Hi Ivan,
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!
At a high level, I think these changes have the following pros and cons:
Pros:
- We can now build Rust crates. Fantastic!
- The "dependencies" and "dev-dependencies" terminology is the same
as Cargo uses, so it will be familiar to Rust programmers.
- We avoid O(N^2) build time, where N is the number of dependencies.
- We can use the importer to quickly import new crates and iterate.
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.
- 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.
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.
- 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.
Thanks again for working on this!
--
Chris
