Added optional support for trailing commas

This adds kParseTrailingCommasFlag to allow a trailing comma at the
end of maps and arrays. This is part of issue #36, adding optional
support for relaxed JSON syntax.

doc/dom.md

@@ -116,6 +116,7 @@ Parse flags                   | Meaning
 `kParseStopWhenDoneFlag`      | After parsing a complete JSON root from stream, stop further processing the rest of stream. When this flag is used, parser will not generate `kParseErrorDocumentRootNotSingular` error. Using this flag for parsing multiple JSONs in the same stream.
 `kParseFullPrecisionFlag`     | Parse number in full precision (slower). If this flag is not set, the normal precision (faster) is used. Normal precision has maximum 3 [ULP](http://en.wikipedia.org/wiki/Unit_in_the_last_place) error.
 `kParseCommentsFlag`          | Allow one-line `// ...` and multi-line `/* ... */` comments (relaxed JSON syntax).
+`kParseTrailingCommasFlag`    | Allow trailing commas at the end of objects and arrays (relaxed JSON syntax).
 
 By using a non-type template parameter, instead of a function parameter, C++ compiler can generate code which is optimized for specified combinations, improving speed, and reducing code size (if only using a single specialization). The downside is the flags needed to be determined in compile-time.
 

include/rapidjson/reader.h

@@ -149,6 +149,7 @@ enum ParseFlag {
     kParseFullPrecisionFlag = 16,   //!< Parse number in full precision (but slower).
     kParseCommentsFlag = 32,        //!< Allow one-line (//) and multi-line (/**/) comments.
     kParseNumbersAsStringsFlag = 64,    //!< Parse all numbers (ints/doubles) as strings.
+    kParseTrailingCommasFlag = 128, //!< Allow trailing commas at the end of objects and arrays.
     kParseDefaultFlags = RAPIDJSON_PARSE_DEFAULT_FLAGS  //!< Default parse flags. Can be customized by defining RAPIDJSON_PARSE_DEFAULT_FLAGS
 };
 
@@ -636,6 +637,15 @@ private:
                     RAPIDJSON_PARSE_ERROR(kParseErrorObjectMissCommaOrCurlyBracket, is.Tell());
                     break;
             }
+
+            if (parseFlags & kParseTrailingCommasFlag) {
+                if (is.Peek() == '}') {
+                    is.Take();
+                    if (RAPIDJSON_UNLIKELY(!handler.EndObject(memberCount)))
+                        RAPIDJSON_PARSE_ERROR(kParseErrorTermination, is.Tell());
+                    return;
+                }
+            }
         }
     }
 
@@ -676,6 +686,15 @@ private:
             }
             else
                 RAPIDJSON_PARSE_ERROR(kParseErrorArrayMissCommaOrSquareBracket, is.Tell());
+
+            if (parseFlags & kParseTrailingCommasFlag) {
+                if (is.Peek() == ']') {
+                    is.Take();
+                    if (RAPIDJSON_UNLIKELY(!handler.EndArray(elementCount)))
+                        RAPIDJSON_PARSE_ERROR(kParseErrorTermination, is.Tell());
+                    return;
+                }
+            }
         }
     }
 

test/unittest/readertest.cpp

@@ -778,6 +778,10 @@ TEST(Reader, ParseArray_Error) {
     TEST_ARRAY_ERROR(kParseErrorArrayMissCommaOrSquareBracket, "[1}", 2);
     TEST_ARRAY_ERROR(kParseErrorArrayMissCommaOrSquareBracket, "[1 2]", 3);
 
+    // Array cannot have a trailing comma (without kParseTrailingCommasFlag);
+    // a value must follow a comma
+    TEST_ARRAY_ERROR(kParseErrorValueInvalid, "[1,]", 3);
+
 #undef TEST_ARRAY_ERROR
 }
 
@@ -978,6 +982,10 @@ TEST(Reader, ParseObject_Error) {
     // Must be a comma or '}' after an object member
     TEST_ERROR(kParseErrorObjectMissCommaOrCurlyBracket, "{\"a\":1]", 6);
 
+    // Object cannot have a trailing comma (without kParseTrailingCommasFlag);
+    // an object member name must follow a comma
+    TEST_ERROR(kParseErrorObjectMissName, "{\"a\":1,}", 7);
+
     // This tests that MemoryStream is checking the length in Peek().
     {
         MemoryStream ms("{\"a\"", 1);
@@ -1552,6 +1560,35 @@ TEST(Reader, NumbersAsStrings) {
 	}
 }
 
+TEST(Reader, TrailingCommas) {
+    {
+        // trailing array comma
+        StringStream s("[1,2,3,]");
+        ParseArrayHandler<3> h;
+        Reader reader;
+        EXPECT_TRUE(reader.Parse<kParseTrailingCommasFlag>(s, h));
+        EXPECT_EQ(5u, h.step_);
+    }
+    {
+        // trailing object comma
+        const char* json = "{ \"hello\" : \"world\", \"t\" : true , \"f\" : false, \"n\": null, \"i\":123, \"pi\": 3.1416, \"a\":[1, 2, 3],}";
+        StringStream s(json);
+        ParseObjectHandler h;
+        Reader reader;
+        EXPECT_TRUE(reader.Parse<kParseTrailingCommasFlag>(s, h));
+        EXPECT_EQ(20u, h.step_);
+    }
+    {
+        // trailing object and array commas with whitespace
+        const char* json = "{ \"hello\" : \"world\", \"t\" : true , \"f\" : false, \"n\": null, \"i\":123, \"pi\": 3.1416, \"a\":[1, 2, 3\n,\n]\n,\n } ";
+        StringStream s(json);
+        ParseObjectHandler h;
+        Reader reader;
+        EXPECT_TRUE(reader.Parse<kParseTrailingCommasFlag>(s, h));
+        EXPECT_EQ(20u, h.step_);
+    }
+}
+
 #ifdef __GNUC__
 RAPIDJSON_DIAG_POP
 #endif