Fix class loader issues in instrumentation tests.

The ASM ClassWriter uses a wimpy class loader when computing common
superclasses. This could cause a ClassNotFoundException in the
transform method (at reader.accept). This exception gets swallowed,
resulting in a class that should be instrumented to silently not
be. The fix is to override getCommonSuperClass to use the correct
class loader.

Trivia: This bug was discovered while 'stress-testing' this
instrumentation scheme on the Coursera students, to check that they
implement one method in terms of another in the assignment.

1 files changed, 28 insertions, 2 deletions

diff --git a/src/partest/scala/tools/partest/javaagent/ASMTransformer.java b/src/partest/scala/tools/partest/javaagent/ASMTransformer.java
index 09cd485d6b..a9a56d124d 100644
--- a/src/partest/scala/tools/partest/javaagent/ASMTransformer.java
+++ b/src/partest/scala/tools/partest/javaagent/ASMTransformer.java
@@ -26,9 +26,35 @@ public class ASMTransformer implements ClassFileTransformer {
         className.startsWith("instrumented/"));
   }
 	
-	public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) {
+	public byte[] transform(final ClassLoader classLoader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) {
 	  if (shouldTransform(className)) {
-  		ClassWriter writer = new ClassWriter(ClassWriter.COMPUTE_FRAMES | ClassWriter.COMPUTE_MAXS);
+  		ClassWriter writer = new ClassWriter(ClassWriter.COMPUTE_FRAMES | ClassWriter.COMPUTE_MAXS) {
+                        // this is copied verbatim from the superclass,
+                        // except that we use the outer class loader
+                        @Override protected String getCommonSuperClass(final String type1, final String type2) {
+                            Class<?> c, d;
+                            try {
+                                c = Class.forName(type1.replace('/', '.'), false, classLoader);
+                                d = Class.forName(type2.replace('/', '.'), false, classLoader);
+                            } catch (Exception e) {
+                                throw new RuntimeException(e.toString());
+                            }
+                            if (c.isAssignableFrom(d)) {
+                                return type1;
+                            }
+                            if (d.isAssignableFrom(c)) {
+                                return type2;
+                            }
+                            if (c.isInterface() || d.isInterface()) {
+                                return "java/lang/Object";
+                            } else {
+                                do {
+                                    c = c.getSuperclass();
+                                } while (!c.isAssignableFrom(d));
+                                return c.getName().replace('.', '/');
+                            }
+                        }
+                    };
   		ProfilerVisitor visitor = new ProfilerVisitor(writer);
   		ClassReader reader = new ClassReader(classfileBuffer);
   		reader.accept(visitor, 0);