Add a badge for no_std-compatible crates

[Susurrus]

Right now there's a kind of hidden ecosystem of crates that support no_std (even more so for no_core). It'd be good if this was exposed more within crates.io. There's a category and you can sometimes search for it, but I'd like to suggest a badge be added for this. It will help people determine "crate quality" and also encourage library devs to provide no_std support for their crates (because everyone loves badges!).

[Susurrus]

This can be done by detecting if a crate exposes a std feature or not (precedent is here).

Also, I propose the color purple as it's not currently in use by any badges on the site and already exists in the color scheme.

[LunaBorowska]

I think detecting by no_std keyword is a better idea. I made a crate that is no_std usable, but doesn't have std feature, as there are no std-exclusive features - and I don't think I should have to add useless std feature just for a badge. For a different example, fixedvec.

[Susurrus]

@xfix You bring up a good point. Ideally this could detect both kinds of crates and display a badge for them.

[carols10cents]

Can you elaborate more on why the No Standard Library category doesn't meet this need?

[Susurrus]

The no_std category isn't a complete solution because:

• It segregates the ecosystem. It's not a feature category, it's a compatibility category. Even if I'm developing for no_std, I'm not browsing for compatibility I'm browsing for features. Making no_std cut across all categories (by adding a visible no_std badge to crates would be most helpful.
• It doesn't incentivize people to create or use crates that are no_std. The no_std community is quite small even though a lot more crates can support it than they do. By increasing visibility by putting up badges that even std users will see, it exposes them to that. Additionally making it a badge makes it something that can be "unlocked", which will entice some library creators to add it. It may also entice users to use a no_std-compatible crate over a std-only crate if they offer similar functionality improving the ecosystem for no_std users.

[markcatley]

This is a duplicate of #565.

[markcatley]

@sgrif

[Turbo87]

we've removed badges from crates.io a good while ago, so I guess we can close this issue too 😅