[Bug] debug::print fails module verification

[jamescarter-le]

Steps to Reproduce Issue

When using debug::print in a module, it will fail move prove checks.

Please see very simple example repo: https://github.com/jamescarter-le/sui_bytecode_fail

Expected Result

debug::print should not fail move prove checks, or the compiler should raise this as an error.

Actual Result

sui client publish returns:
Move Bytecode Verification Error. Please run the Bytecode Verifier for more information. from sui start
RPC call failed: ErrorObject { code: ServerError(-32000), message: "Move Bytecode Verification Error. Please run the Bytecode Verifier for more information.", data: None } from the current devnet.

PS SuiDev\my_move_package> sui move test
INCLUDING DEPENDENCY MoveStdlib
INCLUDING DEPENDENCY Sui
BUILDING MyGame         
Running Move unit tests
....
Test result: OK. Total tests: 21; passed: 21; failed: 0
PS SuiDev\my_move_package> sui move build                      
PS SuiDev\my_move_package> sui client publish --gas-budget 3000
Move Bytecode Verification Error. Please run the Bytecode Verifier for more information.

System Information

• OS: Windows 10
• Compiler: sui 0.6.2

[awelc]

I have looked into it and the first thing to note (I also mentioned this on Discord) is that this is NOT a Move prover problem but rather an issue related to module verification (and, apparently, not even that as described below).

The real issue here is that it's not the verifier that fails but rather the linker as we do not include the debug module in the set of Move stdlib modules we utilize in Sui (at least outside of test mode):

sui/crates/sui-framework-build/src/lib.rs

Line 20 in ec42308

#[cfg(not(test))]

If I understand it correctly, the debug module is simply not included in the devnet's genesis image.

Of course one of the problems here is that the error message that is passed to the user is quite opaque. Furthermore, running the verifier will (at this point) not help here as this is the linker problem. It's unfortunately not easy to pass the detailed error message to the user as the same messages are store on-chain and have to be succinct, generic, and stable in the face of future changes (@tnowacki should be able to provide more context here if need be). Still, there are some solutions that can help mitigate this problem, in particular (as discussed with @tnowacki):

• we made the debug module [#test_only] (either upstream or just in Sui) to prevent using debug::print in "regular" code altogether
• we modify Sui module building procedure (used by both sui move build and sui client publish) to report an error in the specific case of the code from the debug module being included in the code being built/published
• we add the debug module to devnet's genesis image (the native method implementing debug::print is a no-op outside of test mode anyways - we could still charge some outrageous amount of gas for "executing" it on-chain to discourage people leaving debug statements in their code)

It would be great to get some feedback on this (@sblackshear, @lxfind, @oxade? - please add others to the discussion if need be).

[tnowacki]

+1 for making the module test_only, even on the main move-lang repo.

The native function has this check of #[cfg(feature = "testing")] to make it a no-op in a live repo. This was really a hack before the unit testing framework was around IMO. I think it makes everything feel a bit more consistent to just slap on a test_only annotation

[awelc]

Resolved in #4356