+`Feature.enable(:graphql)`.
+
+Start the console by running
+
+```bash
+sudo gitlab-rails console
+```
+
+Then enable the feature by running
+
+```ruby
+Feature.enable(:graphql)
+```
+
+## Available queries
+
+A first iteration of a GraphQL API inlcudes only 2 queries: `project` and
+`merge_request` and only returns scalar fields, or fields of the type `Project`
+or `MergeRequest`.
+
+## GraphiQL
+
+The API can be explored by using the GraphiQL IDE, it is available on your
+instance on `gitlab.example.com/api/graphiql`.
+
+[ce-19008]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/19008

doc/development/README.md

@@ -32,6 +32,8 @@ description: 'Learn how to contribute to GitLab.'
 - [GitLab utilities](utilities.md)
 - [API styleguide](api_styleguide.md) Use this styleguide if you are
   contributing to the API.
+- [GrapQL API styleguide](api_graphql_styleguide.md) Use this
+  styleguide if you are contribution to the [GraphQL API](../api/graphql/index.md)
 - [Sidekiq guidelines](sidekiq_style_guide.md) for working with Sidekiq workers
 - [Working with Gitaly](gitaly.md)
 - [Manage feature flags](feature_flags.md)

doc/development/api_graphql_styleguide.md

+# GraphQL API
+
+## Authentication
+
+Authentication happens through the `GrapqlController`, right now this
+uses the same authentication as the rails application. So the session
+can be shared.
+
+It is also possible to add a `private_token` to the querystring, or
+add a `HTTP_PRIVATE_TOKEN` header.
+
+### Authorization
+
+Fields can be authorized using the same abilities used in the rails
+app. This can be done using the `authorize` helper:
+
+```ruby
+Types::QueryType = GraphQL::ObjectType.define do
+  name 'Query'
+
+  field :project, Types::ProjectType do
+    argument :full_path, !types.ID do
+      description 'The full path of the project, e.g., "gitlab-org/gitlab-ce"'
+    end
+
+    authorize :read_project
+
+    resolve Loaders::FullPathLoader[:project]
+  end
+end
+```
+
+The object found by the resolve call is used for authorization.
+
+
+## Types
+
+When exposing a model through the GraphQL API, we do so by creating a
+new type in `app/graphql/types`.
+
+When exposing properties in a type, make sure to keep the logic inside
+the definition as minimal as possible. Instead, consider moving any
+logic into a presenter:
+
+```ruby
+Types::MergeRequestType = GraphQL::ObjectType.define do
+  present_using MergeRequestPresenter
+
+  name 'MergeRequest'
+end
+```
+
+An existing presenter could be used, but it is also possible to create
+a new presenter specifically for GraphQL.
+
+The presenter is initialized using the object resolved by a field, and
+the context.
+
+## Testing
+
+_full stack_ tests for a graphql query or mutation live in
+`spec/requests/graphql`.
+
+When adding a query, the `a working graphql query` shared example can
+be used to test the query, it expects a valid `query` to be available
+in the spec.

lib/gitlab/graphql/present.rb

+module Gitlab
+  module Graphql
+    class Present
+      PRESENT_USING = -> (type, presenter_class, *args) do
+        type.metadata[:presenter_class] = presenter_class
+      end
+
+      INSTRUMENT_PROC = -> (schema) do
+        schema.instrument(:field, new)
+      end
+
+      def self.register!
+        GraphQL::Schema.accepts_definitions(enable_presenting: INSTRUMENT_PROC)
+        GraphQL::ObjectType.accepts_definitions(present_using: PRESENT_USING)
+      end
+
+      def instrument(type, field)
+        return field unless type.metadata[:presenter_class]
+
+        old_resolver = field.resolve_proc
+
+        resolve_with_presenter = -> (obj, args, context) do
+          presenter = type.metadata[:presenter_class].new(obj, **context.to_h)
+
+          old_resolver.call(presenter, args, context)
+        end
+
+        field.redefine do
+          resolve(resolve_with_presenter)
+        end
+      end
+    end
+  end
+end

spec/graphql/gitlab_schema_spec.rb

@@ -13,7 +13,14 @@ describe GitlabSchema do
     expect(field_instrumenters).to include(instance_of(::Gitlab::Graphql::Authorize))
   end
+  it 'enables using presenters' do
+    expect(field_instrumenters).to include(instance_of(::Gitlab::Graphql::Present))
+  end
+
   it 'has the base mutation' do
+    pending <<~REASON
+      Having empty mutations breaks the automatic documentation in Graphiql, so removed for now."
+    REASON
     expect(described_class.mutation).to eq(::Types::MutationType)
   end

spec/requests/graphql/merge_request_query_spec.rb

+require 'spec_helper'
+
+describe 'getting merge request information' do
+  include GraphqlHelpers
+
+  let(:project) { create(:project, :repository, :public) }
+  let(:merge_request) { create(:merge_request, source_project: project) }
+
+  let(:query) do
+    <<~QUERY
+    {
+      merge_request(project: "#{merge_request.project.full_path}", iid: "#{merge_request.iid}") {
+        #{all_graphql_fields_for(MergeRequest)}
+      }
+    }
+    QUERY
+  end
+
+  it_behaves_like 'a working graphql query' do
+    it 'renders a merge request with all fields' do
+      expect(response_data['merge_request']).not_to be_nil
+    end
+  end
+end

spec/requests/graphql/project_query_spec.rb

+require 'spec_helper'
+
+describe 'getting project information' do
+  include GraphqlHelpers
+
+  let(:project) { create(:project, :repository, :public) }
+
+  let(:query) do
+    <<~QUERY
+    {
+      project(full_path: "#{project.full_path}") {
+        #{all_graphql_fields_for(Project)}
+      }
+    }
+    QUERY
+  end
+
+  it_behaves_like 'a working graphql query' do
+    it 'renders a project with all fields' do
+      expect(response_data['project']).not_to be_nil
+    end
+  end
+end

spec/support/helpers/graphql_helpers.rb

@@ -9,12 +9,12 @@ module GraphqlHelpers
     wrapper = proc do
       begin
         BatchLoader::Executor.ensure_current
-        blk.call
+        yield
       ensure
         BatchLoader::Executor.clear_current
       end
     end
-  
+
     if max_queries
       result = nil
       expect { result = wrapper.call }.not_to exceed_query_limit(max_queries)
@@ -23,4 +23,33 @@ module GraphqlHelpers
       wrapper.call
     end
   end
+
+  def all_graphql_fields_for(klass)
+    type = GitlabSchema.types[klass.name]
+    return "" unless type
+
+    type.fields.map do |name, field|
+      if scalar?(field)
+        name
+      else
+        "#{name} { #{all_graphql_fields_for(field_type(field))} }"
+      end
+    end.join("\n")
+  end
+
+  def post_graphql(query)
+    post '/api/graphql', query: query
+  end
+
+  def scalar?(field)
+    field_type(field).kind.scalar?
+  end
+
+  def field_type(field)
+    if field.type.respond_to?(:of_type)
+      field.type.of_type
+    else
+      field.type
+    end
+  end
 end

spec/support/shared_examples/requests/graphql_shared_examples.rb

+require 'spec_helper'
+
+shared_examples 'a working graphql query' do
+  include GraphqlHelpers
+
+  let(:parsed_response) { JSON.parse(response.body) }
+  let(:response_data) { parsed_response['data'] }
+
+  before do
+    post_graphql(query)
+  end
+
+  it 'is returns a successfull response', :aggregate_failures do
+    expect(response).to be_success
+    expect(parsed_response['errors']).to be_nil
+    expect(response_data).not_to be_empty
+  end
+end