Add comment that goto_program_dereference doesn't specify language mode

Explicitly pass ID_nil instead of silently leaving the language uninitialised as before.

Author: smowton

src/pointer-analysis/goto_program_dereference.h

@@ -19,6 +19,10 @@ Author: Daniel Kroening, [email protected]
 class goto_program_dereferencet:protected dereference_callbackt
 {
 public:
+  // Note: this currently doesn't specify a source language
+  // for the final argument to value_set_dereferencet.
+  // This means that language-inappropriate values such as
+  // (struct A*)some_integer_value in Java, may be returned.
   goto_program_dereferencet(
     const namespacet &_ns,
     symbol_tablet &_new_symbol_table,
@@ -27,7 +31,7 @@ class goto_program_dereferencet:protected dereference_callbackt
     options(_options),
     ns(_ns),
     value_sets(_value_sets),
-    dereference(_ns, _new_symbol_table, _options, *this) { }
+    dereference(_ns, _new_symbol_table, _options, *this, ID_nil) { }
 
   void dereference_program(
     goto_programt &goto_program,

src/pointer-analysis/value_set_dereference.h

@@ -40,7 +40,7 @@ class value_set_dereferencet
     symbol_tablet &_new_symbol_table,
     const optionst &_options,
     dereference_callbackt &_dereference_callback,
-    const irep_idt _language_mode=irep_idt()):
+    const irep_idt _language_mode):
     ns(_ns),
     new_symbol_table(_new_symbol_table),
     options(_options),