support null values

- addresses graphql-python#118
- initial implementation by @yen223 in PR graphql-python#119

Author: jaemk

Diff for: graphql/execution/executor.py

@@ -364,6 +364,9 @@ def resolve_field(
     executor = exe_context.executor
     result = resolve_or_error(resolve_fn_middleware, source, info, args, executor)
 
+    if result is Undefined:
+        return Undefined
+
     return complete_value_catching_error(
         exe_context, return_type, field_asts, info, field_path, result
     )

Diff for: graphql/execution/values.py

@@ -20,6 +20,7 @@
 from ..utils.is_valid_value import is_valid_value
 from ..utils.type_from_ast import type_from_ast
 from ..utils.value_from_ast import value_from_ast
+from ..utils.undefined import Undefined
 
 # Necessary for static type checking
 if False:  # flake8: noqa
@@ -56,10 +57,11 @@ def get_variable_values(
                 [def_ast],
             )
         elif value is None:
-            if def_ast.default_value is not None:
-                values[var_name] = value_from_ast(
-                    def_ast.default_value, var_type
-                )  # type: ignore
+            if def_ast.default_value is None:
+                values[var_name] = None
+            elif def_ast.default_value is not Undefined:
+                values[var_name] = value_from_ast(def_ast.default_value, var_type)
+
             if isinstance(var_type, GraphQLNonNull):
                 raise GraphQLError(
                     'Variable "${var_name}" of required type "{var_type}" was not provided.'.format(
@@ -109,7 +111,7 @@ def get_argument_values(
         arg_type = arg_def.type
         arg_ast = arg_ast_map.get(name)
         if name not in arg_ast_map:
-            if arg_def.default_value is not None:
+            if arg_def.default_value is not Undefined:
                 result[arg_def.out_name or name] = arg_def.default_value
                 continue
             elif isinstance(arg_type, GraphQLNonNull):
@@ -123,7 +125,7 @@ def get_argument_values(
             variable_name = arg_ast.value.name.value  # type: ignore
             if variables and variable_name in variables:
                 result[arg_def.out_name or name] = variables[variable_name]
-            elif arg_def.default_value is not None:
+            elif arg_def.default_value is not Undefined:
                 result[arg_def.out_name or name] = arg_def.default_value
             elif isinstance(arg_type, GraphQLNonNull):
                 raise GraphQLError(
@@ -137,7 +139,7 @@ def get_argument_values(
         else:
             value = value_from_ast(arg_ast.value, arg_type, variables)  # type: ignore
             if value is None:
-                if arg_def.default_value is not None:
+                if arg_def.default_value is not Undefined:
                     value = arg_def.default_value
                     result[arg_def.out_name or name] = value
             else:
@@ -172,7 +174,7 @@ def coerce_value(type, value):
         obj = {}
         for field_name, field in fields.items():
             if field_name not in value:
-                if field.default_value is not None:
+                if field.default_value is not Undefined:
                     field_value = field.default_value
                     obj[field.out_name or field_name] = field_value
             else:

Diff for: graphql/language/ast.py

@@ -604,6 +604,48 @@ def __hash__(self):
         return id(self)
 
 
+class NullValue(Value):
+    __slots__ = ("loc", "value")
+    _fields = ("value",)
+
+    def __init__(self, value=None, loc=None):
+        self.value = None
+        self.loc = loc
+
+    def __eq__(self, other):
+        return isinstance(other, NullValue)
+
+    def __repr__(self):
+        return "NullValue"
+
+    def __copy__(self):
+        return type(self)(self.value, self.loc)
+
+    def __hash__(self):
+        return id(self)
+
+
+class UndefinedValue(Value):
+    __slots__ = ("loc", "value")
+    _fields = ("value",)
+
+    def __init__(self, value=None, loc=None):
+        self.value = None
+        self.loc = loc
+
+    def __eq__(self, other):
+        return isinstance(other, UndefinedValue)
+
+    def __repr__(self):
+        return "UndefinedValue"
+
+    def __copy__(self):
+        return type(self)(self.value, self.loc)
+
+    def __hash__(self):
+        return id(self)
+
+
 class EnumValue(Value):
     __slots__ = ("loc", "value")
     _fields = ("value",)

Diff for: graphql/language/parser.py

@@ -4,6 +4,7 @@
 from ..error import GraphQLSyntaxError
 from .lexer import Lexer, TokenKind, get_token_desc, get_token_kind_desc
 from .source import Source
+from ..utils.undefined import Undefined
 
 # Necessary for static type checking
 if False:  # flake8: noqa
@@ -65,6 +66,12 @@ def parse(source, **kwargs):
 
 
 def parse_value(source, **kwargs):
+    if source is None:
+        return ast.NullValue()
+
+    if source is Undefined:
+        return ast.UndefinedValue()
+
     options = {"no_location": False, "no_source": False}
     options.update(kwargs)
     source_obj = source
@@ -338,7 +345,7 @@ def parse_variable_definition(parser):
         type=expect(parser, TokenKind.COLON) and parse_type(parser),
         default_value=parse_value_literal(parser, True)
         if skip(parser, TokenKind.EQUALS)
-        else None,
+        else Undefined,
         loc=loc(parser, start),
     )
 
@@ -493,18 +500,21 @@ def parse_value_literal(parser, is_const):
         )
 
     elif token.kind == TokenKind.NAME:
+        advance(parser)
         if token.value in ("true", "false"):
-            advance(parser)
             return ast.BooleanValue(
                 value=token.value == "true", loc=loc(parser, token.start)
             )
 
-        if token.value != "null":
-            advance(parser)
-            return ast.EnumValue(
-                value=token.value, loc=loc(parser, token.start)  # type: ignore
+        if token.value == "null":
+            return ast.NullValue(
+                loc=loc(parser, token.start)  # type: ignore
             )
 
+        return ast.EnumValue(  # type: ignore
+            value=token.value, loc=loc(parser, token.start)
+        )
+
     elif token.kind == TokenKind.DOLLAR:
         if not is_const:
             return parse_variable(parser)
@@ -754,7 +764,7 @@ def parse_input_value_def(parser):
         type=expect(parser, TokenKind.COLON) and parse_type(parser),  # type: ignore
         default_value=parse_const_value(parser)
         if skip(parser, TokenKind.EQUALS)
-        else None,
+        else Undefined,
         directives=parse_directives(parser),
         loc=loc(parser, start),
     )

Diff for: graphql/language/printer.py

@@ -1,6 +1,7 @@
 import json
 
 from .visitor import Visitor, visit
+from ..utils.undefined import Undefined
 
 # Necessary for static type checking
 if False:  # flake8: noqa
@@ -45,7 +46,7 @@ def leave_OperationDefinition(self, node, *args):
 
     def leave_VariableDefinition(self, node, *args):
         # type: (Any, *Any) -> str
-        return node.variable + ": " + node.type + wrap(" = ", node.default_value)
+        return node.variable + ": " + node.type + wrap(" = ", node.default_value, is_default_value=True)
 
     def leave_SelectionSet(self, node, *args):
         # type: (Any, *Any) -> str
@@ -111,6 +112,12 @@ def leave_BooleanValue(self, node, *args):
         # type: (Any, *Any) -> str
         return json.dumps(node.value)
 
+    def leave_NullValue(self, node, *args):
+        return "null"
+
+    def leave_UndefinedValue(self, node, *args):
+        return Undefined
+
     def leave_EnumValue(self, node, *args):
         # type: (Any, *Any) -> str
         return node.value
@@ -192,7 +199,7 @@ def leave_InputValueDefinition(self, node, *args):
             node.name
             + ": "
             + node.type
-            + wrap(" = ", node.default_value)
+            + wrap(" = ", node.default_value, is_default_value=True)
             + wrap(" ", join(node.directives, " "))
         )
 
@@ -232,13 +239,14 @@ def leave_EnumValueDefinition(self, node, *args):
 
     def leave_InputObjectTypeDefinition(self, node, *args):
         # type: (Any, *Any) -> str
-        return (
+        s = (
             "input "
             + node.name
             + wrap(" ", join(node.directives, " "))
             + " "
             + block(node.fields)
         )
+        return s
 
     def leave_TypeExtensionDefinition(self, node, *args):
         # type: (Any, *Any) -> str
@@ -268,8 +276,14 @@ def block(_list):
     return "{}"
 
 
-def wrap(start, maybe_str, end=""):
-    # type: (str, Optional[str], str) -> str
+def wrap(start, maybe_str, end="", is_default_value=False):
+    # type: (str, Optional[str], str, bool) -> str
+    if is_default_value:
+        if maybe_str is Undefined:
+            return ""
+        s = "null" if maybe_str is None else maybe_str
+        return start + s + end
+
     if maybe_str:
         return start + maybe_str + end
     return ""

Diff for: graphql/language/tests/fixtures.py

@@ -53,7 +53,7 @@
 }
 
 {
-  unnamed(truthy: true, falsey: false),
+  unnamed(truthy: true, falsey: false, nullish: null),
   query
 }
 """

Diff for: graphql/language/tests/test_parser.py

@@ -101,12 +101,72 @@ def test_does_not_accept_fragments_spread_of_on():
     assert "Syntax Error GraphQL (1:9) Expected Name, found }" in excinfo.value.message
 
 
-def test_does_not_allow_null_value():
+def test_allows_null_value():
     # type: () -> None
-    with raises(GraphQLSyntaxError) as excinfo:
-        parse("{ fieldWithNullableStringInput(input: null) }")
+    parse("{ fieldWithNullableStringInput(input: null) }")
+
+
+def test_parses_null_value_to_null():
+    result = parse('{ fieldWithObjectInput(input: {a: null, b: null, c: "C", d: null}) }')
+    values = result.definitions[0].selection_set.selections[0].arguments[0].value.fields
+    expected = (
+        (u"a", ast.NullValue()),
+        (u"b", ast.NullValue()),
+        (u"c", ast.StringValue(value=u"C")),
+        (u"d", ast.NullValue()),
+    )
+    for name_value, actual in zip(expected, values):
+        assert name_value == (actual.name.value, actual.value)
+
+
+def test_parses_null_value_in_list():
+    result = parse('{ fieldWithObjectInput(input: {b: ["A", null, "C"], c: "C"}) }')
+    assert result == ast.Document(
+        definitions=[
+            ast.OperationDefinition(
+                operation="query", name=None, variable_definitions=None, directives=[],
+                selection_set=ast.SelectionSet(
+                    selections=[
+                        ast.Field(
+                            alias=None,
+                            name=ast.Name(value=u"fieldWithObjectInput"),
+                            directives=[],
+                            selection_set=None,
+                            arguments=[
+                                ast.Argument(
+                                    name=ast.Name(value=u"input"),
+                                    value=ast.ObjectValue(
+                                        fields=[
+                                            ast.ObjectField(
+                                                name=ast.Name(value=u"b"),
+                                                value=ast.ListValue(
+                                                    values=[
+                                                        ast.StringValue(value=u"A"),
+                                                        ast.NullValue(),
+                                                        ast.StringValue(value=u"C"),
+                                                    ],
+                                                ),
+                                            ),
+                                            ast.ObjectField(
+                                                name=ast.Name(value=u"c"),
+                                                value=ast.StringValue(value=u"C"),
+                                            ),
+                                        ]
+                                    ),
+                                ),
+                            ],
+                        ),
+                    ],
+                ),
+            ),
+        ],
+    )
+
 
-    assert 'Syntax Error GraphQL (1:39) Unexpected Name "null"' in excinfo.value.message
+def test_null_as_name():
+    result = parse('{ thingy(null: "stringcheese") }')
+    assert result.definitions[0].selection_set.selections[0].name.value == "thingy"
+    assert result.definitions[0].selection_set.selections[0].arguments[0].name.value == "null"
 
 
 def test_parses_multi_byte_characters():
@@ -158,6 +218,7 @@ def tesst_allows_non_keywords_anywhere_a_name_is_allowed():
         "subscription",
         "true",
         "false",
+        "null",
     ]
 
     query_template = """

Diff for: graphql/language/tests/test_printer.py

@@ -85,6 +85,14 @@ def test_correctly_prints_mutation_with_artifacts():
     )
 
 
+def test_correctly_prints_null():
+    query_ast_shorthanded = parse('{ thingy(null: "wow", name: null) }')
+    assert print_ast(query_ast_shorthanded) == """{
+  thingy(null: "wow", name: null)
+}
+"""
+
+
 def test_prints_kitchen_sink():
     # type: () -> None
     ast = parse(KITCHEN_SINK)
@@ -138,7 +146,7 @@ def test_prints_kitchen_sink():
 }
 
 {
-  unnamed(truthy: true, falsey: false)
+  unnamed(truthy: true, falsey: false, nullish: null)
   query
 }
 """