What is the scope of no_std support?

[yanshay]

I'm trying to use Snafu in a no_std environment, and the basic example from the docs doesn't work.

It can't find Whatever and I checked the sourced and it's behind std feature.

So what is the scope of support for no_std?

[alerque]

As far as I understand it whatever itself does not support no_std, so this doesn't seem unexpected.

[yanshay]

As far as I understand it whatever itself does not support no_std, so this doesn't seem unexpected.

Oh, any technical reason for that?
If I understand correctly whatever is the equivalent to anyhow crate and I recall I used it in the past in no_std.

[shepmaster]

Yes, snafu::Whatever requires the standard library for allocation (via Box and String) as well as the Backtrace type which should usually be provided by the standard library on modern Rust versions.

From anyhow's README (emphasis mine):

To depend on Anyhow in no_std mode, disable our default enabled “std” feature in Cargo.toml. A global allocator is required.

So anyhow works with libcore + liballoc. I'd expect that SNAFU could do the same ¹ and just no one has needed that specific distinction yet. Do you have liballoc available?

Footnotes

1. Or close to the same; you could always define your own Whatever at least. ↩

[yanshay]

So anyhow works with libcore + liballoc. I'd expect that SNAFU could do the same 1 and just no one has needed that specific distinction yet. Do you have liballoc available?

I have alloc. In embedded there is a distinction between std and alloc since alloc is quite common to have.

[shepmaster]

there is a distinction between std and alloc

I'm aware 😄. It's just that most of my embedded usage / knowledge of usage has been places with no allocation capability (e.g. tiny devices, Windows kernel drivers). In addition, I don't like using Whatever because I don't want to allocate if I can ever help it, plus I like having a known set of errors.

Anyway, can you try this branch and see if it works for your case?

https://github.com/shepmaster/snafu/tree/alloc

That should look something like this in your Cargo.toml:

[dependencies.snafu]
default-features = false
features = ["rust_1_81", "alloc"]
git = "https://github.com/shepmaster/snafu"
branch = "alloc"