TL;DR A short guide on how to set environment variables like OPENSSL_DIR within a Guix shell manifest for project-specific development environments.
I run Guix on my laptop and do virtually all my development on it. Guix comes with a beautiful shell environment that allows you to cleanly isolate dependencies for specific projects. Unlike traditional distributions like Debian, Guix does things a little differently, and I sometimes find myself needing to customize the shell environment for specific projects.
Shell Environments
Here’s how you can spawn a Rust development environment:
guix shell rust rust-cargo gcc-toolchain openssl
The problem comes when any crate relies on openssl. The workaround is usually as simple as exporting an environment variable:
export OPENSSL_DIR=$(dirname $(dirname $(realpath $(which openssl))))
Shell Environments from Manifests
This quickly gets repetitive. Luckily, Guix has a nice feature that allows you to write manifests, from which you can spawn shell environments like so:
guix shell -m manifest.scm
A manifest is a simple scheme file that lists all required packages. Here’s an example:
(specifications->manifest '("rust" "rust-cargo" "gcc-toolchain" "openssl"))
Now the idea is simple: why don’t we use that manifest to also set the OPENSSL_DIR environment variable?
After some attempts, I came up with this:
(use-modules (guix profiles)
(guix packages)
(guix search-paths)
(gnu packages rust)
(gnu packages rust-apps)
(gnu packages tls))
;; Create a custom OpenSSL package that exports OPENSSL_DIR pointing to itself
(define openssl-with-env-dir
(package
(inherit openssl)
(name "openssl")
(native-search-paths
(append (package-native-search-paths openssl)
(list (search-path-specification
(variable "OPENSSL_DIR")
(files '("."))
(file-type 'directory)
(separator #f)))))))
;; Create a custom GCC package that exports CC
(define gcc-with-env-cc
(package
(inherit gcc-toolchain)
(name "gcc-toolchain")
(native-search-paths
(append (package-native-search-paths gcc-toolchain)
(list (search-path-specification
(variable "CC")
(files '("bin/gcc"))
(file-type 'regular)
(separator #f)))))))
(packages->manifest
(list rust
rust-cargo
gcc-with-env-cc
openssl-with-env-dir))
When you spawn a shell from this manifest, OPENSSL_DIR will point to the correct location.
Conclusion
Guix can get in the way sometimes, but if you have some patience to learn, these are one-time problems.