Hi Chris,
Sorry for taking so long to review this. In short, I think these
changes are good, and if nobody has more feedback in the next few days,
I will merge it and we can see how it works in practice!
Thanks for the feedback, and thanks for the wonderful pros and cons summary! Cons:
- Because the "dependencies" and "dev-dependencies" are specified as
package arguments instead of any kind of "input", they won't show
up in some of the graphs produced by "guix package". However, in
theory "guix graph" could be taught to display nodes for crate
"dependencies" and "dev-dependencies", too.
Totally correct, we can iterate on this in the future. - Everyone who defines a Guix package for a crate must make sure the
origin's file name ends in ".cargo", since the cargo-build-system
now assumes that any input ending in ".cargo" is a crate that
should be extracted into the build's crate-dir. This is a little
brittle, and I wish we had a better way to check this, but I can't
think of a better way at the moment. Since you've updated the
importer to always add this, it probably won't be much of an issue
in practice, since that's the default way new crates will be added
to Guix. Going forward, maybe we can avoid this by just checking
the inputs to see which ones are gzipped tarballs containing
Cargo.toml files.
We discussed an alternative solution to this offline, namely we can ask tar to check if a Cargo.toml file exists at the top level without fully unpacking the archive. If it exists, we can assume the tarball is a crate source and only then unpack it in the vendor directory.
This will make things less brittle as the `.crate` convention won’t be necessary (a potential downside would be that if there happens to be some arbitrary input which happens to be a tarball which happens to have a Cargo.toml, it will get included in the vendor directory without us knowing about it. I think the chances of this happening in practice are virtually zero, so we can iterate on this if it ever becomes a problem).
I’m going to try to update the patch series to include this change over the next few days (along with Ludo’s naming-related feedback). If I don’t get a chance to finish this, we can always merge it in later! Limitations imposed by Rust/Cargo itself:
- I'm not a Rust or Cargo expert, but my current understanding is
that it isn't feasible to save the artifacts produced when
building a crate for re-use when building another crate. In the
world of C, it is common to produce a library, and then link
against that library when building other software later. In Guix,
when building a C library, we install the built artifacts (e.g.,
.so files) into the output, so that those artifacts can be used as
the input for another package's build. It seems that, by Cargo's
design, it isn't currently feasible to do the same sort of thing
with Cargo: that is, it isn't feasible to build artifacts, install
them somewhere for later use, and then later re-use them in
another Cargo build. I'd be glad to learn that I'm mistaken, but
currently that is my understanding.
Your understanding here is correct. - Related to this, I doubt that a Rust programmer will be able to
invoke a command like "guix environment my-crate" (even if we
teach it to understand crate "dependencies" and
"dev-dependencies") to make all the dependencies required to build
my-crate available. If a Rust programmer wants to hack on
my-crate, they'll probably still just use "cargo" to do it without
using Guix at all. Is there any way to avoid this and make it
possible to get the dependencies used by Guix in the build, so
that a Rust programmer can hack around using precisely those
dependencies? If this were C or Python, you could do that using
"guix environment," but I'm not sure how this could work with Rust
crates.
Correct again, a programmer will not be able to run `guix environment my-crate`, however, I don’t think anyone will do this in practice, since you can’t “point” cargo at that source closure/outputs anyway.
For hacking on Rust crates, I’d imagine a Rust programmer would simply stick with cargo and the crates.io ecosystem proper. I don’t ever see guix as being a replacement for crates.io (it would be impossible to keep up with the package changes, even if we automate things, crates aren’t guaranteed to even build, etc.).
I’d imagine that crates should only be imported into guix if they’re necessary for supporting an actual application or service written in Rust, but not used for day-to-day development.
—Ivan
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