GIANT FAT WARNINGS if you use any code in net.minecraft.src or any subpackage thereof. Get it out of there, now!

common/cpw/mods/fml/common/ModContainerFactory.java

@@ -25,6 +25,14 @@ public class ModContainerFactory
             return new ModLoaderModContainer(className, modSource, modParser.getBaseModProperties());
         }
 
+        // We warn if it's not a basemod instance -- compatibility requires it to be in net.minecraft.src *sigh*
+        if (className.startsWith("net.minecraft.src."))
+        {
+            FMLLog.severe("FML has detected a mod that is using a package name based on 'net.minecraft.src' : %s. This is generally a severe programming error. "
+                    + " There should be no mod code in the minecraft namespace. MOVE YOUR MOD! If you're in eclipse, select your source code and 'refactor' it into "
+                    + "a new package. Go on. DO IT NOW!",className);
+        }
+
         for (ModAnnotation ann : modParser.getAnnotations())
         {
             if (ann.getASMType().equals(Type.getType(Mod.class)))