Enforce condition that generic references must refer to generic classes

We require that all generic references refer to generic classes

Also pulled out the conversion out of the loop and gave the variable a
more logical name

Added check for generic utils function

Author: thk123

src/java_bytecode/generate_java_generic_type.cpp

@@ -32,23 +32,25 @@ symbolt generate_java_generic_typet::operator()(
 
   INVARIANT(
     pointer_subtype.id()==ID_struct, "Only pointers to classes in java");
+  INVARIANT(
+    is_java_generic_class_type(pointer_subtype),
+    "Generic references type must be a generic class");
+
+  const java_generic_class_typet &generic_class_definition =
+    to_java_generic_class_type(to_java_class_type(pointer_subtype));
 
-  const java_class_typet &replacement_type=
-    to_java_class_type(pointer_subtype);
-  const irep_idt new_tag=build_generic_tag(
-    existing_generic_type, replacement_type);
-  struct_union_typet::componentst replacement_components=
-    replacement_type.components();
+  const irep_idt new_tag =
+    build_generic_tag(existing_generic_type, generic_class_definition);
+  struct_union_typet::componentst replacement_components =
+    generic_class_definition.components();
 
   // Small auxiliary function, to perform the inplace
   // modification of the generic fields.
   auto replace_type_for_generic_field =
     [&](struct_union_typet::componentt &component) {
 
       component.type() = substitute_type(
-        component.type(),
-        to_java_generic_class_type(replacement_type),
-        existing_generic_type);
+        component.type(), generic_class_definition, existing_generic_type);
 
       return component;
     };
@@ -61,8 +63,8 @@ symbolt generate_java_generic_typet::operator()(
     replacement_components.end(),
     replace_type_for_generic_field);
 
-  std::size_t after_modification_size=
-    replacement_type.components().size();
+  std::size_t after_modification_size =
+    generic_class_definition.components().size();
 
   INVARIANT(
     pre_modification_size==after_modification_size,

unit/testing-utils/generic_utils.cpp

@@ -8,6 +8,7 @@
 
 #include <util/ui_message.h>
 #include <java_bytecode/generate_java_generic_type.h>
+#include <util/namespace.h>
 #include "generic_utils.h"
 #include "catch.hpp"
 #include "require_type.h"
@@ -29,6 +30,10 @@ void generic_utils::specialise_generic(
       example_type.generic_type_variables().end(),
       is_java_generic_inst_parameter));
 
+  namespacet ns(new_symbol_table);
+  const typet &class_type = ns.follow(example_type.subtype());
+  REQUIRE(is_java_generic_class_type(class_type));
+
   // Generate the specialised version.
   ui_message_handlert message_handler;
   generate_java_generic_typet instantiate_generic_type(message_handler);