Do not suppress instrumentation exceptions but rather propagate them …

…to mock maker that attempts instrumentation. Addresses #1005

src/main/java/org/mockito/internal/creation/bytebuddy/InlineBytecodeGenerator.java

@@ -31,7 +31,6 @@
 import java.lang.instrument.ClassFileTransformer;
 import java.lang.instrument.IllegalClassFormatException;
 import java.lang.instrument.Instrumentation;
-import java.lang.instrument.UnmodifiableClassException;
 import java.lang.reflect.Modifier;
 import java.security.ProtectionDomain;
 import java.util.Arrays;
@@ -41,6 +40,7 @@
 import static net.bytebuddy.implementation.MethodDelegation.withDefaultConfiguration;
 import static net.bytebuddy.implementation.bind.annotation.TargetMethodAnnotationDrivenBinder.ParameterBinder.ForFixedValue.OfConstant.of;
 import static net.bytebuddy.matcher.ElementMatchers.*;
+import static org.mockito.internal.util.StringUtil.join;
 
 public class InlineBytecodeGenerator implements BytecodeGenerator, ClassFileTransformer {
 
@@ -68,6 +68,8 @@ public class InlineBytecodeGenerator implements BytecodeGenerator, ClassFileTran
 
     private final BytecodeGenerator subclassEngine;
 
+    private volatile Throwable lastException;
+
     public InlineBytecodeGenerator(Instrumentation instrumentation, WeakConcurrentMap<Object, MockMethodInterceptor> mocks) {
         this.instrumentation = instrumentation;
         byteBuddy = new ByteBuddy()
@@ -113,11 +115,21 @@ private <T> void triggerRetransformation(MockFeatures<T> features) {
         if (!types.isEmpty()) {
             try {
                 instrumentation.retransformClasses(types.toArray(new Class<?>[types.size()]));
-            } catch (UnmodifiableClassException exception) {
+                Throwable throwable = lastException;
+                if (throwable != null) {
+                    throw new IllegalStateException(join("Byte Buddy could not instrument all classes within the mock's type hierarchy",
+                        "",
+                        "This problem should never occur for javac-compiled classes. This problem has been observed for classes that are:",
+                        " - Compiled by older versions of scalac",
+                        " - Classes that are part of the Android distribution"), throwable);
+                }
+            } catch (Exception exception) {
                 for (Class<?> failed : types) {
                     mocked.remove(failed);
                 }
                 throw new MockitoException("Could not modify all classes " + types, exception);
+            } finally {
+                lastException = null;
             }
         }
     }
@@ -169,6 +181,7 @@ public byte[] transform(ClassLoader loader,
                         .make()
                         .getBytes();
             } catch (Throwable throwable) {
+                lastException = throwable;
                 return null;
             }
         }