Some updates:

  * core-updates is now targeted instead of master (because the librsvg
    on core-updates has a less complicated build system and hence easier
    to support with antioxidant)
  * librsvg now builds. It's about 3 times larger than the
    cargo-build-system librsvg (at least, the librsvg from master,
    didn't compare against core-updates yet because there was no
    substitute available), so perhaps some compilation flags need to be
    changed.
  * According to ci.guix.gnu.org, antioxidation is at 90%, but some of
    the 'failures' are because of cancelled builds in dependencies, the
    real number should be higher. Maybe 'Restart all builds' would be
    correct that, though I don't know if that wouldn't restart too much
    builds (including builds that succeeded).
  * Running tests is supported, #:tests? and #:parallel-tests? is
    respected, there is an option to skip some tests (using
    #:test-options).  As antioxidant doesn't do #:skip-build? #t, I
    expect more packages to be tested with antioxidant than with
    cargo-build-system.

    There are some test failure, things like "tries accessing the
    network" are simply skipped. Sometimes it is assuming incorrect
    things about the build environment such assuming that stderr is a
    terminal, those are simply skipped. Sometimes test files are removed
    from the tarballs uploaded at crates.io, this appears to be
    intentional, there is a project to remove all such 'bloat',
    disregarding the value of tests -- for those packages we will have
    to switch to git checkouts, but for now I simply disabled tests there.

    I've also found some time bombs (e.g. rust-rustls appears to have a
    certificate expiration problem), there tests are disabled too.

    There were also some genuine test failures, some of them have been
    reported upstream but not all of them yet.
  * antioxidant now has some defenses against bundling -- it detects if
    the feature "bundle", "vendor" or "vendored" is implicitly enabled
    and if so, bails out unless they were explicitly added to the
    package definition.
  * I don't know if I mentioned it previously, but antioxidant now
    supports some 'unstable' rust code even when using 'stable' Rust
    compilers, by setting RUSTC_BOOTSTRAP=1. It's 'not supposed to be
    used', but if it's good enough for the Rust compiler, then it should
    be good enough for other software too, I'd think.

Some questions:

  * Some Rust crates have 'examples' and 'benchmarks' that can be
    compiled and installed. I could teach antioxidant to compile and
    install them, though it appears to provide very little value at cost
    of more compile time and a greater closure size (more binaries, more
    dependencies and wasn't there some bug with grafts whose fix causes
    outputs to be substituted that ended up unused? Though hopefully
    someone could figure out a better fix ...)
  * Due to how regularised the Rust build system is, it's feasible to
    compile tests even when cross-compiling (*), so cross-compiled could
    run the cross-compiled tests on the system they are cross-compiling
    for after the cross-compilation to verify their cross-compiled software.

    Currently, tests are only compiled and installed when #:tests? #true
    which is only the case when compiling natively(*), but with some
    work I could separate building tests from running tests and build
    tests by default when cross-compiling. Downside: tests have to be
    installed in an output, which increases the closure size.

    (Currently tests are installed in an output, but I could change that
    to the working directory).

(*) antioxidant doesn't support cross-compilation yet, but in the past 
I've tried out cross-compiling the standard library and it seemed to 
work, though it wasn't completed.