[WIP] nix flake

[nejucomo]

WIP == Work In Progress

I'm in the midst of creating a flake.nix file so that all zingolib crates can be build and tested on any machine with nix.

[nejucomo]

One reason I like nix is that it codifies all dependencies. Compare the current flake.nix specification of non-cargo dependencies to README.md Pre-requisites.

The nix version is automated and verified on every (nix) build or (nix) test target, and it demonstrates that git is also a prerequisite that's not in the README.md.

[nejucomo]

The current blocker for nix build is that it appears zcash_client_backend has a build script which attempts to write into its source directory (example).

By default in nix all source must be read-only because it has deterministic builds as a top-line goal. A potential work-around in this branch would be to tell the nix build process to copy the zcash_client_backend source to a temporary read/write directory when building.

However, a cleaner solution is to fix zcash_client_backend not to do this anti-pattern. I'm currently investigating the latter. I consider it an antipattern to conflate the output of hopefully reproducible automation such as protoc with human-edited revision controlled source, but presumably zcash_client_backend does this as a work-around for some limitation in protoc.

[nejucomo]

I filed zcash/librustzcash#1420 to track my preferred upstream fix which I consider cleanest. If that remains a blocker, the work-around fix within the nix build process is possible.

[nejucomo]

I implemented the nix-build work-around for the zcash/librustzcash#1420 issue because it felt quicker.

Now the new blocker is:

cargo-package> error: failed to run custom build command for `darkside-tests v0.1.0 (/build/source/darkside-tests)`
cargo-package> Caused by:
cargo-package>   process didn't exit successfully: `/build/source/target/release/build/darkside-tests-e0fd5ded20d526db/build-script-build` (exit status: 1)
cargo-package>   --- stdout
cargo-package>   cargo:rerun-if-changed=../zingo-testutils/proto/compact_formats.proto
cargo-package>   cargo:rerun-if-changed=proto/darkside.proto
cargo-package>   cargo:rerun-if-changed=../zingo-testutils/proto/service.proto
cargo-package>   cargo:rerun-if-changed=proto
cargo-package>   cargo:rerun-if-changed=../zingo-testutils/proto
cargo-package>   --- stderr
cargo-package>   Error: Custom { kind: Other, error: "protoc failed: Could not make proto path relative: ../zingo-testutils/proto/compact_formats.proto: No such file or directory\n" }
cargo-package> warning: build failed, waiting for other jobs to finish...

I am pausing work on this and haven't diagnosed this, but at first glance it looks like a build script is assuming crates are placed identically to the git source. I do not know why this would be violated in the nix build, but I'll see if I can remove that assumption from the build script. If not, I'll see about patching the nix build somehow to meet the assumption.

[zancas]

Is this still in progress?