[SofaPython3] Restore the plugins automatic registering of path to python libraries.

When we load a c++ plugin it may be packaged with additional python files
(examples, libraries, or per plugin binding). These files should be visible from the python environment.

This is done by the added code that scans the plugin's directory and register any path matching the following patterns:
pluginName/lib/site-packages
pluginName/lib/python3/site-packages

This behavior was the implemented in the previous version of SofaPython and proved to be useful.

Author: damienmarchal

Plugin/src/SofaPython3/PythonEnvironment.cpp

@@ -52,34 +52,37 @@ along with sofaqtquick. If not, see <http://www.gnu.org/licenses/>.
 #include <dlfcn.h>
 #endif
 
+#include <sofa/helper/system/PluginManager.h>
+using sofa::helper::system::PluginManager;
+using sofa::helper::system::Plugin;
+
 #include <sofa/helper/system/FileRepository.h>
-#include <sofa/helper/system/FileSystem.h>
 #include <sofa/helper/system/SetDirectory.h>
+#include <sofa/helper/system/FileSystem.h>
+using sofa::helper::system::FileSystem;
 
 #include <sofa/helper/Utils.h>
+using sofa::helper::Utils;
+
 #include <sofa/helper/StringUtils.h>
 using sofa::helper::getAStringCopy ;
 
-using sofa::helper::system::FileSystem;
-using sofa::helper::Utils;
-
 #include <SofaPython3/PythonEnvironment.h>
 
 #include <sofa/helper/logging/Messaging.h>
-MSG_REGISTER_CLASS(sofapython3::PythonEnvironment, "SofaPython3::PythonEnvironment")
 
 #include <sofa/simulation/SceneLoaderFactory.h>
 using sofa::simulation::SceneLoaderFactory;
 
-//#include "Python.h"
-
 #include <pybind11/embed.h>
 #include <pybind11/eval.h>
 namespace py = pybind11;
 
 #include "SceneLoaderPY3.h"
 using sofapython3::SceneLoaderPY3;
 
+MSG_REGISTER_CLASS(sofapython3::PythonEnvironment, "SofaPython3::PythonEnvironment")
+
 namespace sofapython3
 {
 
@@ -248,6 +251,8 @@ void PythonEnvironment::Init()
         }
     }
 
+    addPythonModulePathsForPluginsByName("SofaPython3");
+
     getStaticData()->m_sofamodule = py::module::import("Sofa");
 
 
@@ -318,23 +323,64 @@ void PythonEnvironment::addPythonModulePathsFromConfigFile(const std::string& pa
 
 void PythonEnvironment::addPythonModulePathsForPlugins(const std::string& pluginsDirectory)
 {
+    bool added = false;
+
+    std::vector<std::string> pythonDirs = {
+        pluginsDirectory,
+        pluginsDirectory + "/lib",
+        pluginsDirectory + "/python3"
+    };
+
+    /// Iterate in the pluginsDirectory and add each sub directory with a 'python' name
+    /// this is mostly for in-tree builds.
     std::vector<std::string> files;
     FileSystem::listDirectory(pluginsDirectory, files);
-
     for (std::vector<std::string>::iterator i = files.begin(); i != files.end(); ++i)
     {
-        const std::string pluginPath = pluginsDirectory + "/" + *i;
-        if (FileSystem::exists(pluginPath) && FileSystem::isDirectory(pluginPath))
+        const std::string pluginSubdir = pluginsDirectory + "/" + *i;
+        if (FileSystem::exists(pluginSubdir) && FileSystem::isDirectory(pluginSubdir))
         {
-            const std::string pythonDir = pluginPath + "/python";
-            if (FileSystem::exists(pythonDir) && FileSystem::isDirectory(pythonDir))
-            {
-                addPythonModulePath(pythonDir);
-            }
+            pythonDirs.push_back(pluginSubdir + "/python3");
         }
     }
+
+    /// For each of the directories in pythonDirs, search for a site-packages entry
+    for(std::string pythonDir : pythonDirs)
+    {
+        // Search for a subdir "site-packages"
+        if (FileSystem::exists(pythonDir+"/site-packages") && FileSystem::isDirectory(pythonDir+"/site-packages"))
+        {
+            addPythonModulePath(pythonDir+"/site-packages");
+            added = true;
+        }
+    }
+
+    if(!added)
+    {
+        msg_warning("PythonEnvironment") << "No python dir found in " << pluginsDirectory;
+    }
 }
 
+void PythonEnvironment::addPythonModulePathsForPluginsByName(const std::string& pluginName)
+{
+    std::map<std::string, Plugin>& map = PluginManager::getInstance().getPluginMap();
+    for( const auto& elem : map)
+    {
+        Plugin p = elem.second;
+        if ( p.getModuleName() == pluginName )
+        {
+            std::string pluginLibraryPath = elem.first;
+            // moduleRoot should be 2 levels above the library (plugin_name/lib/plugin_name.so)
+            std::string moduleRoot = FileSystem::getParentDirectory(FileSystem::getParentDirectory(pluginLibraryPath));
+
+            addPythonModulePathsForPlugins(moduleRoot);
+            return;
+        }
+    }
+    msg_warning("PythonEnvironment") << pluginName << " not found in PluginManager's map.";
+}
+
+
 // some basic RAII stuff to handle init/termination cleanly
 namespace
 {

Plugin/src/SofaPython3/PythonEnvironment.h

@@ -94,7 +94,8 @@ class SOFAPYTHON3_API PythonEnvironment
 
     /// Add all the directories matching <pluginsDirectory>/*/python to sys.path
     /// NB: can also be used for projects <projectDirectory>/*/python
-    static void addPythonModulePathsForPlugins(const std::string& pluginsDirectory);
+    static void addPythonModulePathsForPlugins(const std::string& pluginsDirectory);    
+    static void addPythonModulePathsForPluginsByName(const std::string& pluginName);
 
     /// set the content of sys.argv.
     static void setArguments(const std::string& filename,