[bug#35318] [PATCH] Update cargo-build-system to expand package inputs

[Ivan Petkov <ivanppetkov@gmail.com>]

Hi Ludo!

> On May 20, 2019, at 12:38 PM, Ludovic Courtès <ludo@gnu.org> wrote:
> 
>> +(define (package-cargo-deps p)
>> +  (apply
>> +    (lambda* (#:key (cargo-deps '()) #:allow-other-keys)
>> +      cargo-deps)
>> +    (package-arguments p)))
> 
> It’s surprising style.  It seems redundant with the ‘inputs’ field, but
> IIUC, the main difference here is that you can simply name dependencies,
> even if there’s no Guix package for it, right?

That’s one benefit, the other is that we’re defining our own new semantics
on the cargo-specific inputs here to be treated like propagated-inputs, but
without actually making the store install them when a Rust binary is substituted.

>> +(define (package-cargo-dev-deps p)
>> +  (apply
>> +    (lambda* (#:key (cargo-dev-deps '()) #:allow-other-keys)
>> +      cargo-dev-deps)
>> +    (package-arguments p)))
> 
> As a rule of thumb, please avoid abbreviations in identifiers (info
> "(guix) Coding Style").  So that would be
> ‘package-development-dependencies’ or something like that.

Thanks for the tip, I’ll update these names. 

Since the actual cargo documentation actually refers to “dev-dependencies”
do you think it’s better to use “cargo-dev-dependencies” (for consistency that
Rust programmers might be used to), or stick with “cargo-development-dependencies”
(for Guix consistencies)?

>> +(define (crate-transitive-deps inputs)
>> +  "Return the closure of INPUTS when considering the 'cargo-deps' and
>> +'cargod-dev-deps' edges.  Omit duplicate inputs, except for those
>> +already present in INPUTS itself.
>> +
>> +This is implemented as a breadth-first traversal such that INPUTS is
>> +preserved, and only duplicate extracted inputs are removed.
>> +
>> +Forked from ((guix packages) transitive-inputs) since this extraction
>> +uses slightly different rules compared to the rest of Guix (i.e. we
>> +do not extract the conventional inputs)."
> 
> Perhaps call it ‘crate-closure’?

Sure that works, I’ll rename this!

>> +(define (expand-crate-sources cargo-deps cargo-dev-deps)
>> +  "Extract all transitive sources for CARGO-DEPS and CARGO-DEV-DEPS along their
>> +'cargo-deps' edges.
> 
> Maybe s/cargo-deps/inputs/ and s/cargo-dev-deps/development-inputs/?
> 
> I’d prefer to stick to the same terminology as in the rest of the code
> if we’re talking about the same sort of input lists.

I can rename this as well.

> 
> That’s it.  :-)
> 
> Thank you for improving Rust support!

Happy to help :)

—Ivan