External messages - accept_message seems to cause silent failures about sandbox HOT 5 CLOSED

It is funC related behavior, not TVM/sandbox.
The thing is that load_ref is considered pure (while actually it can be impure if throw exception). In other words funC drops load_ref operation if result is not used:
Both

;; This will throw an error, as expected (assuming the slice doesn't in fact contain a ref)
() recv_external(slice in_msg) impure {
  var x = in_msg~load_ref();
  accept_message();
}

and

;; This will NOT throw an error
() recv_external(slice in_msg) impure {
  accept_message();
  var x = in_msg~load_ref();
}

will compile to

recv_external PROC:<{
  DROP
  ACCEPT
}>

from sandbox.

This explains why the error isn't thrown when the loaded ref isn't used.

But in this case:

() recv_external(slice in_msg) impure {
  accept_message();
  var x = in_msg~load_ref();
  ~dump x;
}

The value is used. Shouldn't an error be thrown then?

from sandbox.

() recv_external(slice in_msg) impure {
  accept_message();
  var x = in_msg~load_ref();
  ~dump x;
}

compiles to

recv_external PROC:<{
  ACCEPT
  LDREF
  DROP
  s0 DUMP
  DROP
}>

so yes, I'm expecting failed transaction in this case

from sandbox.

This explains why the error isn't thrown when the loaded ref isn't used.

But in this case:

() recv_external(slice in_msg) impure {
  accept_message();
  var x = in_msg~load_ref();
  ~dump x;
}

The value is used. Shouldn't an error be thrown then?

With this code, I'm getting exit code 9 (to be expected). Do you get the same result?

from sandbox.

I'll check, it was probably a misunderstanding of mine of how errors work before and after accepting messages. will reopen issue if needed

from sandbox.