Fix #44: trailing comma when printing null value

Author: swolchok

JsonVisitor.cpp

@@ -26,12 +26,15 @@ void JsonVisitor::printLocation(const yy::location &location)
        << ",\"end\":" << location.end.column  << '}';
 }
 
-void JsonVisitor::startPrintingNode(const char *kind, const yy::location &location) {
+void JsonVisitor::startPrintingNodeWithoutTrailingComma(const char *kind, const yy::location &location) {
   out_.str("");
   out_ << "{\"kind\":\"" << kind << "\",\"loc\":";
   printLocation(location);
+}
+
+void JsonVisitor::startPrintingNode(const char *kind, const yy::location &location) {
+  startPrintingNodeWithoutTrailingComma(kind, location);
   out_ << ',';
-  return;
 }
 
 void JsonVisitor::printChildList(
@@ -349,7 +352,7 @@ void JsonVisitor::endVisitEnumValue(const EnumValue &enumValue) {
 }
 
 void JsonVisitor::endVisitNullValue(const NullValue &nullValue) {
-  startPrintingNode("NullValue", nullValue.getLocation());
+  startPrintingNodeWithoutTrailingComma("NullValue", nullValue.getLocation());
   out_ << '}';
   printed_.back().emplace_back(out_.str());
 }

JsonVisitor.h

@@ -34,6 +34,10 @@ class JsonVisitor : public AstVisitor {
 
   // Print the opening of a new JSON dictionary, the node kind, and
   // the node location.
+  void startPrintingNodeWithoutTrailingComma(const char *kind, const yy::location &location);
+
+  // Like startPrintingNodeWithoutTrailingComma, but adds a trailing
+  // comma for convenience.
   void startPrintingNode(const char *kind, const yy::location &location);
 
   void printLocation(const yy::location &location);

test/CMakeLists.txt

@@ -6,7 +6,7 @@ INCLUDE_DIRECTORIES(${gtest_SOURCE_DIR}/include ${gtest_SOURCE_DIR})
 
 FILE(COPY valgrind.supp DESTINATION .)
 
-ADD_EXECUTABLE(runTests ParserTests.cpp BuildCAPI.c)
+ADD_EXECUTABLE(runTests ParserTests.cpp JsonVisitorTests.cpp BuildCAPI.c)
 
 TARGET_LINK_LIBRARIES(runTests gtest gtest_main)
 

test/JsonVisitorTests.cpp

@@ -0,0 +1,28 @@
+/**
+ * Copyright (c) 2016, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#include <gtest/gtest.h>
+
+#include "Ast.h"
+#include "GraphQLParser.h"
+#include "c/GraphQLAstToJSON.h"
+
+using namespace facebook::graphql;
+using namespace facebook::graphql::ast;
+
+TEST(JsonVisitorTests, NullValueEmitsValidJSONWithoutTrailingComma) {
+  const char *error = nullptr;
+  auto AST = parseString("{field(arg: null)}", &error);
+  ASSERT_STREQ(nullptr, error) << "GraphQL parser error: " << error;
+  const char *json = graphql_ast_to_json((const struct GraphQLAstNode *)AST.get());
+
+  EXPECT_STREQ(
+    json,
+    "{\"kind\":\"Document\",\"loc\":{\"start\":1,\"end\":19},\"definitions\":[{\"kind\":\"OperationDefinition\",\"loc\":{\"start\":1,\"end\":19},\"operation\":\"query\",\"name\": null,\"variableDefinitions\":null,\"directives\":null,\"selectionSet\":{\"kind\":\"SelectionSet\",\"loc\":{\"start\":1,\"end\":19},\"selections\":[{\"kind\":\"Field\",\"loc\":{\"start\":2,\"end\":18},\"alias\":null,\"name\":{\"kind\":\"Name\",\"loc\":{\"start\":2,\"end\":7},\"value\":\"field\"},\"arguments\":[{\"kind\":\"Argument\",\"loc\":{\"start\":8,\"end\":17},\"name\":{\"kind\":\"Name\",\"loc\":{\"start\":8,\"end\":11},\"value\":\"arg\"},\"value\":{\"kind\":\"NullValue\",\"loc\":{\"start\":13,\"end\":17}}}],\"directives\":null,\"selectionSet\":null}]}}]}");
+}