Added support for adding arbitrary classpath entries.

core/src/main/java/com/threerings/getdown/data/Application.java

@@ -345,6 +345,15 @@ public class Application
         return _resources;
     }
 
+    /**
+     * Returns a list of strings (usually file paths relative to the app root dir) to add to the
+     * classpath.
+     */
+    public List<String> getClassPathDirectories ()
+    {
+        return _cpdirs;
+    }
+
     /**
      * Returns the digest of the given {@code resource}.
      */
@@ -751,6 +760,7 @@ public class Application
         _jvmargs.clear();
         _appargs.clear();
         _txtJvmArgs.clear();
+        _cpdirs.clear();
 
         String appPrefix = _envc.appId == null ? "" : (_envc.appId + ".");
 
@@ -781,6 +791,9 @@ public class Application
         // look for custom arguments
         fillAssignmentListFromPairs("extra.txt", _txtJvmArgs);
 
+        // add any extra classpath entries
+        addAll(config.getMultiValue(appPrefix + "classpath"), _cpdirs);
+
         // extract some info used to configure our child process on macOS
         _dockName = config.getString("ui.name");
         _dockIconPath = config.getString("ui.mac_dock_icon", "../desktop.icns");
@@ -1758,6 +1771,7 @@ public class Application
 
     protected List<Resource> _codes = new ArrayList<>();
     protected List<Resource> _resources = new ArrayList<>();
+    protected List<String> _cpdirs = new ArrayList<>();
 
     protected int _verifyTimeout = 60;
 

core/src/main/java/com/threerings/getdown/data/PathBuilder.java

@@ -9,6 +9,7 @@ import java.io.File;
 import java.io.IOException;
 import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import java.util.zip.ZipFile;
 
@@ -43,6 +44,7 @@ public class PathBuilder
         for (Resource resource : app.getActiveCodeResources()) {
             classPathEntries.add(resource.getFinalTarget());
         }
+        addClassPathDirectories(app, classPathEntries);
         return new ClassPath(classPathEntries);
     }
 
@@ -70,9 +72,21 @@ public class PathBuilder
             classPathEntries.add(entry);
         }
 
+        addClassPathDirectories(app, classPathEntries);
+
         return new ClassPath(classPathEntries);
     }
 
+    private static void addClassPathDirectories (Application app, Set<File> classPathEntries) {
+        for (String cpdir : app.getClassPathDirectories()) {
+            File cpfile = new File(cpdir);
+            if (!cpfile.isAbsolute()) {
+                cpfile = new File(app.getAppDir(), cpdir);
+            }
+            classPathEntries.add(cpfile);
+        }
+    }
+
     /**
      * Builds a {@link ClassPath} instance by first caching all native jars (indicated by
      * nresource=[native jar]), unpacking them, and referencing the locations of each of the