https://issues.dlang.org/show_bug.cgi?id=17556

          Issue ID: 17556
           Summary: std.json encodes non-BMP characters incorrectly with
                    JSONOptions.escapeNonAsciiChars
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P3
         Component: phobos
          Assignee: nobody@puremagic.com
          Reporter: dlang-bugzilla@thecybershadow.net

/////////////////// test.d ///////////////////
import std.json;
import std.stdio;

void main()
{
    auto v = JSONValue("\U0001D11E");
    writeln(toJSON(v, false,
            JSONOptions.escapeNonAsciiChars));
}
//////////////////////////////////////////////

Above program prints "\uD11E", which is not the correct character.

Non-BMP characters should be encoded as a pair of escaped UTF-16 surrogate pairs, as per RFC 4627.

See also issue 5904.

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