Search the installation data directory (#693)

That allows the logic to work on non-FHS distros like NixOS

CMakeLists.txt

@@ -97,6 +97,11 @@ option(ALSOFT_UPDATE_BUILD_VERSION "Update git build version info" ON)
 
 option(ALSOFT_EAX "Enable legacy EAX extensions" ${WIN32})
 
+option(ALSOFT_SEARCH_INSTALL_DATADIR "Search the installation data directory" OFF)
+if(ALSOFT_SEARCH_INSTALL_DATADIR)
+    set(ALSOFT_INSTALL_DATADIR ${CMAKE_INSTALL_FULL_DATADIR})
+endif()
+
 if(DEFINED SHARE_INSTALL_DIR)
     message(WARNING "SHARE_INSTALL_DIR is deprecated.  Use the variables provided by the GNUInstallDirs module instead")
     set(CMAKE_INSTALL_DATADIR "${SHARE_INSTALL_DIR}")

config.h.in

@@ -114,3 +114,6 @@
 
 /* Define if we have pthread_set_name_np() */
 #cmakedefine HAVE_PTHREAD_SET_NAME_NP
+
+/* Define the installation data directory */
+#cmakedefine ALSOFT_INSTALL_DATADIR "@ALSOFT_INSTALL_DATADIR@"

core/helpers.cpp

@@ -408,6 +408,20 @@ al::vector<std::string> SearchDataFiles(const char *ext, const char *subdir)
         DirectorySearch(path.c_str(), ext, &results);
     }
 
+#ifdef ALSOFT_INSTALL_DATADIR
+    // Search the installation data directory
+    {
+        std::string path{ALSOFT_INSTALL_DATADIR};
+        if(!path.empty())
+        {
+            if(path.back() != '/')
+                path += '/';
+            path += subdir;
+            DirectorySearch(path.c_str(), ext, &results);
+        }
+    }
+#endif
+
     return results;
 }