Package fails to build with cargo 1.75

[eddelbuettel]

Congratulations on getting a new version to CRAN.

Now. the Ubuntu LTS releases only have rustc and cargo up to version 1.75. The build then fails as follows:

Using cargo 1.75.0
Using rustc 1.75.0 (82e1608df 2023-12-21) (built from a source tarball)
Building for CRAN.
Cleaning previous `src/Makevars`.
Writing `src/Makevars`.
`tools/config.R` has finished.
** libs
using C compiler: ‘gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0’
# Check if NOT_CRAN is false and unzip vendor.tar.xz if so
if [ "" != "true" ]; then \
        if [ -f ./rust/vendor.tar.xz ]; then \
                tar xf rust/vendor.tar.xz && \
                mkdir -p /mnt/build/noble/rshift/src/rshift/src/.cargo && \
                cp rust/vendor-config.toml /mnt/build/noble/rshift/src/rshift/src/.cargo/config.toml; \
        fi; \
fi
export CARGO_HOME=/mnt/build/noble/rshift/src/rshift/src/.cargo && \
export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/root/.cargo/bin" && \
RUSTFLAGS=" --print=native-static-libs" cargo build -j 2 --offline --lib --release --manifest-path=./rust/Cargo.toml --target-dir ./rust/target
error: failed to parse lock file at: /mnt/build/noble/rshift/src/rshift/src/rust/Cargo.lock

Caused by:
  lock file version 4 requires `-Znext-lockfile-bump`
make: *** [Makevars:28: rust/target/release/librshift.a] Error 101
ERROR: compilation failed for package ‘rshift’

The use of 'lock file version 4' implies 1.78 which is not availble. I have been told last week by @JosiahParry that you can circumvent this by setting rust_version = "1.65.0" in you Cargo.toml to not rely on newer features such as lockfile version 4.

This would allow wider distribution of your package so maybe this is something to consider for the next upload.

[JosiahParry]

Thanks, Dirk! @CGMossa and I are hashing out the final bits of a new extendr release and will have some notes for this. You'll be a rust developer on accident soon enough lol!