parsePathDataFast() does not write any warnings. It can indicate errors to the caller only by returning a std::nullopt to which the caller can then react by writing a warning. This is not exact enough to handle the various possible cases:

• When the function returns std::nullopt, no warning should be written if dataStr is empty or "none".
• When the function returns an actual QPainterPath, it should still issue a warning if the contents of dataStr were partially invalid.

It seems like parsePathDataFast() itself - and not the caller - should decide on when to log a warning.