Error messages for bad cargo/rust environment during PEP517 install

[ijl]

The error output from pip is otherwise not understandable by
a user who does not know this package needs Rust or what Rust is.

Installing build dependencies ... done
Getting requirements to build wheel ... done
Preparing wheel metadata ... error
ERROR: Complete output from command ... pip/_vendor/pep517/_in_process.py prepare_metadata_for_build_wheel ...
ERROR: 💥 pyo3-pack failed
Cargo metadata failed: No such file or directory (os error 2)
...
subprocess.CalledProcessError: Command '['pyo3-pack', 'pep517', 'write-dist-info', ... ' returned non-zero exit status 1

#2

[ijl]

I don't know whether all bindings require nightly. If so that is something to check as well.

[konstin]

Great idea, thank you!

I don't know whether all bindings require nightly. If so that is something to check as well.

Only pyo3 requires nightly. pyo3 already prints an understandable error message, even though it might be better to check this earlier:

process didn't exit successfully: `/home/konsti/pyo3/target/debug/build/pyo3-46d57cafcc76894a/build-script-build` (exit code: 101)
--- stderr
Error: pyo3 requires a nightly or dev version of Rust.
Installed version is: 1.35.0 (2019-05-20). Minimum required: 1.34.0-nightly (2019-02-06).
thread 'main' panicked at 'Aborting compilation due to incompatible compiler.', build.rs:556:17
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.