Add a little pointer-cast helper to dbg.

Author: froystig

src/lib/dbg.rs

@@ -14,6 +14,7 @@ native "rust" mod rustrt {
   fn debug_tag[T](&T x);
   fn debug_obj[T](&T x, uint nmethods, uint nbytes);
   fn debug_fn[T](&T x);
+  fn debug_ptrcast[T, U](@T x) -> @U;
 }
 
 fn debug_vec[T](vec[T] v) {
@@ -52,3 +53,7 @@ fn debug_obj[T](&T x, uint nmethods, uint nbytes) {
 fn debug_fn[T](&T x) {
   rustrt.debug_fn[T](x);
 }
+
+fn ptr_cast[T, U](@T x) -> @U {
+  ret rustrt.debug_ptrcast[T, U](x);
+}

src/rt/rust_builtin.cpp

@@ -340,6 +340,19 @@ debug_fn(rust_task *task, type_desc *t, rust_fn *fn)
     task->log(rust_log::STDLIB, "  closure at 0x%" PRIxPTR, fn->closure);
 }
 
+extern "C" CDECL void *
+debug_ptrcast(rust_task *task,
+              type_desc *from_ty,
+              type_desc *to_ty,
+              void *ptr)
+{
+    task->log(rust_log::STDLIB, "debug_ptrcast from");
+    debug_tydesc_helper(task, from_ty);
+    task->log(rust_log::STDLIB, "to");
+    debug_tydesc_helper(task, to_ty);
+    return ptr;
+}
+
 
 //
 // Local Variables: