After installing the php7.1 and php7.1-fileinfo packages from edge/testing (after the changes in https://github.com/alpinelinux/aports/commit/82cd1263a39ff83b95e0f3d899ddf2e1a72181da ):

Running php -r '$finfo = new finfo(FILEINFO_MIME);' provides the following warning:

PHP Fatal error:  Uncaught Exception: finfo::finfo(): Failed to load magic database at '(null)'. in Command line code:1
Stack trace:
#0 Command line code(1): finfo->finfo(1040)
#1 {main}
  thrown in Command line code on line 1

(from redmine: issue id 6945, created on 2017-02-27, closed on 2017-04-07)