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In the current state of our Rust code base we don't really have any
requirements for the minimum supported Rust version yet, as we don't use
any features introduced by a recent version of Rust. Consequently, we
have decided that we want to aim for a rather old version and edition of
Rust, where the hope is that using an old version will make alternatives
like gccrs viable earlier for compiling Git.
But while we specify the Rust edition, we don't yet specify a Rust
version. And even if we did, the Rust version would only be enforced for
our own code, but not for any of our dependencies.
We don't yet have any dependencies at the current point in time. But
let's add some safeguards by specifying the minimum supported Rust
version and using cargo-msrv(1) to verify that this version can be
satisfied for all of our dependencies.
Note that we fix the version of cargo-msrv(1) at v0.18.1. This is the
latest release supported by Ubuntu's Rust version.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Add the infrastructure into Meson to build an internal Rust library.
Building the Rust parts of Git are for now entirely optional, as they
are mostly intended as a test balloon for both Git developers, but also
for distributors of Git. So for now, they may contain:
- New features that are not mission critical to Git and that users can
easily live without.
- Alternative implementations of small subsystems.
If these test balloons are successful, we will eventually make Rust a
mandatory dependency for our build process in Git 3.0.
The availability of a Rust toolchain will be auto-detected by Meson at
setup time. This behaviour can be tweaked via the `-Drust=` feature
toggle.
Next to the linkable Rust library, also wire up tests that can be
executed via `meson test`. This allows us to use the native unit testing
capabilities of Rust.
Note that the Rust edition is currently set to 2018. This edition is
supported by Rust 1.49, which is the target for the upcoming gcc-rs
backend. For now we don't use any features of Rust that would require a
newer version, so settling on this old version makes sense so that
gcc-rs may become an alternative backend for compiling Git. If we _do_
want to introduce features that were added in more recent editions of
Rust though we should reevaluate that choice.
Inspired-by: Ezekiel Newren <ezekielnewren@gmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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