Also handle arrays with skips in them

Author: rmosolgo

lib/graphql/execution/interpreter/runtime.rb

@@ -45,6 +45,25 @@ def []=(key, value)
 
         class GraphQLResultArray < Array
           include GraphQLResult
+
+          def skip_at(index)
+            # Mark this index as dead. It's tricky because some indices may already be storing
+            # `Lazy`s. So the runtime is still holding indexes _before_ skipping,
+            # this object has to coordinate incoming writes to account for any already-skipped indices.
+            @skip_indices ||= []
+            @skip_indices << index
+            offset_by = @skip_indices.count { |skipped_idx| skipped_idx < index}
+            delete_at_index = index - offset_by
+            delete_at(delete_at_index)
+          end
+
+          def []=(idx, value)
+            if @skip_indices
+              offset_by = @skip_indices.count { |skipped_idx| skipped_idx < idx }
+              idx -= offset_by
+            end
+            super(idx, value)
+          end
         end
 
         class GraphQLSelectionSet < Hash
@@ -522,7 +541,7 @@ def continue_value(path, value, parent_type, field, is_non_null, ast_node, resul
               when Hash
                 selection_result.delete(result_name)
               when Array
-                selection_result.delete_at(result_name)
+                selection_result.skip_at(result_name)
               else
                 raise "Invariant: unexpected result class #{selection_result.class} (#{selection_result.inspect})"
               end

spec/graphql/execution/interpreter_spec.rb

@@ -564,6 +564,17 @@ def skip
         def lazy_skip
           -> { context.skip }
         end
+
+        field :mixed_skips, [String], null: true
+        def mixed_skips
+          [
+            "a",
+            context.skip,
+            "c",
+            -> { context.skip },
+            "e",
+          ]
+        end
       end
 
       class NothingSubscription < GraphQL::Schema::Subscription
@@ -592,6 +603,10 @@ class Subscription < GraphQL::Schema::Object
       assert_equal({}, res["data"])
       refute res.key?("errors")
 
+      res = LazySkipSchema.execute("{ mixedSkips }")
+      assert_equal({ "mixedSkips" => ["a", "c", "e"] }, res["data"])
+      refute res.key?("errors")
+
       res = LazySkipSchema.execute("{ lazySkip }")
       assert_equal({}, res["data"])
       refute res.key?("errors")