(PHP 5 >= 5.3.0, PHP 7, PECL phar >= 2.0.0)
Phar::isWritable — Returns true if the phar archive can be modified
This method returns TRUE if phar.readonly is 0,
and the actual phar archive on disk is not read-only.
No parameters.
Returns TRUE if the phar archive can be modified
It might be not expected, but this function will return true if the file does not exist yet even if the directory is read-only. Tested on PHP 5.3.0 RC 1.
I have buffering on and when I call stopBuffering() then the "failed to open stream: Permission denied" PharException will be thrown.