Log `used_fields` information on GraphQL API

Put `used_fields` and `used_deprecated_fields` information into logs on
GraphQL API.

lib/gitlab/graphql/query_analyzers/logger_analyzer.rb

@@ -6,6 +6,8 @@ module Gitlab
       class LoggerAnalyzer
         COMPLEXITY_ANALYZER = GraphQL::Analysis::QueryComplexity.new { |query, complexity_value| complexity_value }
         DEPTH_ANALYZER = GraphQL::Analysis::QueryDepth.new { |query, depth_value| depth_value }
+        FIELD_USAGE_ANALYZER = GraphQL::Analysis::FieldUsage.new { |query, used_fields, used_deprecated_fields| [used_fields, used_deprecated_fields] }
+        ALL_ANALYZERS = [COMPLEXITY_ANALYZER, DEPTH_ANALYZER, FIELD_USAGE_ANALYZER].freeze
 
         def analyze?(query)
           Feature.enabled?(:graphql_logging, default_enabled: true)
@@ -29,12 +31,13 @@ module Gitlab
         def final_value(memo)
           return if memo.nil?
 
-          analyzers = [COMPLEXITY_ANALYZER, DEPTH_ANALYZER]
-          complexity, depth = GraphQL::Analysis.analyze_query(memo[:query], analyzers)
+          complexity, depth, field_usages = GraphQL::Analysis.analyze_query(memo[:query], ALL_ANALYZERS)
 
           memo[:depth] = depth
           memo[:complexity] = complexity
           memo[:duration_s] = duration(memo[:time_started]).round(1)
+          memo[:used_fields] = field_usages.first
+          memo[:used_deprecated_fields] = field_usages.second
 
           GraphqlLogger.info(memo.except!(:time_started, :query))
         rescue => e

spec/lib/gitlab/graphql/query_analyzers/logger_analyzer_spec.rb

@@ -26,7 +26,7 @@ RSpec.describe Gitlab::Graphql::QueryAnalyzers::LoggerAnalyzer do
       end
 
       it 'returns a duration in seconds' do
-        allow(GraphQL::Analysis).to receive(:analyze_query).and_return([4, 2])
+        allow(GraphQL::Analysis).to receive(:analyze_query).and_return([4, 2, [[], []]])
         allow(Gitlab::Metrics::System).to receive(:monotonic_time).and_return(monotonic_time_before, monotonic_time_after)
         allow(Gitlab::GraphqlLogger).to receive(:info)
 

spec/requests/api/graphql/gitlab_schema_spec.rb

@@ -190,7 +190,9 @@ RSpec.describe 'GitlabSchema configurations' do
         variables: {}.to_s,
         complexity: 181,
         depth: 13,
-        duration_s: 7
+        duration_s: 7,
+        used_fields: an_instance_of(Array),
+        used_deprecated_fields: an_instance_of(Array)
       }
 
       expect_any_instance_of(Gitlab::Graphql::QueryAnalyzers::LoggerAnalyzer).to receive(:duration).and_return(7)

spec/requests/api/graphql_spec.rb

@@ -9,7 +9,15 @@ RSpec.describe 'GraphQL' do
   context 'logging' do
     shared_examples 'logging a graphql query' do
       let(:expected_params) do
-        { query_string: query, variables: variables.to_s, duration_s: anything, depth: 1, complexity: 1 }
+        {
+          query_string: query,
+          variables: variables.to_s,
+          duration_s: anything,
+          depth: 1,
+          complexity: 1,
+          used_fields: ['Query.echo'],
+          used_deprecated_fields: []
+        }
       end
 
       it 'logs a query with the expected params' do