Add description to schema parser and printer

Descriptions are now part of the [graphql spec](https://facebook.github.io/graphql/June2018/#sec-Descriptions).
This commit brings graphql-core inline with the spec.

graphql/language/ast.py

@@ -543,13 +543,14 @@ def __hash__(self):
 
 
 class StringValue(Value):
- __slots__ = ("loc", "value")
+ __slots__ = ("loc", "value", "is_block_string")
  _fields = ("value",)
 
- def __init__(self, value, loc=None):
+ def __init__(self, value, loc=None, is_block_string=False):
  # type: (str, Optional[Loc]) -> None
  self.loc = loc
  self.value = value
+ self.is_block_string = is_block_string
 
  def __eq__(self, other):
  # type: (Any) -> bool
@@ -989,7 +990,7 @@ def __hash__(self):
 
 
 class ObjectTypeDefinition(TypeDefinition):
- __slots__ = ("loc", "name", "interfaces", "directives", "fields")
+ __slots__ = ("loc", "name", "interfaces", "directives", "fields", "description")
  _fields = ("name", "interfaces", "fields")
 
  def __init__(
@@ -999,19 +1000,20 @@ def __init__(
  interfaces=None, # type: Optional[List[NamedType]]
  loc=None, # type: Optional[Loc]
  directives=None, # type: Optional[List[Directive]]
+ description=None, # type: Optional[String]
  ):
  # type: (...) -> None
  self.loc = loc
  self.name = name
  self.interfaces = interfaces
  self.fields = fields
  self.directives = directives
+ self.description = description
 
  def __eq__(self, other):
  # type: (Any) -> bool
  return self is other or (
- isinstance(other, ObjectTypeDefinition)
- and
+ isinstance(other, ObjectTypeDefinition) and
  # self.loc == other.loc and
  self.name == other.name
  and self.interfaces == other.interfaces
@@ -1042,7 +1044,7 @@ def __hash__(self):
 
 
 class FieldDefinition(Node):
- __slots__ = ("loc", "name", "arguments", "type", "directives")
+ __slots__ = ("loc", "name", "arguments", "type", "directives", "description")
  _fields = ("name", "arguments", "type")
 
  def __init__(
@@ -1052,13 +1054,15 @@ def __init__(
  type, # type: Union[NamedType, NonNullType, ListType]
  loc=None, # type: Optional[Loc]
  directives=None, # type: Optional[List]
+ description=None, # type: Optional[String]
  ):
  # type: (...) -> None
  self.loc = loc
  self.name = name
  self.arguments = arguments
  self.type = type
  self.directives = directives
+ self.description = description
 
  def __eq__(self, other):
  # type: (Any) -> bool
@@ -1094,7 +1098,7 @@ def __hash__(self):
 
 
 class InputValueDefinition(Node):
- __slots__ = ("loc", "name", "type", "default_value", "directives")
+ __slots__ = ("loc", "name", "type", "default_value", "directives", "description")
  _fields = ("name", "type", "default_value")
 
  def __init__(
@@ -1104,13 +1108,15 @@ def __init__(
  default_value=None, # type: Any
  loc=None, # type: Optional[Loc]
  directives=None, # type: Optional[List]
+ description=None, # type: Optional[String]
  ):
  # type: (...) -> None
  self.loc = loc
  self.name = name
  self.type = type
  self.default_value = default_value
  self.directives = directives
+ self.description = description
 
  def __eq__(self, other):
  # type: (Any) -> bool
@@ -1147,7 +1153,7 @@ def __hash__(self):
 
 
 class InterfaceTypeDefinition(TypeDefinition):
- __slots__ = ("loc", "name", "fields", "directives")
+ __slots__ = ("loc", "name", "fields", "directives", "description")
  _fields = ("name", "fields")
 
  def __init__(
@@ -1156,12 +1162,14 @@ def __init__(
  fields, # type: List[FieldDefinition]
  loc=None, # type: Optional[Loc]
  directives=None, # type: Optional[List[Directive]]
+ description=None, # type: Optional[String]
  ):
  # type: (...) -> None
  self.loc = loc
  self.name = name
  self.fields = fields
  self.directives = directives
+ self.description = description
 
  def __eq__(self, other):
  # type: (Any) -> bool
@@ -1194,7 +1202,7 @@ def __hash__(self):
 
 
 class UnionTypeDefinition(TypeDefinition):
- __slots__ = ("loc", "name", "types", "directives")
+ __slots__ = ("loc", "name", "types", "directives", "description")
  _fields = ("name", "types")
 
  def __init__(
@@ -1203,12 +1211,14 @@ def __init__(
  types, # type: List[NamedType]
  loc=None, # type: Optional[Loc]
  directives=None, # type: Optional[List[Directive]]
+ description=None, # type: Optional[String]
  ):
  # type: (...) -> None
  self.loc = loc
  self.name = name
  self.types = types
  self.directives = directives
+ self.description = description
 
  def __eq__(self, other):
  # type: (Any) -> bool
@@ -1241,19 +1251,21 @@ def __hash__(self):
 
 
 class ScalarTypeDefinition(TypeDefinition):
- __slots__ = ("loc", "name", "directives")
+ __slots__ = ("loc", "name", "directives", "description")
  _fields = ("name",)
 
  def __init__(
  self,
  name, # type: Name
  loc=None, # type: Optional[Loc]
  directives=None, # type: Optional[List[Directive]]
+ description=None, # type: Optional[String]
  ):
  # type: (...) -> None
  self.loc = loc
  self.name = name
  self.directives = directives
+ self.description = description
 
  def __eq__(self, other):
  # type: (Any) -> bool
@@ -1284,7 +1296,7 @@ def __hash__(self):
 
 
 class EnumTypeDefinition(TypeDefinition):
- __slots__ = ("loc", "name", "values", "directives")
+ __slots__ = ("loc", "name", "values", "directives", "description")
  _fields = ("name", "values")
 
  def __init__(
@@ -1293,12 +1305,14 @@ def __init__(
  values, # type: List[EnumValueDefinition]
  loc=None, # type: Optional[Loc]
  directives=None, # type: Optional[List[Directive]]
+ description=None, # type: Optional[String]
  ):
  # type: (...) -> None
  self.loc = loc
  self.name = name
  self.values = values
  self.directives = directives
+ self.description = description
 
  def __eq__(self, other):
  # type: (Any) -> bool
@@ -1331,19 +1345,21 @@ def __hash__(self):
 
 
 class EnumValueDefinition(Node):
- __slots__ = ("loc", "name", "directives")
+ __slots__ = ("loc", "name", "directives", "description")
  _fields = ("name",)
 
  def __init__(
  self,
  name, # type: Name
  loc=None, # type: Optional[Loc]
  directives=None, # type: Optional[List[Directive]]
+ description=None, # type: Optional[String]
  ):
  # type: (...) -> None
  self.loc = loc
  self.name = name
  self.directives = directives
+ self.description = description
 
  def __eq__(self, other):
  # type: (Any) -> bool
@@ -1374,7 +1390,7 @@ def __hash__(self):
 
 
 class InputObjectTypeDefinition(TypeDefinition):
- __slots__ = ("loc", "name", "fields", "directives")
+ __slots__ = ("loc", "name", "fields", "directives", "description")
  _fields = ("name", "fields")
 
  def __init__(
@@ -1383,12 +1399,14 @@ def __init__(
  fields, # type: List[InputValueDefinition]
  loc=None, # type: Optional[Loc]
  directives=None, # type: Optional[List[Directive]]
+ description=None, # type: Optional[String]
  ):
  # type: (...) -> None
  self.loc = loc
  self.name = name
  self.fields = fields
  self.directives = directives
+ self.description = description
 
  def __eq__(self, other):
  # type: (Any) -> bool
@@ -1454,7 +1472,7 @@ def __hash__(self):
 
 
 class DirectiveDefinition(TypeSystemDefinition):
- __slots__ = ("loc", "name", "arguments", "locations")
+ __slots__ = ("loc", "name", "arguments", "locations", "description")
  _fields = ("name", "locations")
 
  def __init__(
@@ -1463,12 +1481,14 @@ def __init__(
  locations, # type: List[Name]
  arguments=None, # type: Optional[List[InputValueDefinition]]
  loc=None, # type: Optional[Loc]
+ description=None, # type: Optional[String]
  ):
  # type: (...) -> None
  self.name = name
  self.locations = locations
  self.loc = loc
  self.arguments = arguments
+ self.description = description
 
  def __eq__(self, other):
  # type: (Any) -> bool