1 files changed, 73 insertions, 0 deletions
diff --git a/spec/support/graphql/field_selection.rb b/spec/support/graphql/field_selection.rb
new file mode 100644
index 00000000000..e2a3334acac
--- /dev/null
+++ b/spec/support/graphql/field_selection.rb
@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+module Graphql
+  class FieldSelection
+    delegate :empty?, :blank?, :to_h, to: :selection
+    delegate :size, to: :paths
+
+    attr_reader :selection
+
+    def initialize(selection = {})
+      @selection = selection.to_h
+    end
+
+    def to_s
+      serialize_field_selection(selection)
+    end
+
+    def paths
+      selection.flat_map do |field, subselection|
+        paths_in([field], subselection)
+      end
+    end
+
+    private
+
+    def paths_in(path, leaves)
+      return [path] if leaves.nil?
+
+      leaves.to_a.flat_map do |k, v|
+        paths_in([k], v).map { |tail| path + tail }
+      end
+    end
+
+    def serialize_field_selection(hash, level = 0)
+      indent = ' ' * level
+
+      hash.map do |field, subselection|
+        if subselection.nil?
+          "#{indent}#{field}"
+        else
+          subfields = serialize_field_selection(subselection, level + 1)
+          "#{indent}#{field} {\n#{subfields}\n#{indent}}"
+        end
+      end.join("\n")
+    end
+
+    NO_SKIP = ->(_name, _field) { false }
+
+    def self.select_fields(type, skip = NO_SKIP, parent_types = Set.new, max_depth = 3)
+      return new if max_depth <= 0
+
+      new(type.fields.flat_map do |name, field|
+        next [] if skip[name, field]
+
+        inspected = ::Graphql::FieldInspection.new(field)
+        singular_field_type = inspected.type
+
+        # If field type is the same as parent type, then we're hitting into
+        # mutual dependency. Break it from infinite recursion
+        next [] if parent_types.include?(singular_field_type)
+
+        if inspected.nested_fields?
+          subselection = select_fields(singular_field_type, skip, parent_types | [type], max_depth - 1)
+          next [] if subselection.empty?
+
+          [[name, subselection.to_h]]
+        else
+          [[name, nil]]
+        end
+      end)
+    end
+  end
+end