WIP - Add null support

Code is mostly copy-pasted from the PR graphql-go#536 - main difference is that I haven't copied over a couple of new tests, and that I permitted null within arrays (unanswered question in original PR, and I see no reason for it too).

language/ast/node.go

@@ -22,6 +22,7 @@ var _ Node = (*IntValue)(nil)
 var _ Node = (*FloatValue)(nil)
 var _ Node = (*StringValue)(nil)
 var _ Node = (*BooleanValue)(nil)
+var _ Node = (*NullValue)(nil)
 var _ Node = (*EnumValue)(nil)
 var _ Node = (*ListValue)(nil)
 var _ Node = (*ObjectValue)(nil)

language/ast/values.go

@@ -16,6 +16,7 @@ var _ Value = (*IntValue)(nil)
 var _ Value = (*FloatValue)(nil)
 var _ Value = (*StringValue)(nil)
 var _ Value = (*BooleanValue)(nil)
+var _ Value = (*NullValue)(nil)
 var _ Value = (*EnumValue)(nil)
 var _ Value = (*ListValue)(nil)
 var _ Value = (*ObjectValue)(nil)
@@ -172,6 +173,33 @@ func (v *BooleanValue) GetValue() interface{} {
 	return v.Value
 }
 
+type NullValue struct {
+	Kind  string
+	Loc   *Location
+	Value interface{}
+}
+
+func NewNullValue(v *NullValue) *NullValue {
+
+	return &NullValue{
+		Kind:  kinds.NullValue,
+		Loc:   v.Loc,
+		Value: v.Value,
+	}
+}
+
+func (v *NullValue) GetKind() string {
+	return v.Kind
+}
+
+func (v *NullValue) GetLoc() *Location {
+	return v.Loc
+}
+
+func (v *NullValue) GetValue() interface{} {
+	return nil
+}
+
 // EnumValue implements Node, Value
 type EnumValue struct {
 	Kind  string

language/kinds/kinds.go

@@ -23,6 +23,7 @@ const (
 	FloatValue   = "FloatValue"
 	StringValue  = "StringValue"
 	BooleanValue = "BooleanValue"
+	NullValue    = "NullValue"
 	EnumValue    = "EnumValue"
 	ListValue    = "ListValue"
 	ObjectValue  = "ObjectValue"

language/parser/parser.go

@@ -614,15 +614,23 @@ func parseValueLiteral(parser *Parser, isConst bool) (ast.Value, error) {
 				Value: value,
 				Loc:   loc(parser, token.Start),
 			}), nil
-		} else if token.Value != "null" {
+		} else if token.Value == "null" {
 			if err := advance(parser); err != nil {
 				return nil, err
 			}
-			return ast.NewEnumValue(&ast.EnumValue{
-				Value: token.Value,
+			return ast.NewNullValue(&ast.NullValue{
+				Value: nil,
 				Loc:   loc(parser, token.Start),
 			}), nil
 		}
+
+		if err := advance(parser); err != nil {
+			return nil, err
+		}
+		return ast.NewEnumValue(&ast.EnumValue{
+			Value: token.Value,
+			Loc:   loc(parser, token.Start),
+		}), nil
 	case lexer.DOLLAR:
 		if !isConst {
 			return parseVariable(parser)

language/parser/parser_test.go

@@ -183,15 +183,6 @@ func TestDoesNotAcceptFragmentsSpreadOfOn(t *testing.T) {
 	testErrorMessage(t, test)
 }
 
-func TestDoesNotAllowNullAsValue(t *testing.T) {
-	test := errorMessageTest{
-		`{ fieldWithNullableStringInput(input: null) }'`,
-		`Syntax Error GraphQL (1:39) Unexpected Name "null"`,
-		false,
-	}
-	testErrorMessage(t, test)
-}
-
 func TestParsesMultiByteCharacters_Unicode(t *testing.T) {
 
 	doc := `
@@ -367,6 +358,7 @@ func TestAllowsNonKeywordsAnywhereNameIsAllowed(t *testing.T) {
 		"subscription",
 		"true",
 		"false",
+		"null",
 	}
 	for _, keyword := range nonKeywords {
 		fragmentName := keyword

language/printer/printer.go

@@ -388,6 +388,15 @@ var printDocASTReducer = map[string]visitor.VisitFunc{
 		}
 		return visitor.ActionNoChange, nil
 	},
+	"NullValue": func(p visitor.VisitFuncParams) (string, interface{}) {
+		switch node := p.Node.(type) {
+		case *ast.NullValue:
+			return visitor.ActionUpdate, fmt.Sprintf("%v", node.Value)
+		case map[string]interface{}:
+			return visitor.ActionUpdate, getMapValueString(node, "Value")
+		}
+		return visitor.ActionNoChange, nil
+	},
 	"EnumValue": func(p visitor.VisitFuncParams) (string, interface{}) {
 		switch node := p.Node.(type) {
 		case *ast.EnumValue:

rules.go

@@ -1730,6 +1730,10 @@ func isValidLiteralValue(ttype Input, valueAST ast.Value) (bool, []string) {
 			return true, nil
 		}
 
+		if valueAST.GetKind() == kinds.NullValue {
+			return true, nil
+		}
+
 		// This function only tests literals, and assumes variables will provide
 		// values of the correct type.
 		if valueAST.GetKind() == kinds.Variable {
@@ -1742,7 +1746,7 @@ func isValidLiteralValue(ttype Input, valueAST ast.Value) (bool, []string) {
 		if e := ttype.Error(); e != nil {
 			return false, []string{e.Error()}
 		}
-		if valueAST == nil {
+		if valueAST == nil || valueAST.GetKind() == kinds.NullValue {
 			if ttype.OfType.Name() != "" {
 				return false, []string{fmt.Sprintf(`Expected "%v!", found null.`, ttype.OfType.Name())}
 			}

values.go

@@ -14,6 +14,9 @@ import (
 	"github.com/graphql-go/graphql/language/printer"
 )
 
+// Used to detect the difference between a "null" literal and not present
+type nullValue struct{}
+
 // Prepares an object map of variableValues of the correct type based on the
 // provided variable definitions and arbitrary input. If the input cannot be
 // parsed to match the variable definitions, a GraphQLError will be returned.
@@ -27,7 +30,7 @@ func getVariableValues(
 			continue
 		}
 		varName := defAST.Variable.Name.Value
-		if varValue, err := getVariableValue(schema, defAST, inputs[varName]); err != nil {
+		if varValue, err := getVariableValue(schema, defAST, getValueOrNull(inputs, varName)); err != nil {
 			return values, err
 		} else {
 			values[varName] = varValue
@@ -36,6 +39,25 @@ func getVariableValues(
 	return values, nil
 }
 
+func getValueOrNull(values map[string]interface{}, name string) interface{} {
+	if tmp, ok := values[name]; ok { // Is present
+		if tmp == nil {
+			return nullValue{} // Null value
+		} else {
+			return tmp
+		}
+	}
+	return nil // Not present
+}
+
+func addValueOrNull(values map[string]interface{}, name string, value interface{}) {
+	if _, ok := value.(nullValue); ok { // Null value
+		values[name] = nil
+	} else if !isNullish(value) { // Not present
+		values[name] = value
+	}
+}
+
 // Prepares an object map of argument values given a list of argument
 // definitions and list of argument AST nodes.
 func getArgumentValues(
@@ -60,9 +82,7 @@ func getArgumentValues(
 		if tmp = valueFromAST(value, argDef.Type, variableValues); isNullish(tmp) {
 			tmp = argDef.DefaultValue
 		}
-		if !isNullish(tmp) {
-			results[argDef.PrivateName] = tmp
-		}
+		addValueOrNull(results, argDef.PrivateName, tmp)
 	}
 	return results
 }
@@ -97,7 +117,7 @@ func getVariableValue(schema Schema, definitionAST *ast.VariableDefinition, inpu
 		}
 		return coerceValue(ttype, input), nil
 	}
-	if isNullish(input) {
+	if _, ok := input.(nullValue); ok || isNullish(input) {
 		return "", gqlerrors.NewError(
 			fmt.Sprintf(`Variable "$%v" of required type `+
 				`"%v" was not provided.`, variable.Name.Value, printer.Print(definitionAST.Type)),
@@ -134,6 +154,11 @@ func coerceValue(ttype Input, value interface{}) interface{} {
 	if isNullish(value) {
 		return nil
 	}
+
+	if _, ok := value.(nullValue); ok {
+		return nullValue{}
+	}
+
 	switch ttype := ttype.(type) {
 	case *NonNull:
 		return coerceValue(ttype.OfType, value)
@@ -156,13 +181,11 @@ func coerceValue(ttype Input, value interface{}) interface{} {
 		}
 
 		for name, field := range ttype.Fields() {
-			fieldValue := coerceValue(field.Type, valueMap[name])
+			fieldValue := coerceValue(field.Type, getValueOrNull(valueMap, name))
 			if isNullish(fieldValue) {
 				fieldValue = field.DefaultValue
 			}
-			if !isNullish(fieldValue) {
-				obj[name] = fieldValue
-			}
+			addValueOrNull(obj, name, fieldValue)
 		}
 		return obj
 	case *Scalar:
@@ -212,7 +235,7 @@ func typeFromAST(schema Schema, inputTypeAST ast.Type) (Type, error) {
 // accepted for that type. This is primarily useful for validating the
 // runtime values of query variables.
 func isValidInputValue(value interface{}, ttype Input) (bool, []string) {
-	if isNullish(value) {
+	if _, ok := value.(nullValue); ok || isNullish(value) {
 		if ttype, ok := ttype.(*NonNull); ok {
 			if ttype.OfType.Name() != "" {
 				return false, []string{fmt.Sprintf(`Expected "%v!", found null.`, ttype.OfType.Name())}
@@ -233,9 +256,14 @@ func isValidInputValue(value interface{}, ttype Input) (bool, []string) {
 			messagesReduce := []string{}
 			for i := 0; i < valType.Len(); i++ {
 				val := valType.Index(i).Interface()
-				_, messages := isValidInputValue(val, ttype.OfType)
-				for idx, message := range messages {
-					messagesReduce = append(messagesReduce, fmt.Sprintf(`In element #%v: %v`, idx+1, message))
+				var messages []string
+				if _, ok := val.(nullValue); ok {
+					messages = []string{"Unexpected null value."}
+				} else {
+					_, messages = isValidInputValue(val, ttype.OfType)
+				}
+				for _, message := range messages {
+					messagesReduce = append(messagesReduce, fmt.Sprintf(`In element #%v: %v`, i+1, message))
 				}
 			}
 			return (len(messagesReduce) == 0), messagesReduce
@@ -352,6 +380,11 @@ func valueFromAST(valueAST ast.Value, ttype Input, variables map[string]interfac
 	if valueAST == nil {
 		return nil
 	}
+
+	if valueAST.GetKind() == kinds.NullValue {
+		return nullValue{}
+	}
+
 	// precedence: value > type
 	if valueAST, ok := valueAST.(*ast.Variable); ok {
 		if valueAST.Name == nil || variables == nil {
@@ -398,9 +431,7 @@ func valueFromAST(valueAST ast.Value, ttype Input, variables map[string]interfac
 			} else {
 				value = field.DefaultValue
 			}
-			if !isNullish(value) {
-				obj[name] = value
-			}
+			addValueOrNull(obj, name, value)
 		}
 		return obj
 	case *Scalar:

variables_test.go

@@ -67,7 +67,7 @@ var testNestedInputObject *graphql.InputObject = graphql.NewInputObject(graphql.
 
 func inputResolved(p graphql.ResolveParams) (interface{}, error) {
 	input, ok := p.Args["input"]
-	if !ok {
+	if !ok || input == nil {
 		return nil, nil
 	}
 	b, err := json.Marshal(input)
@@ -1188,7 +1188,7 @@ func TestVariables_ListsAndNullability_DoesNotAllowListOfNonNullsToContainNull(t
 			{
 				Message: `Variable "$input" got invalid value ` +
 					`["A",null,"B"].` +
-					"\nIn element #1: Expected \"String!\", found null.",
+					"\nIn element #2: Expected \"String!\", found null.",
 				Locations: []location.SourceLocation{
 					{
 						Line: 2, Column: 17,
@@ -1290,7 +1290,7 @@ func TestVariables_ListsAndNullability_DoesNotAllowNonNullListOfNonNullsToContai
 			{
 				Message: `Variable "$input" got invalid value ` +
 					`["A",null,"B"].` +
-					"\nIn element #1: Expected \"String!\", found null.",
+					"\nIn element #2: Expected \"String!\", found null.",
 				Locations: []location.SourceLocation{
 					{
 						Line: 2, Column: 17,