Update method source location info

The line number is not the line number of the first instruction because
that can be unassigned. Instead, set it to the line number of the first
instruction that does have a line number assigned.

Set location function to be the name of the method itself.

Author: svorenova

jbmc/src/java_bytecode/java_bytecode_parser.cpp

@@ -1256,10 +1256,23 @@ void java_bytecode_parsert::rmethod_attribute(methodt &method)
           id2string(method.name)+":"+method.descriptor);
     }
 
-    // line number of method
+    // line number of method (the first line number available)
     if(!method.instructions.empty())
-      method.source_location.set_line(
-        method.instructions.begin()->source_location.get_line());
+    {
+      const auto it = std::find_if(
+        method.instructions.begin(),
+        method.instructions.end(),
+        [&](const instructiont &instruction) {
+          return !instruction.source_location.get_line().empty();
+        });
+      if(it != method.instructions.end())
+        method.source_location.set_line(it->source_location.get_line());
+    }
+
+    // method name
+    method.source_location.set_function(
+      "java::" + id2string(parse_tree.parsed_class.name) + "." +
+      id2string(method.name) + ":" + method.descriptor);
   }
   else if(attribute_name=="Signature")
   {