fetchPnpmDeps: don't fail on empty lockfile

If the lockfile is empty, no files will be put in the output directory. 
In this case, the find invocations produce an empty list of results. 
xargs' default behaviour is to always invoke its command at least once; 
if its input is empty, then its command will not be passed any 
filenames. This produces an invocation like `chmod 555`. chmod, however, 
fails in this case, expecting an operand. So we need to tell xargs not 
to invoke its command at all in the case of empty input.

pkgs/build-support/node/fetch-pnpm-deps/default.nix

@@ -162,9 +162,9 @@ in
               # See https://github.com/NixOS/nixpkgs/pull/350063
               # See https://github.com/NixOS/nixpkgs/issues/422889
               if [[ ${toString fetcherVersion} -ge 2 ]]; then
-                find $storePath -type f -name "*-exec" -print0 | xargs -0 chmod 555
-                find $storePath -type f -not -name "*-exec" -print0 | xargs -0 chmod 444
-                find $storePath -type d -print0 | xargs -0 chmod 555
+                find $storePath -type f -name "*-exec" -print0 | xargs --no-run-if-empty -0 chmod 555
+                find $storePath -type f -not -name "*-exec" -print0 | xargs --no-run-if-empty -0 chmod 444
+                find $storePath -type d -print0 | xargs --no-run-if-empty -0 chmod 555
               fi
 
               if [[ ${toString fetcherVersion} -ge 3 ]]; then

pkgs/test/default.nix

@@ -170,6 +170,8 @@ in
 
   php = recurseIntoAttrs (callPackages ./php { });
 
+  pnpm = recurseIntoAttrs (callPackages ./pnpm { });
+
   go = recurseIntoAttrs (callPackage ../build-support/go/tests.nix { });
 
   lake = callPackage ../build-support/lake/test { };

pkgs/test/pnpm/default.nix

@@ -0,0 +1,4 @@
+{ callPackage }:
+{
+  pnpm-empty-lockfile = callPackage ./pnpm-empty-lockfile { };
+}

pkgs/test/pnpm/pnpm-empty-lockfile/default.nix

@@ -0,0 +1,32 @@
+{
+  pkgs,
+  stdenv,
+  fetchPnpmDeps,
+  nodejs,
+  pnpm_10,
+  pnpmConfigHook,
+}:
+stdenv.mkDerivation {
+  name = "pnpm-empty-lockfile";
+
+  src = ./.;
+
+  nativeBuildInputs = [
+    pnpm_10
+    pnpmConfigHook
+  ];
+
+  pnpmDeps = fetchPnpmDeps {
+    pname = "pnpm-empty-lockfile";
+    fetcherVersion = 3;
+    pnpm = pnpm_10;
+    src = ./.;
+    hash = "sha256-u0GOAX5B1f2ANWbOezScp/eKQRRZA/JoYfQ5zLrNip4=";
+  };
+
+  buildPhase = ''
+    runHook preBuild
+    touch $out
+    runHook postBuild
+  '';
+}

pkgs/test/pnpm/pnpm-empty-lockfile/package.json

@@ -0,0 +1,6 @@
+{
+    "name": "pnpm-empty-lockfile",
+    "main": "main.mjs",
+    "dependencies": {
+    }
+}

pkgs/test/pnpm/pnpm-empty-lockfile/pnpm-lock.yaml

@@ -0,0 +1,9 @@
+lockfileVersion: '9.0'
+
+settings:
+  autoInstallPeers: true
+  excludeLinksFromLockfile: false
+
+importers:
+
+  .: {}