Merge pull request #1018 from Atry/no-impure

Avoid --impure in flake-parts based projects

Author: domenkozar

devenv.nix

@@ -81,13 +81,13 @@
       nix flake init --template ''${DEVENV_ROOT}#flake-parts
       nix flake update \
         --override-input devenv ''${DEVENV_ROOT}
-      nix develop --accept-flake-config --impure --command echo nix-develop started succesfully |& tee ./console
+      nix develop --accept-flake-config --override-input devenv-root "file+file://"<(printf %s "$PWD") --command echo nix-develop started succesfully |& tee ./console
       grep -F 'nix-develop started succesfully' <./console
       grep -F "$(${lib.getExe pkgs.hello})" <./console
       # Test that a container can be built
       if $(uname) == "Linux"
       then
-        nix build --impure --accept-flake-config --show-trace .#container-processes
+        nix build --override-input devenv-root "file+file://"<(printf %s "$PWD") --accept-flake-config --show-trace .#container-processes
       fi
     popd
     rm -rf "$tmp"

templates/flake-parts/.envrc

@@ -5,7 +5,8 @@ fi
 nix_direnv_watch_file devenv.nix
 nix_direnv_watch_file devenv.lock
 nix_direnv_watch_file devenv.yaml
-if ! use flake . --impure
+
+if ! use flake . --override-input devenv-root "file+file://"<(printf %s "$PWD")
 then
   echo "devenv could not be built. The devenv environment was not loaded. Make the necessary changes to devenv.nix and hit enter to try again." >&2
 fi

templates/flake-parts/flake.nix

@@ -2,6 +2,10 @@
   description = "Description for the project";
 
   inputs = {
+    devenv-root = {
+      url = "file+file:///dev/null";
+      flake = false;
+    };
     nixpkgs.url = "github:cachix/devenv-nixpkgs/rolling";
     devenv.url = "github:cachix/devenv";
     nix2container.url = "github:nlewo/nix2container";
@@ -14,7 +18,7 @@
     extra-substituters = "https://devenv.cachix.org";
   };
 
-  outputs = inputs@{ flake-parts, ... }:
+  outputs = inputs@{ flake-parts, devenv-root, ... }:
     flake-parts.lib.mkFlake { inherit inputs; } {
       imports = [
         inputs.devenv.flakeModule
@@ -33,6 +37,12 @@
         packages.default = pkgs.hello;
 
         devenv.shells.default = {
+          devenv.root =
+            let
+              devenvRootFileContent = builtins.readFile devenv-root.outPath;
+            in
+            pkgs.lib.mkIf (devenvRootFileContent != "") devenvRootFileContent;
+
           name = "my-project";
 
           imports = [