Update snapshot to avoid rust-lang/cargo#976, which otherwise breaks the
build.
Also move the `cargoSnapshot` derivation inside a set in
pkgs/top-level/all-packages.nix in order to hide the `cargo-snapshot`
packages from `nix-env -qa`, since it's only used to build the `cargo`
package.
This happened in VM builds:
make flags: SHELL=/nix/store/dbxpkswwc7rh6g1iy6dwqklzw39hihb1-bash-4.3-p33/bin/bash
/nix/store/jm26xg0h3jcrg4bbrwiqx3jpirscdk0p-stdenv/setup: line 658: 5957 Segmentation fault make ${makefile:+-f $makefile} ${enableParallelBuilding:+-j${NIX_BUILD_CORES} -l${NIX_BUILD_CORES}} $makeFlags "${makeFlagsArray[@]}" $buildFlags "${buildFlagsArray[@]}"
Instead, discover it automatically when building the package.
This makes `buildRustPackage` more future-proof with respect to changes
in how `cargo` generates the hash.
Also, it fixes broken builds in i686 because apparently, cargo generates
a different registry index hash in this architecture (compared to
x86-64).
It seems that when you pass `leaveDotGit = true` to `fetchgit`, sometimes
the output can still change (i.e. it's not completely deterministic).
This could be due to changes in the upstream git repository...
This makes buildRustPackage portable to non-Linux platforms.
Additionally, now we also save the `Cargo.lock` file into the fetch output, so
that we don't have to run $cargoUpdateHook again just before building.
Instead, move that code into buildRustPackage.
The setup hook was only doing part of the work anyway, and having it in
a separate place was obscuring what was really going on.
It turns out that `cargo`, with respect to registry dependencies, was
ignoring the package versions locked in `Cargo.lock` because we changed
the registry index URL.
Therefore, every time `rustRegistry` would be updated, we'd always try
to use the latest version available for every dependency and as a result
the deps' SHA256 hashes would almost always have to be changed.
To fix this, now we do a string substitution in `Cargo.lock` of the
`crates.io` registry URL with our URL. This should be safe because our
registry is just a copy of the `crates.io` registry at a certain point
in time.
Since now we don't always use the latest version of every dependency,
the build of `cargo` actually started to fail because two of the
dependencies specified in its `Cargo.lock` file have build failures.
To fix the latter problem, I've added a `cargoUpdateHook` variable that
gets ran both when fetching dependencies and just before building the
program. The purpose of `cargoUpdateHook` is to do any ad-hoc updating
of dependencies necessary to get the package to build. The use of the
'--precise' flag is needed so that cargo doesn't try to fetch an even
newer version whenever `rustRegistry` is updated (and therefore have to
change depsSha256 as a consequence).
