Scheduled to be released on 2021-10-21.
https://internals.rust-lang.org/t/rust-1-56-0-pre-release-testing/15459
https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1560-2021-10-21
Including changes to USES=cargo for https://bugs.freebsd.org/256581
```
Uses/cargo: Rework git source support based on patch-in-config sections
Git sources from `Cargo.lock` are added to `CARGO_CRATES` through
the normal mechanism of `make cargo-crates` by the porter. They
are used to populate `MASTER_SITES`, `DISTFILES` with static
git-archive(1) tarballs a la `USE_GITHUB`, `USE_GITLAB`. In the
configure phase we generate `[patch]` sections in the config file
which will cause `cargo update` to auto-update `Cargo.lock` to point
to the appropriate extraction directories.
Normally `cargo update` would connect to the network to update all
Git sources but since rust-1.55.0 our cargo has been patched to
skip this when `CARGO_FREEBSD_PORTS_SKIP_GIT_UPDATE` is set in the
environment.
This replaces the old `CARGO_USE_GITHUB`, `CARGO_USE_GITLAB` hacks
where this was done by editing all `Cargo.toml` with sed(1) calls.
Additionally, we try to automatically infer the individiual crate
sub-directories inside the Git sources based on `package.name` in
`Cargo.toml` to remove the need for `CARGO_GIT_SUBDIR`.
USES=cargo also now sets `WRKSRC_crate_$name` for each crate to
point to the crate extraction directories.
```