build fails when selecting serde feature but not std feature

[Trevor Spiteri]

Build fails with this dependency setting:

[dependencies.half]
version = "2"
default-features = false
features = ["serde"]

Adding the "std" feature makes the build work.

[dependencies.half]
version = "2"
default-features = false
features = ["serde", "std"]

[Trevor Spiteri]

There are two possible solutions I can think of:

1. Make the serde feature depend on the std feature. With rust 1.60 this would be simple; just add a new feature in Cargo.toml:

   [features]
   serde = ["dep:serde", "std"]

   But with earlier rust I didn't manage to get it to work. I tried to import serde with a different name e.g.

   [dependencies]
   serde_crate = { package = "serde", version = "1.0" ... }

   and then use serde_crate instead of serde in the code, or add

   #[cfg(feature = "serde")]
   extern crate serde_crate as serde;

   but that broke derive(Serialize). Maybe a manual implementation could replace the derive, or there's another fix, but I am completely unfamiliar with serde's derives.

2. Otherwise features that are now gated with #[cfg(feature = "serde")] could be gated with #[cfg(all(feature = "serde", feature = "std"))] instead.

(Some serde stuff just depends on alloc not on std.)

[Shane F. Carr]

Just hit this issue. Would appreciate a dot release on the 2.x channel to fix it.