Try #1649:

Author: iohk-bors[bot]

default.nix

@@ -1,16 +1,19 @@
 {...}@args:
 
 let
+  pins = (__fromJSON (__readFile ./flake.lock)).nodes;
+  nixpkgsPin = pins.nixpkgs-2205.locked;
+  flakeCompatPin = pins.flake-compat.locked;
   nixpkgsSrc =
     builtins.fetchTarball {
-      url = "https://github.com/NixOS/nixpkgs/archive/110a2c9ebbf5d4a94486854f18a37a938cfacbbb.tar.gz";
-      sha256 = "sha256-leWXLchbAbqOlLT6tju631G40SzQWPqaAXQG3zH1Imw=";
+      url = "https://github.com/NixOS/nixpkgs/archive/${nixpkgsPin.rev}.tar.gz";
+      sha256 = nixpkgsPin.narHash;
     };
   pkgs = args.pkgs or (import nixpkgsSrc {});
   flake-compat =
     pkgs.fetchzip {
-      url = "https://github.com/edolstra/flake-compat/archive/5523c47f13259b981c49b26e28499724a5125fd8.tar.gz";
-      sha256 = "sha256-7IySNHriQjzOZ88DDk6VDPf1GoUaOrOeUdukY62o52o=";
+      url = "https://github.com/edolstra/flake-compat/archive/{flakeCompatPin.rev}.tar.gz";
+      sha256 = flakeCompatPin.narHash;
     };
   self = import flake-compat {
     # We bypass flake-compat's rootSrc cleaning by evading its detection of this as a git

flake.lock

@@ -8,6 +8,7 @@
     nixpkgs-2111 = { url = "github:NixOS/nixpkgs/nixpkgs-21.11-darwin"; };
     nixpkgs-2205 = { url = "github:NixOS/nixpkgs/nixpkgs-22.05-darwin"; };
     nixpkgs-unstable = { url = "github:NixOS/nixpkgs/nixpkgs-unstable"; };
+    flake-compat = { url = "github:hamishmack/flake-compat/hkm/pkgs-fetch"; flake = false; };
     flake-utils = { url = "github:numtide/flake-utils"; };
     hydra.url = "hydra";
     hackage = {

flake.nix

@@ -39,6 +39,8 @@ fi
 
 if [ "$TESTS" == "unit-tests" ] || [ "$TESTS" == "all" ]; then
   printf "*** Running the unit tests... " >& 2
+  # Running nix build first avoids `error: path '/nix/store/X-hackage-to-nix-ghcjs-overlay.drv' is not valid`
+  nix-build ./default.nix --argstr compiler-nix-name $GHC -A unit.tests
   res=$(nix-instantiate --eval --json --strict ./default.nix --argstr compiler-nix-name $GHC -A unit.tests)
   num_failed=$(jq length <<< "$res")
   if [ $num_failed -eq 0 ]; then