draft: package c2rust as a "nix flake"

[mstone]

Nix flakes are an emerging technology for composing software which solves a related but complementary problem to the one addressed today via c2rust's shell.nix/nix-shell support.

This PR provides a rough-draft-quality flake for c2rust. Notable future work includes:

• testing. So far, I have only tested it on aarch64-darwin, where it works as expected so far, and is able to transpile and run the demo for my current subject of interest, osqp.
• wider platform support. While untested so far, I expect builds to fail on x86_64-linux at least due to support offline build #356.

The benefit is that flakes enable easy building, development, and usage of c2rust with pinned, shareable, but still easily editable LLVM, clang, and rust toolchain versions via convenient commands like

• nix build
• nix shell
• etc.

or with URI-like "flake-refs" (which also support naming specific branches/commits/...) like:

• nix build github:mstone/c2rust,
• nix shell github:mstone/c2rust,
• nix run github:mstone/c2rust, or
• nix profile install github:mstone/c2rust

or their upstream equivalents, if merged.

[theduke]

Great to see this.

I would recommend not committing the flake.lock in the repo and leave the nixpkgs dependency as ephemeral so you don't have to do nix shell --no-write-lock-file --recreate-lock-file github:mstone/c2rust to avoid pulling in a whole separate set of nix packages.

ps: #328 can be closed when this is merged.

[theduke]

@mstone building currently fails because the build tries to download some dependencies.

            status_string: "Couldn't resolve host name"
            log:
            --- LOG BEGIN ---
            Could not resolve host: github.com

    Closing connection 0



            --- LOG END ---
            error: downloading 'https://github.com/intel/tinycbor/archive/v0.5.3.tar.gz' failed
            status_code: 6
            status_string: "Couldn't resolve host name"
            log:
            --- LOG BEGIN ---
            Could not resolve host: github.com

    Closing connection 0



            --- LOG END ---
            error: downloading 'https://github.com/intel/tinycbor/archive/v0.5.3.tar.gz' failed
            status_code: 6
            status_string: "Couldn't resolve host name"
            log:
            --- LOG BEGIN ---
            Could not resolve host: github.com

    Closing connection 0



            --- LOG END ---
            error: downloading 'https://github.com/intel/tinycbor/archive/v0.5.3.tar.gz' failed
            status_code: 6
            status_string: "Couldn't resolve host name"
            log:
            --- LOG BEGIN ---
            Could not resolve host: github.com

    Closing connection 0



            --- LOG END ---




  make[3]: *** [CMakeFiles/tinycbor_build.dir/build.make:98: tinycbor/src/tinycbor_build-stamp/tinycbor_build-download] Error 1
  make[2]: *** [CMakeFiles/Makefile2:91: CMakeFiles/tinycbor_build.dir/all] Error 2
  make[1]: *** [CMakeFiles/Makefile2:254: CMakeFiles/clangAstExporter.dir/rule] Error 2
  make: *** [Makefile:202: clangAstExporter] Error 2
  thread 'main' panicked at '
  command did not execute successfully, got: exit status: 2

[milahu]

fwiw, my c2rust.nix draft from 2 months ago
i had to set some envs so the builder would find clang and llvm
i used tinycbor from nix as shown in #356

[HKalbasi]

The current shell.nix doesn't work for me (#1045), neither the flake included in this PR.

Does anyone in this thread knows how to build c2rust on nix?