Make libraries a dependency and deprecate vendor/arc

This is due to the awkward way the ARC2 location is set, which I believe was carried over from the D6 RDF module. If libraries.module is enabled, RDFx will assume that ARC2 is installed there.

From the first lines in rdfx.module:

if (module_exists('libraries')) {
  define('RDF_ARC2_PATH', libraries_get_path('arc'));
}
else {
  define('RDF_ARC2_PATH', drupal_get_path('module', 'rdfx') . '/vendor/arc');
}

We can definitely improve this.

I think we should strongly encourage the use of Libraries, but not make it a dependency. Maybe the README and project page should include something about it?

In the issue #1136944: ARC2 is a dependency, but not handled as such scor indicates that SPARQL should be dependent on RDFx. Anything that depends on RDFx will have access to the full set of ARC2 features (assuming ARC is installed properly). Are there other D7 modules using ARC that don't depend on RDFx?

Also, the original issue here may end up fixed by #1124580: Add extra measures to prevent errors when ARC library cannot be found.

For those new to this issue, what needs to happen here is to remove any trace of vendor/arc and download the ARC2 lib to the libraries location. All the existing libraries code is good, it's just a matter of removing the conditions and using it all the time.

Hi. Here's a patch theat addresses the issue and also takes into account people installing ARC2 in the standard php library include path.

+++ b/rdfx.module
@@ -7,22 +7,17 @@
+    $path = DRUPAL_ROOT . '/'. drupal_get_path('module', 'rdfx') . '/vendor';
+    if (module_exists('libraries')) {
+      $path .= PATH_SEPARATOR . DRUPAL_ROOT . '/' . libraries_get_path('ARC2');

I'm not sure you want .= in the last line, but rather =?

@Stefan: what do you suggest instead of making libraries a dependency and avoiding the double location confusion then?

@scor: I the last line you quoted above I want to add all the possible locations to the include path, so it is ".=". This makes it possible to put the library in either location. You can also have the library in the standard include path, e.g. /usr/share/php/arc or something like that. In this patch I replace the vendor location with sites/all/libraries.

Ok. We should not introduce new ways of loading external libraries here. I have added the dependency on libraries and will add patches there if the include_path approach is beneficial in general.