Canopy GraphQL.peg

# This is the PEG-based grammar for GraphQL based on:
# https://spec.graphql.org/October2021/#sec-Document-Syntax
#
# It is also inspired by another PEG grammar of GraphQL for JavaScript:
# https://github.com/madjam002/graphqlite/blob/master/grammar.pegjs
#
# This only complies with the GraphQL spec with no further additions, focusing
# only the **Executable Definitions**, to optimize the output and processing

grammar Rails.GraphQL.Parser
  ## ROOT
  # Collect all definitions ignoring whitespaces
  document <- @ows definitions:definition+ @ows

  # MAIN TREE
  definition <- operation / fragment

  operation <- (type:operation_type @rws)? (name @rws)? variables? directives? selection
  fragment <- "fragment" @rws (!"on" name) @rws "on" @rws type:name directives? @rws selection
  operation_type <- "query" / "mutation" / "subscription"

  selection <- @op_object items:selection_item* @cl_object
  selection_item <- (field / fragment_spread / inline_fragment) @field_sep

  field <- (alias:name @key_sep)? name arguments? directives? selection?
  fragment_spread <- "..." @ows name directives?
  inline_fragment <- "..." @ows ((!"on" name) @rws "on" @rws type:name)? directives? selection

  directives <- @rws "@" name arguments?
  variables <- op_parent variable* cl_parent
  arguments <- op_parent argument* cl_parent

  variable <- "$" name @key_sep type:generic_type (eql_sep value)? directives?
  argument <- name @key_sep (value / ("$" var_name:name))

  generic_type <- name / not_null_type / list_type
  not_null_type <- (name / list_type) "!"
  list_type <- op_list generic_type cl_list

  # FORMATTING
  # The definition of whitespaces (o => optional, r => required) and comments
  ws <- [ \t\n\r] / comment
  comment <- "#" [^\n]*
  ows <- ws*
  rws <- ws+

  ## SEPARATORS
  # Some common separators
  op_object <- @ows @"{" @ows
  cl_object <- @ows @"}" @ows
  op_parent <- @ows @"(" @ows
  cl_parent <- @ows @")" @ows
  op_list <- @ows @"[" @ows
  cl_list <- @ows @"]" @ows
  key_sep <- @ows @":" @ows
  eql_sep <- @ows @"=" @ows
  item_sep <- @ows @"," @ows
  field_sep <- @ows @","* @ows

  # IDENTIFIERS
  # Name based identifiers
  name <- [a-zA-Z_] [0-9a-zA-Z_]*
  value <- int_number / float_number / string / boolean / null / enum / list_value / object_value

  int_number   <- "-"? int
  float_number <- int_number fraction? exponent?
  string       <- inline_string / multiline_string
  boolean      <- "true" / "false"
  null         <- "null"
  enum         <- name
  list_value   <- @op_list items:(value (@item_sep value)*)? @cl_list
  object_value <- @op_object items:(object_field (@item_sep object_field)*)? @cl_object

  # Numeric helpers
  digit <- [0-9]
  int <- "0" / ([1-9] digit*)
  fraction <- @"." value:(digit+)
  exponent <- [eE] value:(("+" / "-")? digit+)

  # String helpers
  char <- [\u0009\u000A\u000D\u0020-\uFFFF] / escaped_char
  escaped_char <- "\\" ([\u0056\u002F\u0062\u0066\u006E\u0072\u0074] / ("u" code:[0-9a-fA-F]{4}))
  inline_string <- '"' char* '"'
  multiline_string <- '"""' char* '"""'

  # Hash helper
  object_field <- name @key_sep value