The goal of this project is to simplify per-project developer environments.

Imagine, a new employee joins the company, or somebody transfers teams, or somebody wants to contribute to one of your Open Source projects. It should take them 10 minutes to clone the repo and get all of the development dependencies.

See docs (docs source)

Keep it compatible with:

• nix-shell
• direnv
• nix flakes

pkgs.stdenv.mkDerivation and pkgs.mkShell build on top of the pkgs.stdenv which introduces all sort of dependencies. Each added package, like the pkgs.go in the "Story time!" section has the potential of adding new environment variables, which then need to be unset. The stdenv itself contains either GCC or Clang which makes it hard to select a specific C compiler.

This is why mkShell builds its environment from a builtins.derivation.

direnv loads will change from:

direnv: export +AR +AS +CC +CONFIG_SHELL +CXX +HOST_PATH +IN_NIX_SHELL +LD +NIX_BINTOOLS +NIX_BINTOOLS_WRAPPER_TARGET_HOST_x86_64_unknown_linux_gnu +NIX_BUILD_CORES +NIX_BUILD_TOP +NIX_CC +NIX_CC_WRAPPER_TARGET_HOST_x86_64_unknown_linux_gnu +NIX_CFLAGS_COMPILE +NIX_ENFORCE_NO_NATIVE +NIX_HARDENING_ENABLE +NIX_INDENT_MAKE +NIX_LDFLAGS +NIX_STORE +NM +OBJCOPY +OBJDUMP +RANLIB +READELF +RUSTC +SIZE +SOURCE_DATE_EPOCH +STRINGS +STRIP +TEMP +TEMPDIR +TMP +TMPDIR +buildInputs +buildPhase +builder +builtDependencies +cargo_bins_jq_filter +cargo_build_options +cargo_options +cargo_release +cargo_test_options +cargoconfig +checkPhase +configureFlags +configurePhase +cratePaths +crate_sources +depsBuildBuild +depsBuildBuildPropagated +depsBuildTarget +depsBuildTargetPropagated +depsHostHost +depsHostHostPropagated +depsTargetTarget +depsTargetTargetPropagated +doCheck +doInstallCheck +docPhase +dontAddDisableDepTrack +dontUseCmakeConfigure +installPhase +name +nativeBuildInputs +out +outputs +patches +preInstallPhases +propagatedBuildInputs +propagatedNativeBuildInputs +remapPathPrefix +shell +src +stdenv +strictDeps +system +version ~PATH

to:

direnv: export +DEVSHELL_DIR +PRJ_DATA_DIR +PRJ_ROOT +IN_NIX_SHELL +NIXPKGS_PATH ~PATH

There are new environment variables useful to support the day-to-day activities:

• DEVSHELL_DIR: contains all the programs.
• PRJ_ROOT: points to the project root.
• PRJ_DATA_DIR: points to $PRJ_ROOT/.data by default. Is used to store runtime data.
• NIXPKGS_PATH: path to nixpkgs source.

The shell comes pre-loaded with some utility functions. I'm not 100% sure if those are useful yet:

• menu - list all the programs available

When entering a random project, it's useful to get a quick view of what commands are available.

When running nix-shell or nix develop, mkShell prints a welcome message:

🔨 Welcome to devshell

[[general commands]]

  hello         - prints hello
  menu          - prints this menu

[formatters]

  nixpkgs-fmt   - Nix code formatter for nixpkgs

[linters]

  golangci-lint - golang linter

[utilites]

  hub           - github utility

[devshell]$ 

You might be passionate about Nix, but people on the team might be afraid of that non-mainstream technology. So let them write TOML instead. It should handle 80% of the use-cases and falling back on Nix is always possible.

Life is not complete otherwise. Huhu.

Packages that contain bash completions will automatically be loaded by mkShell in nix-shell or nix develop modes.

With a CI + Binary cache setup, one often wants to be able to capture all the build inputs of a shell.nix. With mkShell capturing all of the development dependencies is as easy as:

nix-build shell.nix | cachix push <mycache>

Devshells are runnable (via nix run). This makes it possible to run commands defined in your devshell without entering a nix-shell or nix develop session:

nix run '.#<myapp>' -- <devshell-command> <and-args>

This project itself exposes a Nix application; you can try it out with:

nix run 'github:numtide/devshell' -- hello

See here for more details.

A lot of things!

• Documentation
  • Explain how all of this works and all the use-cases.
• Testing
  • Write integration tests for all of the use-cases.
• Lazy dependencies
  • This requires some coordination with the repository structure. To keep the dev closure small, it would be nice to be able to load some of the dependencies on demand.
• Doctor / nix version check
  • Not everything can be nicely sandboxed. Is it possible to get a fast doctor script that checks that everything is in good shape?
• Support other shells
  • What? Not everyone is using bash? Right now, support is already available in direnv mode.

1. Change files in docs/
2. Run nix run .#docs
3. Open docs

1. See benchmark/README.md
2. Run nix run .#bench

Looking for help or customization?

Get in touch with Numtide to get a quote. We make it easy for companies to work with Open Source projects: https://numtide.com/contact