cosmwasm_std::entry_point parses data for disabled feature

[Buckram123]

cosmwasm_std::entry_point forward all arguments to the export function from the entry point function, even if this argument should not be included in this feature.
I think it's best to see as minimal example

pub struct InstantiateMsg<N> {
    pub number: N,
}

#[cosmwasm_std::entry_point]
pub fn instantiate(
    deps: DepsMut,
    env: Env,
    info: MessageInfo,
    #[cfg(feature = "u32")] msg: InstantiateMsg<u32>,
    #[cfg(not(feature = "u32"))] msg: InstantiateMsg<u64>,
) -> Result<Response, Never> {
    Ok(Response::new())
}

Compiling it with "u32" or without "u32" feature enabled will error with:

error[E0061]: this function takes 4 arguments but 5 arguments were supplied
   --> contracts/cw-blob/src/lib.rs:8:1
    |
8   | #[cosmwasm_std::entry_point]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unexpected argument of type `u32`
    |
note: function defined here
   --> /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/cosmwasm-std-2.1.3/src/exports.rs:115:8
    |
115 | pub fn do_instantiate<Q, M, C, E>(
    |        ^^^^^^^^^^^^^^
    = note: this error originates in the attribute macro `cosmwasm_std::entry_point` (in Nightly builds, run with -Z macro-backtrace for more info)

[Buckram123]

Working workaround is making wrapper around instantiate function and having both instantiate functions included

Based on the example from the issue description:

#[cfg(feature = "u32")]
#[cosmwasm_std::entry_point]
pub fn instantiate(
    deps: DepsMut,
    env: Env,
    info: MessageInfo,
    msg: InstantiateMsg<u32>,
) -> Result<Response, Never> {
    _instantiate(deps, env, info, msg)
}

#[cfg(not(feature = "u32"))]
#[cosmwasm_std::entry_point]
pub fn instantiate(
    deps: DepsMut,
    env: Env,
    info: MessageInfo,
    msg: InstantiateMsg<u64>,
) -> Result<Response, Never> {
    _instantiate(deps, env, info, msg)
}

pub fn _instantiate(
    _deps: DepsMut,
    _env: Env,
    _info: MessageInfo,
    #[cfg(feature = "u32")] _msg: InstantiateMsg<u32>,
    #[cfg(not(feature = "u32"))] _msg: InstantiateMsg<u64>,
) -> Result<Response, Never> {
    Ok(Response::new())
}

[chipshort]

You have a point here. This is a result of the way the entry_point macro is implemented.
The problem is that we go through all the parameters of the entrypoint function and create a pointer for each one that is passed to the actual entrypoint function. The problem is that the conditional compilation happens after the macro runs and the macro ignores all attributes. With your example, it basically generates code like this:

mod __wasm_export_instantiate {
    #[no_mangle]
    extern "C" fn instantiate(env_ptr: u32, info_ptr: u32, msg_ptr: u32, msg_ptr2: u32) -> u32 {
        cosmwasm_std::do_instantiate(&super::instantiate, env_ptr, info_ptr, msg_ptr, msg_ptr2)
    }
}

In this specific case, the only fix I can think of would be to keep the cfg attribute on the ptr parameter and argument, but I don't know if that's fine for all attributes.

[Buckram123]

You have a point here. This is a result of the way the entry_point macro is implemented. The problem is that we go through all the parameters of the entrypoint function and create a pointer for each one that is passed to the actual entrypoint function. The problem is that the conditional compilation happens after the macro runs and the macro ignores all attributes. With your example, it basically generates code like this:

mod __wasm_export_instantiate {
    #[no_mangle]
    extern "C" fn instantiate(env_ptr: u32, info_ptr: u32, msg_ptr: u32, msg_ptr2: u32) -> u32 {
        cosmwasm_std::do_instantiate(&super::instantiate, env_ptr, info_ptr, msg_ptr, msg_ptr2)
    }
}

In this specific case, the only fix I can think of would be to keep the cfg attribute on the ptr parameter and argument, but I don't know if that's fine for all attributes.

Won't it be better then to just ignore how many arguments entry point have and just generate always the same extern function? So instead of counting arguments, instantiate will have always 3 pointers

[chipshort]

That already doesn't work as a full solution because we just introduced an additional version of migrate with 3 arguments (instead of the 2 it had until now).