Add field usage query analyzer

Author: cjoudrey

lib/graphql/analysis.rb

@@ -3,3 +3,4 @@
 require "graphql/analysis/query_complexity"
 require "graphql/analysis/query_depth"
 require "graphql/analysis/analyze_query"
+require "graphql/analysis/field_usage"

lib/graphql/analysis/field_usage.rb

@@ -0,0 +1,44 @@
+module GraphQL
+  module Analysis
+    # A query reducer for tracking both field usage and deprecated field usage.
+    #
+    # @example Logging field usage and deprecated field usage
+    #   Schema.query_analyzers << GraphQL::Analysis::FieldUsage.new { |query, used_fields, used_deprecated_fields|
+    #     puts "Used GraphQL fields: #{used_fields.join(', ')}"
+    #     puts "Used deprecated GraphQL fields: #{used_deprecated_fields.join(', ')}"
+    #   }
+    #   Schema.execute(query_str)
+    #   # Used GraphQL fields: Cheese.id, Cheese.fatContent, Query.cheese
+    #   # Used deprecated GraphQL fields: Cheese.fatContent
+    #
+    class FieldUsage
+      def initialize(&block)
+        @field_usage_handler = block
+      end
+
+      def initial_value(query)
+        {
+          query: query,
+          used_fields: Set.new,
+          used_deprecated_fields: Set.new
+        }
+      end
+
+      def call(memo, visit_type, irep_node)
+        if irep_node.ast_node.is_a?(GraphQL::Language::Nodes::Field) && visit_type == :leave
+          irep_node.definitions.each do |type_defn, field_defn|
+            field = "#{type_defn.name}.#{field_defn.name}"
+            memo[:used_fields] << field
+            memo[:used_deprecated_fields] << field if field_defn.deprecation_reason
+          end
+        end
+
+        memo
+      end
+
+      def final_value(memo)
+        @field_usage_handler.call(memo[:query], memo[:used_fields].to_a, memo[:used_deprecated_fields].to_a)
+      end
+    end
+  end
+end

spec/graphql/analysis/field_usage_spec.rb

@@ -0,0 +1,61 @@
+require "spec_helper"
+
+describe GraphQL::Analysis::FieldUsage do
+  let(:result) { [] }
+  let(:field_usage_analyzer) { GraphQL::Analysis::FieldUsage.new { |query, used_fields, used_deprecated_fields| result << query << used_fields << used_deprecated_fields } }
+  let(:reduce_result) { GraphQL::Analysis.analyze_query(query, [field_usage_analyzer]) }
+  let(:query) { GraphQL::Query.new(DummySchema, query_string, variables: variables) }
+  let(:variables) { {} }
+
+  describe "query with deprecated fields" do
+    let(:query_string) {%|
+      query {
+        cheese(id: 1) {
+          id
+          fatContent
+        }
+      }
+    |}
+
+    it "returns query in reduced result" do
+      reduce_result
+      assert_equal query, result[0]
+    end
+
+    it "keeps track of used fields" do
+      reduce_result
+      assert_equal ['Cheese.id', 'Cheese.fatContent', 'Query.cheese'], result[1]
+    end
+
+    it "keeps track of deprecated fields" do
+      reduce_result
+      assert_equal ['Cheese.fatContent'], result[2]
+    end
+  end
+
+  describe "query with deprecated fields used more than once" do
+    let(:query_string) {%|
+      query {
+        cheese1: cheese(id: 1) {
+          id
+          fatContent
+        }
+
+        cheese2: cheese(id: 2) {
+          id
+          fatContent
+        }
+      }
+    |}
+
+    it "omits duplicate usage of a field" do
+      reduce_result
+      assert_equal ['Cheese.id', 'Cheese.fatContent', 'Query.cheese'], result[1]
+    end
+
+    it "omits duplicate usage of a deprecated field" do
+      reduce_result
+      assert_equal ['Cheese.fatContent'], result[2]
+    end
+  end
+end