New logfile for graphql queries

Specify dedicated logfile and logger class for GraphQL queries. Move
complexity analyzer to a dedicated class.

lib/gitlab/graphql/query_analyzers/log_query_complexity.rb

@@ -8,7 +8,7 @@ module Gitlab
           def analyzer
             GraphQL::Analysis::QueryComplexity.new do |query, complexity|
               # temporary until https://gitlab.com/gitlab-org/gitlab-ce/issues/59587
-              Rails.logger.info("[GraphQL Query Complexity] #{complexity}  | admin? #{query.context[:current_user]&.admin?}")
+              GraphqlLogger.info("[Query Complexity] #{complexity}  | admin? #{query.context[:current_user]&.admin?}")
             end
           end
         end

lib/gitlab/graphql_logger.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module Gitlab
+  class GraphqlLogger < Gitlab::Logger
+    def self.file_name_noext
+      'graphql_json'
+    end
+
+    # duration
+    # complexity
+    # depth
+    # sanitized variables (?)
+    # a structured representation of the query (?)
+
+    def format_message(severity, timestamp, progname, msg)
+      "#{timestamp.to_s(:long)}: #{msg}\n"
+    end
+  end
+end

spec/lib/gitlab/graphql_logger_spec.rb

@@ -0,0 +1,21 @@
+require 'spec_helper'
+
+describe Gitlab::GraphqlLogger, :request_store do
+  subject { described_class.new('/dev/null') }
+  let(:now) { Time.now }
+
+  it 'builds a logger once' do
+    expect(::Logger).to receive(:new).and_call_original
+
+    subject.info('hello world')
+    subject.error('hello again')
+  end
+
+  describe '#format_message' do
+    it 'formats properly' do
+      output = subject.format_message('INFO', now, 'test', 'Hello world')
+
+      expect(output).to match(/Hello world/)
+    end
+  end
+end

spec/requests/api/graphql/gitlab_schema_spec.rb

@@ -83,6 +83,16 @@ describe 'GitlabSchema configurations' do
     end
   end
 
+  context 'logging' do
+    it 'writes to the GraphQL log' do
+      expect(Gitlab::GraphqlLogger).to receive(:info).with(/Query Complexity/)
+
+      query = File.read(Rails.root.join('spec/fixtures/api/graphql/introspection.graphql'))
+
+      post_graphql(query, current_user: nil)
+    end
+  end
+
   context 'when IntrospectionQuery' do
     it 'is not too complex' do
       query = File.read(Rails.root.join('spec/fixtures/api/graphql/introspection.graphql'))