Use vec![] for instantiate an empty vector in nonempty! macro

[greyblake]

It fixes #68

I hope using vec![] should not be a big problem, cause vec![] is already used in another branch of the macro.

Thank you again for you work!

[FintanH]

Thanks for the contribution! @nuttycom would vec! work here, or would that mean that std is required? It seems like the no-std builds successfully, so perhaps it's fine!

[greyblake]

@FintanH

vec![] is already used in another branch of the macro, so I would assume it does not make it worse :D

[nuttycom]

Hmmm, I am not sure here. I think the existing use of `vec` may actually be a bug, I just didn’t notice it because there there are no uses of the `nonempty` macro in a context where no-std is enforced and not automatically enabled. `vec!` itself is part of `std`: https://doc.rust-lang.org/std/macro.vec.html So it could be that you can’t use the macro in a no-std context, but because it’s a macro if it’s never used there is no problem. What is probably needed to demonstrate the issue is a CI task like the one I added here: zcash/orchard#450 but with the generated lib.rs file containing some code that invokes the `nonempty` macro. I'm not sure what the best way to make sure that `extern crate alloc` is added to the generated code is, though.

…

On Mon, Jan 6, 2025 at 8:18 PM Serhii Potapov ***@***.***> wrote: @FintanH <https://github.com/FintanH> vec![] is already used in another branch of the macro, so I would assume it does not make it worse :D image.png (view on web) <https://github.com/user-attachments/assets/1acb9b23-78dd-4daf-8b89-b61ccadac33d> — Reply to this email directly, view it on GitHub <#69 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAGXR3Q6OZKCU7KUAWHZC32JLCHVAVCNFSM6AAAAABUB3IE6GVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDKNZTGY2TSMJYGE> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[d-k-bo]

vec! itself is part of std

It is actually part of alloc: https://doc.rust-lang.org/alloc/macro.vec.html

It looks like it requires a #[macro_use] on alloc to compile, take a look at this example:

#![no_std]

#[macro_use]
extern crate alloc;

fn main() {
    vec![0];
}

[FintanH]

Ok, so afaiu this change is fine because the no-std actions check uses --no-default-features which means that std is not enabled, and all other dependencies are optional – so also not enabled – and it passes just fine :) I'll merge and push a hotfix version

[greyblake]

@FintanH Thanks!