PluginInfo: fall back to @plugin class annotation

Normally, plugins are discovered by scanning the SJC annotation index,
present in the resource META-INF/json/org.scijava.plugin.Plugin.

However, PluginInfo objects can also be created explicitly and added
directly to a PluginIndex. This is especially useful for unit tests.
When this happens, the PluginInfo(String, Class) constructor passed a
null Plugin annotation, resulting in no plugin metadata at all. It is
much better for the code path through that constructor to scrap the
given Class for its associated Plugin annotation, if any.

Author: ctrueden

src/main/java/org/scijava/plugin/PluginInfo.java

@@ -177,10 +177,14 @@ protected PluginInfo(final String className,
 		setPluginType(pluginType);
 		setMenuPath(null);
 		setMenuRoot(UIDetails.APPLICATION_MENU_ROOT);
-		if (annotation != null) {
-			this.annotation = annotation;
-			populateValues();
+		if (annotation == null) {
+			// attempt to obtain the annotation from the plugin class, if available
+			if (pluginClass != null) {
+				this.annotation = pluginClass.getAnnotation(Plugin.class);
+			}
 		}
+		else this.annotation = annotation;
+		populateValues();
 		this.classLoader = classLoader;
 	}