Inline Fragments

inline_fragments.rb

require "bundler/inline"

gemfile do
  gem "graphql", "~>2.0"
end


# This visitor will inline any fragment definitions in the document.
# It assumes that the document is valid; it will :boom: if there are
# cycles in the fragment spreads.
#
# It doesn't deduplicate selections.
class InlineFragments < GraphQL::Language::Visitor
  def on_document(node, _parent)
    # First, build up this map so we can access it later:
    @fragment_definition_nodes = {}
    node.definitions.each do |defn_node|
      if defn_node.is_a?(GraphQL::Language::Nodes::FragmentDefinition)
        @fragment_definition_nodes[defn_node.name] = defn_node
      end
    end
    # And go ahead and flatten definitions
    @fragment_definition_nodes.keys.each do |k|
      @fragment_definition_nodes[k] = replace_fragment_spreads(@fragment_definition_nodes[k])
    end

    super
  end

  def on_operation_definition(node, _parent)
    modified_node = replace_fragment_spreads(node)
    super(modified_node, _parent)
  end

  def on_fragment_definition(node, _parent)
    super(DELETE_NODE, _parent)
  end

  def on_field(node, _parent)
    modified_node = replace_fragment_spreads(node)
    super(modified_node, _parent)
  end

  def on_inline_fragment(node, _parent)
    modified_node = replace_fragment_spreads(node)
    super(modified_node, _parent)
  end

  private

  def replace_fragment_spreads(node)
    new_selections = []
    substituted = false
    node.selections.each do |selection|
      if selection.is_a?(GraphQL::Language::Nodes::FragmentSpread)
        substituted = true
        defn_node = @fragment_definition_nodes[selection.name]
        inline_frag_node = GraphQL::Language::Nodes::InlineFragment.new(
          directives: [],
          selections: defn_node.selections,
          type: defn_node.type,
        )
        new_selections << inline_frag_node
      else
        new_selections << selection
      end
    end

    if substituted
      node.merge(selections: new_selections)
    else
      node
    end
  end
end


# Example:

doc = GraphQL.parse("
{
  ...A1
  ...B1
  field1 {
    field2 {
      ...C1
    }
  }
}

fragment A2 on T {
  fieldA3
  ...C1
}

fragment A1 on T {
  fieldA1
  fieldA2 {
    ...A2
  }
}

fragment B1 on T {
  fieldB1
  ...A1
}

fragment C1 on T {
  ... {
    fieldC1
    fieldC2 {
      ... {
        fieldC3
        ...C2
      }
    }
  }
}

fragment C2 on T {
  fieldC4
}
")


visitor = InlineFragments.new(doc)
visitor.visit

puts visitor.result.to_query_string
# query {
#   ... on T {
#     fieldA1
#     fieldA2 {
#       ... on T {
#         fieldA3
#         ... on T {
#           ... {
#             fieldC1
#             fieldC2 {
#               ... {
#                 fieldC3
#                 ... on T {
#                   fieldC4
#                 }
#               }
#             }
#           }
#         }
#       }
#     }
#   }
#   ... on T {
#     fieldB1
#     ... on T {
#       fieldA1
#       fieldA2 {
#         ... on T {
#           fieldA3
#           ... on T {
#             ... {
#               fieldC1
#               fieldC2 {
#                 ... {
#                   fieldC3
#                   ... on T {
#                     fieldC4
#                   }
#                 }
#               }
#             }
#           }
#         }
#       }
#     }
#   }
#   field1 {
#     field2 {
#       ... on T {
#         ... {
#           fieldC1
#           fieldC2 {
#             ... {
#               fieldC3
#               ... on T {
#                 fieldC4
#               }
#             }
#           }
#         }
#       }
#     }
#   }
# }