rust: cargo build-system: how to handle libraries

[ng0]

Hi,

I've got about 94 rust packages on my todo list for our
(secushare) current prototype version.

Today I assembled the full list of them and started with the
crate `libc`. This crate comes with no Cargo.toml file, where I
already am aware of the limitation of our cargo build-system.

Before I can start my task now, I have to enhance the cargo
build-system in guix. Now I'm very new to packaging for
rust. When a Cargo.toml is in place, you can find lots of
information very easily in search engines, but without it gets
very difficult.

Please correct me if this is wrong:

We run (or this is the default) cargo with `--bin`, which is
necessary for everything which needs to be compiled and features
a Cargo.toml.

To "build" libraries, we have to explicitly tell cargo to not
run/build/whatever with --bin ?
Or do I have to interprete what I read a while ago "we just need
to copy the libraries to the store" as literally "if we encounter
no Cargo.toml, let's copy everything to the store as is"?

CC'ing David, Eric, and Ludovic as you all were involved to some
degree in the discussion before about cargo and rust.
-- 
♥Ⓐ  ng0
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