Allow trailing comma in arrays if dropped null placeholders are not allowed

Author: kimsey0

src/lib_json/json_reader.cpp

@@ -502,15 +502,16 @@ bool Reader::readArray(Token& token) {
   Value init(arrayValue);
   currentValue().swapPayload(init);
   currentValue().setOffsetStart(token.start_ - begin_);
-  skipSpaces();
-  if (current_ != end_ && *current_ == ']') // empty array
-  {
-    Token endArray;
-    readToken(endArray);
-    return true;
-  }
   int index = 0;
   for (;;) {
+    skipSpaces();
+    if (current_ != end_ && *current_ == ']' && (index == 0 || (features_.allowTrailingCommas_ && !features_.allowDroppedNullPlaceholders_))) // empty array or trailing comma
+    {
+      Token endArray;
+      readToken(endArray);
+      return true;
+    }
+
     Value& value = currentValue()[index++];
     nodes_.push(&value);
     bool ok = readValue();
@@ -1477,15 +1478,15 @@ bool OurReader::readArray(Token& token) {
   Value init(arrayValue);
   currentValue().swapPayload(init);
   currentValue().setOffsetStart(token.start_ - begin_);
-  skipSpaces();
-  if (current_ != end_ && *current_ == ']') // empty array
-  {
-    Token endArray;
-    readToken(endArray);
-    return true;
-  }
   int index = 0;
   for (;;) {
+    skipSpaces();
+    if (current_ != end_ && *current_ == ']' && (index == 0 || (features_.allowTrailingCommas_ && !features_.allowDroppedNullPlaceholders_))) // empty array or trailing comma
+    {
+      Token endArray;
+      readToken(endArray);
+      return true;
+    }
     Value& value = currentValue()[index++];
     nodes_.push(&value);
     bool ok = readValue();

test/data/fail_test_array_02.json

@@ -0,0 +1 @@
+[1,,]

test/data/test_array_08.expected

@@ -0,0 +1,2 @@
+.=[]
+.[0]=1

test/data/test_array_08.json

@@ -0,0 +1 @@
+[1,]