//////////////// test.d /////////////// import std.string; void main() { assert("%02d"d.format(1) == "01"d); } /////////////////////////////////////// Code throws "Incorrect format specifier: 02d" exception at runtime. Introduced in https://github.com/D-Programming-Language/phobos/pull/4427.
Same issue with wstring format
*** This issue has been marked as a duplicate of issue 16661 ***