[Issue 18789] New: std.stdio messes up UTF conversions on output

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18789

          Issue ID: 18789
           Summary: std.stdio messes up UTF conversions on output
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: ag0aep6g at gmail.com

----
import std.stdio;
void main()
{   
    // converting to char
    {
        auto f = File("test.txt", "w");
        f.writeln("\U0001F608"w); // UTFException
    }

    // converting to wchar_t
    {
        auto f = File("test.txt", "w,ccs=UTF16LE");
        // from char
        f.writeln("ö"); // writes garbage
        f.writeln("\U0001F608"); // ditto
        // from wchar
        f.writeln("\U0001F608"w); // leads to ErrnoException
    }
}
----

PR follows.

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