Drupal Settings Compile
You should be able to treat the Drupal configuration represented in settings.php like a simple dictionary that can be serialized in any format that can represent a dictionary, because that's what settings.php actually is. This makes it simple to change the settings without knowing php and even without logging onto the server or making any git commits. You would want to allow this because your application will likely need to exist in several different environments at any arbitrary commit in its history.
An alternate strategy would be to version a settings.php that sets the
configuration variables according to Environment Variables fetched with
getenv(). If you have control over the visibility of Environment Variables to
the running php process, then that approach is preferable.
Install this project with composer.
examples/config.yml and witness the resulting
settings.php when invoking
vendor/bin/settings_compile vendor/winmillwill/settings_compile/examples/config.yml settings.php
or you could even do this:
vendor/bin/settings_compile https://raw.githubusercontent.com/winmillwill/settings_compile/master/examples/config.yml settings.php
The command simply takes a path to a correctly formatted yaml file and the desired path at which to write the resulting settings.php file.
You can see this stated fairly plainly in Drupal\Settings\Schema but the gist is that you address the globals that are available for modification in settings.php by using the settings key, hence your databases hash would start like this:
drupal: ... settings: databases: ...
and the keys you can set under settings is limited to this list:
You can require your composer autoloader (or any other php file) like this (for 2.0.x):
drupal: ... include: require: - $DRUPAL_ROOT/relative/path/to/vendor/autoload.php
This works because all values are naively quoted in 2.0.x.
You can specify the full path without aid of the
DRUPAL_ROOT macro, though
that would require whoever edits the yaml file to know the full path to the
Drupal application on whatever server.
You can additionally effect ini settings like this:
drupal: ... ini: xdebug.show_exception_trace: 1
Starting with 2.1.1, you can disable quoting for your value by prefixing with
%, which gives you full access to php:
drupal: ... include: require: - %DRUPAL_ROOT . '/relative/path/to/vendor/autoload.php'
Similarly, any value starting with a
$ is also naively left untreated.
Alternate Strategy with Environment Variables
You can also use the
% escaping to make a yaml file that can very easily model
your config as something that is aware of its environment:
drupal: ... settings: db_url: %getenv('DRUPAL_DB_URL')
This makes setting up for your PAAS simple, though it does begin to beg the question as to whether you gain anything by using yaml instead of just versioning the php file and letting another system manage setting the environment variables, as described above in Motivation.