PHP extension directory not consistent with PECL installed extensions

[deeky666]

I ran into a problem when trying to install PHP + PECL extensions (via phpPackages package).
When PHP compiles, it installs extensions configured during build into a default directory like lib/php/extensions/no-debug-zts-20131226 which differs for each PHP version and compile configurations (like ZTS support).
When installing PECL extensions via phpPackages ontop of PHP, they are installed into a fixed directory lib/php/extensions which makes it impossible to load those via php.ini (without knowing the absolute path) as PHP expects them to find in lib/php/extensions/no-debug-zts-20131226.
In scenarios where you define your php.ini outside of nix context, it is impossible to load the PECL extensions.

I wonder if a consistent extension directory for both PHP and PECL extensions could be established. Maybe the PHP package could set the EXTENSION_DIR (see here) environment variable to lib/php/extensions before configure like it is done in the PECL builder.

That would make it much easier to configure PHP extensions.

See my profile to get an impression:

root@a4a1c46b4e9a:/# ls -ali /nix/var/nix/profiles/zosch/lib/php/extensions/                      
total 24
13778796 dr-xr-xr-x 2 root nixbld 4096 Jan  1  1970 .
13778778 dr-xr-xr-x 3 root nixbld 4096 Jan  1  1970 ..
13778797 lrwxrwxrwx 1 root nixbld   85 Jan  1  1970 apcu.so -> /nix/store/xwiamby7pbnx8zmwpa68rqbmgwal7v97-php-apcu-4.0.7/lib/php/extensions/apcu.so
13778798 lrwxrwxrwx 1 root nixbld   95 Jan  1  1970 no-debug-zts-20131226 -> /nix/store/5bv024pmkg4p6kx49b5g3mqycbsfyz6w-php-5.6.15/lib/php/extensions/no-debug-zts-20131226
13778799 lrwxrwxrwx 1 root nixbld   94 Jan  1  1970 pthreads.so -> /nix/store/mmi3rlnqwrjn283rcq4w79jgbvnzs0lm-php-pthreads-2.0.10/lib/php/extensions/pthreads.so
13778800 lrwxrwxrwx 1 root nixbld   89 Jan  1  1970 xdebug.so -> /nix/store/dwbp7avnlcask7dd3a9ywhgis4y3hm2g-php-xdebug-2.3.1/lib/php/extensions/xdebug.so

root@a4a1c46b4e9a:/# ls -ali /nix/var/nix/profiles/zosch/lib/php/extensions/no-debug-zts-20131226/
total 444
13774978 dr-xr-xr-x 2 root nixbld   4096 Jan  1  1970 .
13774899 dr-xr-xr-x 3 root nixbld   4096 Jan  1  1970 ..
13778726 -r-xr-xr-x 1 root nixbld 268300 Jan  1  1970 opcache.a
13775037 -r-xr-xr-x 1 root nixbld 175298 Jan  1  1970 opcache.so

/cc @shlevy @globin