init: devshell for hands-on onboarding

devshell.toml

@@ -0,0 +1,19 @@
+[devshell]
+name = "nixpkgs"
+packages = [
+  "fd",
+  "nixpkgs-fmt",
+]
+
+[[commands]]
+name = "fmt"
+help = "Check Nix formatting"
+category = "folder tree checks"
+command = "nixpkgs-fmt ${@} ."
+
+[[commands]]
+name = "evalnix"
+help = "Check Nix parsing"
+category = "folder tree checks"
+command = "fd --extension nix --exec nix-instantiate --parse --quiet {} >/dev/null"
+

flake.nix

@@ -63,6 +63,11 @@
       });
 
       checks.x86_64-linux.tarball = jobs.tarball;
+      devShell = {
+        x86_64-linux = import ./shell.nix { system = "x86_64-linux"; };
+        x86_64-darwin = import ./shell.nix { system = "x86_64-darwin"; };
+        aarch64-linux = import ./shell.nix { system = "aarch64-linux"; };
+      };
 
       htmlDocs = {
         nixpkgsManual = jobs.manual;

shell.nix

@@ -0,0 +1,17 @@
+{ system ? builtins.currentSystem }:
+let
+  # nixpkgs / devshell is only used for development. Don't add it to the flake.lock.
+  devshellGitRev = "709fe4d04a9101c9d224ad83f73416dce71baf21";
+
+  nixpkgsSrc = ./.;
+
+  devshellSrc = fetchTarball {
+    url = "https://github.com/numtide/devshell/archive/${devshellGitRev}.tar.gz";
+    sha256 = "1px9cqfshfqs1b7ypyxch3s3ymr4xgycy1krrcg7b97rmmszvsqr";
+  };
+
+  pkgs = import nixpkgsSrc { inherit system; };
+  devshell = import devshellSrc { inherit system pkgs; };
+
+in
+devshell.fromTOML ./devshell.toml