Fold/Unfold Error

[colinlgray]

Hi all, I'm trying to run prusti on some existing code and running into a fold/unfold error. I'm just learning rust so I'm not knowledgable enough to know what exactly is causing it

Error:

error: [Prusti internal error] Prusti encountered an unexpected internal error
  --> memo/program/src/lib.rs:30:1
   |
30 | / pub fn build_memo(memo: &[u8], signer_pubkeys: &[&Pubkey]) -> Instruction {
31 | |     Instruction {
32 | |         program_id: id(),
33 | |         accounts: signer_pubkeys
...  |
38 | |     }
39 | | }
   | |_^
   |
   = note: We would appreciate a bug report: https://github.com/viperproject/prusti-dev/issues/new
   = note: Details: cannot generate fold-unfold Viper statements. The required permission Acc(_8.closure_0.val_ref, read) cannot be obtained.

The full code for this can be found here: https://github.com/solana-labs/solana-program-library/blob/master/memo/program/src/lib.rs#L30

[fpoli]

It's because Prusti does not support well signatures with types that contain references. The signer_pubkeys: &[&Pubkey] parameter is a case of that: an array type that contain references to Pubkey.

The error message should be more readable, e.g. "feature xyz is not supported", but it seems that we miss a check on the types used in the signature.