raingloom schreef op wo 06-04-2022 om 00:28 [+0200]:
> I'm also a bit worried with the trend of Guix trying to duplicate
> functionality already present in language package managers and config
> file formats. It creates a two-sources-of-truth situation.

For service configurations, there is only one source of truth: the
configuration record.  It just happens to be converted to another
format.  The underlying file format, TOML is not Cargo-specific
(https://toml.io/en/) and parsed with python-toml, presumably python-
toml parses it correctly.  (Whether antioxidant-build-system interprets
it correctly, is of course a different matter.)

Also, Cargo is both a package manager and a build system.  The package
manager part is useless to Guix, we even have to work-around it (see
e.g. patch-cargo-checksums, crate-closure).  Unfortunately, there does
not seem to be a way to only use the build system part of Cargo and
ignore the package manager part, so the build system part has to be
reimplemented ...

> Trying to keep one up to date with the other can be an issue, this is why I
> didn't create a custom record type for Yggdrasil config files and just
> used a generic JSON converter. Which paid off, since there were in fact
> changes in the config fields between versions.

The configuration record fields does not have to support every new
thing, it just haves to be _sufficiently_ up to date for users.  And if
a configuration field that's needed is missing, then it's almost
trivial to add it.

Additionally, some services have an 'extra-content' escape hatch. 
yggrasil-configuration could have one too, then the user could have
both write most things as Scheme (benefit: largely unified interface,
more automation possible) _and_ be able to use the latest features not
yet directly supported by the configuraiton fields, via the escape
hatch.

> Will this build system avoid that issue as well?

antioxidant-build-system is a build system, not a configuration format.

I've found that most Cargo.toml are rather tame.  They often just set:

  * name
  * Some metadata like version, authors, home-page, include, exclude
    ... that antioxidant-build-system doesn't need.
  * sometimes 'build' or 'path'
  * dependencies  / dev-dependencies / build-dependencies, also
    unneeded by antioxidant-build-system (the importer might need them,
    but that's a separate component)

Looking at <https://doc.rust-lang.org/cargo/reference/manifest.html>,
there are some more things are things that antioxidant-build-system
doesn't need:

  * resolver
  * badges, [[bench]]
  * the [patch] and [replace]  --- just use a variant package in the
    package inputs

Now, there are some things that aren't yet supported by antioxidant-
build-system but probably need to be:

  * autobins / autoexamples / autotests / [lib] / [bin] / [example]
    / [links]
  * setting various environment variables before build.rs
    (there's probably some list somewhere ...)

But aside from that, it seems that the essential parts of Cargo.toml
are rather tame and unlikely to be added to.  And if something
essential is added anyway and needs to be supported, then it should be
easy to modify antioxidant-build-system appropriately (long-term)
and/or work-around it by setting some environment variables locally or
maybe some substitute* (short-term).

> I guess if the data it operates on has truly stable semantics, then
> writing an independent implementation is not as big a problem, since
> once written and debugged, it won't need to change.
> (And getting rid of cargo would be nice for Rust dev on Guix.)

AFAICT, the parts important to Guix are sufficiently stable -- not
immutable (sometimes changes do happen).  And even if it was unstable,
it still seems much better than just using Cargo (due to much shorter
build times, less strict about versions, not having to add winapi
crates when compiling for Linux, no copying tarballs around, no
#:cargo-inputs instead of [propagated-]inputs ...).

Greetings,
Maxime.