No_std = true metadata in Cargo.toml

I think it would be useful to support a no_std = true flag in Cargo.toml, or a similar flag that indicates a crate has a #![no_std] compatible mode.

I don’t think this flag needs to have any affect on the build process, or to replace e.g. having an optional std feature enabled by-default (perhaps it could, but consider that a non-goal for now).

Instead, I think a no_std = true flag would be useful for the following reasons:

  • Visually displaying a “no_std compatible” indication on a crate’s page on
  • Enabling search to filter by packages that support no_std
  • cargo could warn if any of your dependencies do not have this flag (clearly there’d be a lot of false positives at first, but eventually it could be quite useful)

Has this been suggested before?

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I think might cover something like this?

Nice! That looks promising

I’ve proposed a bit more general concept here. Hope something similar will be included into this RFC.

In the meantime, we can encourage the keyword no_std for such crates.

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Support for categorizing crates in was added shortly after I asked this question. I figured it might be worth adding a category to allow easy browsing of #![no_std] crates:


First is either :wink: thanks to @mglagla

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