Always true condition.

    for (int index = 0; index < size && !isMultiLine; ++index) 
In addition to dead code, in the above if condition checking to !isMultiLine is of no use as it will be always true and hence "for" depends only on condition [index < size.]
The mentioned test case works fine in this case also.

Author: renu555

src/lib_json/json_writer.cpp

@@ -341,7 +341,7 @@ bool StyledWriter::isMultineArray(const Value &value) {
     childValues_.reserve(size);
     addChildValues_ = true;
     int lineLength = 4 + (size - 1) * 2; // '[ ' + ', '*n + ' ]'
-    for (int index = 0; index < size && !isMultiLine; ++index) {
+    for (int index = 0; index < size; ++index) {
       writeValue(value[index]);
       lineLength += int(childValues_[index].length());
     }
@@ -564,7 +564,7 @@ bool StyledStreamWriter::isMultineArray(const Value &value) {
     childValues_.reserve(size);
     addChildValues_ = true;
     int lineLength = 4 + (size - 1) * 2; // '[ ' + ', '*n + ' ]'
-    for (int index = 0; index < size && !isMultiLine; ++index) {
+    for (int index = 0; index < size; ++index) {
       writeValue(value[index]);
       lineLength += int(childValues_[index].length());
     }