implement flake support

Author: welteki

Makefile

@@ -23,4 +23,5 @@ test-efi:
 
 install:
 	$(INSTALL) -D bin/nixos-shell $(DESTDIR)$(PREFIX)/bin/nixos-shell
-	$(INSTALL) -D share/nixos-shell/nixos-shell.nix $(DESTDIR)$(PREFIX)/share/nixos-shell/nixos-shell.nix
+	$(INSTALL) -D share/modules/nixos-shell.nix $(DESTDIR)$(PREFIX)/share/modules/nixos-shell.nix
+	$(INSTALL) -D share/nixos-shell.nix $(DESTDIR)$(PREFIX)/share/nixos-shell.nix

bin/nixos-shell

@@ -3,9 +3,11 @@
 set -euo pipefail
 
 script_dir="$(dirname "$(readlink -f "$0")")"
+flake_uri=
+flake_attr=
 
 usage() {
-  echo "USAGE: $0 [--builders builders] [--fallback] [-I path]
+  echo "USAGE: $0 [--builders builders] [--flake uri] [--fallback] [-I path]
 [--impure] [--keep-going | -k] [--keep-failed | -K]
 [--no-net] [--option name value] [--repair]
 [--refresh] [--show-trace] [--verbose | -v | -vv | -vvv | -vvvv | -vvvvv]
@@ -24,6 +26,13 @@ while [[ $# -gt 0 ]]; do
     usage
     exit
     ;;
+  --flake)
+    flake="$(echo "$1" | awk -F '#' '{ print $1; }')"
+
+    flake_uri="$(nix flake metadata --json -- "$flake" | jq -r .url)"
+    flake_attr="$(echo "$1" | awk -F'#' '{ print $2; }')"
+    shift
+    ;;
   -I|--builders)
     j="$1"; shift 1
     extraBuildFlags+=("$i" "$j")
@@ -42,7 +51,6 @@ while [[ $# -gt 0 ]]; do
   esac
 done
 
-export QEMU_NIXOS_CONFIG="$(readlink -f "$nixos_config")"
 unset NIXOS_CONFIG
 
 tempdir=$(mktemp -d)
@@ -51,8 +59,18 @@ cleanup() {
 }
 trap cleanup EXIT SIGINT SIGQUIT ERR
 
-nix-build '<nixpkgs/nixos>' -A vm -k \
-  -I "nixos-config=${script_dir}/../share/nixos-shell/nixos-shell.nix" \
+if [[ -z "$flake_uri" ]]; then
+  extraBuildFlags+=(
+    -I "nixos-config=$nixos_config"
+  )
+else
+  extraBuildFlags+=(
+    --argstr flakeUri "$flake_uri"
+    --argstr flakeAttr "${flake_attr:-"vm"}"
+  )
+fi
+
+nix-build "${script_dir}/../share/nixos-shell.nix" -A "config.system.build.vm" -k \
   -o "${tempdir}/result" \
   "${extraBuildFlags[@]}"
   "$@"

default.nix

@@ -11,8 +11,12 @@ stdenv.mkDerivation {
                  baseNameOf path != ".direnv" &&
                  baseNameOf path != "result"
     ) ./.;
-  buildInputs = [ bash ];
+  nativeBuildInputs = [ makeWrapper ];
   preConfigure = ''
     export PREFIX=$out
   '';
+  postInstall = ''
+    wrapProgram $out/bin/nixos-shell \
+      --prefix PATH : ${lib.makeBinPath [ jq coreutils gawk ]}
+  '';
 }

share/nixos-shell/nixos-shell.nix share/modules/nixos-shell.nixshare/nixos-shell/nixos-shell.nix renamed to share/modules/nixos-shell.nix

@@ -1,15 +1,14 @@
-{ lib, options, config, pkgs, ... }:
+{ lib, options, config, pkgs, modulesPath, ... }:
 
 let
-  nixos_config = builtins.getEnv "QEMU_NIXOS_CONFIG";
   cfg = config.nixos-shell;
 
   mkVMDefault = lib.mkOverride 900;
 in {
-  imports = lib.optional (nixos_config != "") nixos_config ++ [
-    <nixpkgs/nixos/modules/virtualisation/qemu-vm.nix>
+  imports = [
+    "${toString modulesPath}/virtualisation/qemu-vm.nix"
   ];
-
+  
   options.nixos-shell = with lib; {
     mounts = let
       cache = mkOption {

share/nixos-shell.nix

@@ -0,0 +1,26 @@
+{
+  nixpkgs ? <nixpkgs>
+, system ? builtins.currentSystem
+, configuration ? <nixos-config>
+
+, flakeUri ? null
+, flakeAttr ? null
+}:
+let 
+  nixos-shell-module = import ./modules/nixos-shell.nix;
+
+  flake = builtins.getFlake flakeUri;
+  flakeSystem = flake.outputs.packages."${system}".nixosConfigurations."${flakeAttr}" or flake.outputs.nixosConfigurations."${flakeAttr}";
+in
+  if flakeUri != null then
+    flakeSystem.override (attrs: {
+      modules = attrs.modules ++ [ nixos-shell-module ];
+    })
+  else
+    import "${toString nixpkgs}/nixos/lib/eval-config.nix" {
+      inherit system;
+      modules = [
+        configuration
+        nixos-shell-module
+      ];
+    }