Maybe back when .cargo/config.in was added, the directory indicated for
vendored crates needed to be absolute. That is at least not the case
with the current supported versions of rust.
The current setup has a few caveats:
- .cargo/config.in has shown to become stale (it currently contains
multiple unused entries)
- non-gecko build tasks have to generate a .cargo/config on their own if
they want to use vendored crates
- in turn, non-gecko build tasks that don't, may unknowingly get their
dependencies from crates.io (see the recent attempt at moving
geckodriver builds to a separate task).
By checking in a .cargo/config file, we can alleviate the last two, but
that comes at the price of `cargo update` not wanting to act when
.cargo/config exists, because of the source replacement configuration.
But rust vendor gently generates a suitable configuration on its own, so
we can use that to generate a .cargo/config automatically. Which
addresses the first caveat of the current setup. That leaves us with
`cargo update` not working out of the box, but that just requires people
running it to manually remove .cargo/config first. Which is arguably
what rust wants you to do in the first place. It's kind of incidental
that we started with a .cargo/config.in rather than .cargo/config.
Now, while a simple .cargo/config works, that's not enough for the case
where the objdir doesn't live inside the source directory. In that case
cargo looks for the configuration from the objdir, and fails to find it.
So we still need a .cargo/config.in, which we generate with a little
trick.
Differential Revision: https://phabricator.services.mozilla.com/D43012
--HG--
rename : .cargo/config.in => .cargo/config
extra : moz-landing-system : lando
Benjamin Bouvier
Mike Hommey