Add ability to overlay classes with new definitions of existing methods

Allows multiple definitions of the same class to appear on the classpath, so long as all but the first definition are marked with the attribute @java::com.diffblue.security.OverlayClassImplementation. Overlay class definitions can contain methods with the same signature as methods in the original class, so long as these are marked with the attribute @java::com.diffblue.security.OverlayMethodImplementation; such overlay methods are replaced in the original file with the version found in the last overlay on the classpath. Later definitions can also contain new supporting methods and fields that are merged in.
This will allow insertion of Java methods into library classes to handle, for example, modelling dependency injection.

Author: NathanJPhillips

regression/cbmc-java/generics_type_param/test.desc

@@ -3,9 +3,9 @@ GenericFields$SimpleGenericField.class
 --cover location --function GenericFields\$SimpleGenericField.foo --verbosity 10
 ^EXIT=0$
 ^SIGNAL=0$
-Reading class AWrapper
-Reading class FWrapper
-Reading class IWrapper
+Parsing class AWrapper
+Parsing class FWrapper
+Parsing class IWrapper
 --
 failed to load class \`AWrapper\'
 failed to load class \`FWrapper\'

src/java_bytecode/ci_lazy_methods.cpp

@@ -85,15 +85,15 @@ bool ci_lazy_methodst::operator()(
       reachable_classes.push_back(main_class);
     else
       reachable_classes = main_jar_classes;
-    for(const auto &classname : reachable_classes)
+    for(const irep_idt &class_name : reachable_classes)
     {
-      const auto &methods=
-        java_class_loader.class_map.at(classname).parsed_class.methods;
+      const auto &methods =
+        java_class_loader.get_original_class(class_name).parsed_class.methods;
       for(const auto &method : methods)
       {
-        const irep_idt methodid="java::"+id2string(classname)+"."+
-          id2string(method.name)+":"+
-          id2string(method.descriptor);
+        const irep_idt methodid =
+          "java::" + id2string(class_name) + "." + id2string(method.name)
+            + ":" + id2string(method.descriptor);
         method_worklist2.push_back(methodid);
       }
     }