External messages - accept_message seems to cause silent failures

[shaharyakir]

Describe the bug
External messages - accept_message seems to cause silent failures

To Reproduce

;; 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();
  ~dump x; ;; Without this line, error doesn't get thrown
}

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

Expected behavior
I'd expect:

1. Error to be thrown upon loading of the ref (9: cell underflow), regardless of whether we're using the value (using ~dump, send_raw_message, etc.)
2. Error to be thrown regardless of message having been accepted.

Actual behavior
Error is thrown only if the loading which causes the underflow happens before accepting the message.

System information

• Package version: 0.4.0
• Node version: v16.15.0
• OS name and version: Mac OS M1 Ventura 13.0

Additional context
Add any other context about the problem here.

[EmelyanenkoK]

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
}>

[shaharyakir]

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?

[EmelyanenkoK]

() 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

[krigga]

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?

[shaharyakir]

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