fix DateTime literal parsing

scalars.go

@@ -561,7 +561,7 @@ var DateTime = NewScalar(ScalarConfig{
 	ParseLiteral: func(valueAST ast.Value) interface{} {
 		switch valueAST := valueAST.(type) {
 		case *ast.StringValue:
-			return valueAST.Value
+			return unserializeDateTime(valueAST.Value)
 		}
 		return nil
 	},

scalars_parse_test.go

@@ -0,0 +1,54 @@
+package graphql_test
+
+import (
+	"reflect"
+	"testing"
+	"time"
+
+	"github.com/graphql-go/graphql"
+	"github.com/graphql-go/graphql/language/ast"
+)
+
+func TestTypeSystem_Scalar_ParseValueOutputDateTime(t *testing.T) {
+	t1, _ := time.Parse(time.RFC3339, "2017-07-23T03:46:56.647Z")
+	tests := []dateTimeSerializationTest{
+		{nil, nil},
+		{"", nil},
+		{(*string)(nil), nil},
+		{"2017-07-23", nil},
+		{"2017-07-23T03:46:56.647Z", t1},
+	}
+	for _, test := range tests {
+		val := graphql.DateTime.ParseValue(test.Value)
+		if val != test.Expected {
+			reflectedValue := reflect.ValueOf(test.Value)
+			t.Fatalf("failed DateTime.ParseValue(%v(%v)), expected: %v, got %v", reflectedValue.Type(), test.Value, test.Expected, val)
+		}
+	}
+}
+
+func TestTypeSystem_Scalar_ParseLiteralOutputDateTime(t *testing.T) {
+	t1, _ := time.Parse(time.RFC3339, "2017-07-23T03:46:56.647Z")
+	for name, testCase := range map[string]struct {
+		Literal  ast.Value
+		Expected interface{}
+	}{
+		"String": {
+			Literal: &ast.StringValue{
+				Value: "2017-07-23T03:46:56.647Z",
+			},
+			Expected: t1,
+		},
+		"NotAString": {
+			Literal:  &ast.IntValue{},
+			Expected: nil,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			parsed := graphql.DateTime.ParseLiteral(testCase.Literal)
+			if parsed != testCase.Expected {
+				t.Fatalf("failed DateTime.ParseLiteral(%T(%v)), expected: %v, got %v", testCase.Literal, testCase.Literal, parsed, testCase.Expected)
+			}
+		})
+	}
+}