Hartmut Goebel schreef op do 31-03-2022 om 21:47 [+0200]:
since rust does not support anything like static or dynamic libraries, 
building (intermediate) crates is useless like a hole in my head. Any 
output on any intermediate crate will just be thrown away.

In my experiments, it looks like the rust compiler actually _does_
support static libraries, though perhaps cargo doesn't.

I invite you to take a look at <https://notabug.org/maximed/cargoless-rust-experiments>.
It contains a minimal rust library (libhello) and a minimal 'hello
world'-style application that uses 'libhello'.

To simulate how Guix compiles C software (but here applied to Rust), 
the Makefile does the following:

  * Run 'rustc --crate-type=lib libhello/hello.rs -o out/libhello/lib/libhello.rlib',
    to compile the library and install it in 'out/libhello/lib/libhello.rlib'
    (cf. /gnu/store/...-libhello.../lib/hello.so).

  * Run 'rustc -Lout/libhello/lib hello-app/main.rs -o out/hello-oxygen/bin/hello'
    to compile the application.  By default, rustc will fail because it cannot find
    the library.  However, if -Lout/libhello/lib is passed, then it does find it!

    (cf. LIBRARY_PATH=/gnu/store/.../lib & gcc -L/gnu/store/.../lib)

This is a rather basic example (no transitive dependencies, no test dependencies,
no macros ...), but it seems like there are some possibilities here ...

As a next step, maybe I could try writing a Guix package definition for libhello
and hello-oxygen, gradually making things more complicated (macros, transitive
dependencies, some non-toy Rust dependencies, a Guix build system ...)?

Greetings,
Maxime.