memcached extension is listed as created when it is not

Attempted to use puppet-php to install memcached.
After puppet apply, ran php -v which displayed the following error Warning: Could not match PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php/20151012/memcached.so' - /usr/lib/php/20151012/memcached.so: cannot open shared object file: No such file or directory in Unknown on line 0

attempting to run pecl install memcached manually
returned

pkg-config not found
configure: error: Please reinstall the pkg-config distribution
ERROR: `/tmp/pear/temp/memcached/configure --with-php-config=/usr/bin/php-config --with-libmemcached-dir=no' failed

Affected Puppet, Ruby, OS and module versions/distributions

• Puppet: 3.8.5
• Ruby: 2.3.1p112
• Distribution: ubuntu 16.04.2 LTS
• Module version: 4.0.0

How to reproduce (e.g Puppet code you use)

    extensions => {
      memcached => {
        provider        => 'pecl',
        header_packages => [ 'libmemcached-dev', ],
      },
    },

What are you seeing

Notice: /Stage[main]/Php/Php::Extension[memcached]/Package[memcached]/ensure: created

What behaviour did you expect instead

Notice: /Stage[main]/Php/Php::Extension[memcached] :Skipping because of failed dependencies

Output log

Any additional information you'd like to impart

Was able to successfully have puppet install memcached extension by sudo apt-get install pkgconf then re-running puppet apply.

as I see it there are two issue

1. the user should be notified if a particular extension does not compile properly
2. since pecl relies on pkg-config it would be good to check for the presence of pkg-config, and install it if necessary

Reproduce the memcached extension declaration on Ubuntu 16.04 with puppet-php 4.0.0, then inspect the PECL provider and extension dependency handling described in the issue. Done should mean missing pkg-config is handled before compilation and a failed build is reported instead of the package being marked created.