build-support/node/import-npm-lock: use structuredAttrs instead of passAsFile

pkgs/build-support/node/import-npm-lock/default.nix

@@ -12,6 +12,7 @@ let
     match
     elemAt
     toJSON
+    toFile
     removeAttrs
     ;
   inherit (lib) importJSON mapAttrs;
@@ -157,18 +158,15 @@ lib.fix (self: {
       {
         inherit pname version;
 
-        passAsFile = [
-          "package"
-          "packageLock"
-        ];
+        package = toFile (toJSON packageJSON');
+        packageLock = toFile (toJSON packageLock');
 
-        package = toJSON packageJSON';
-        packageLock = toJSON packageLock';
+        __structuredAttrs = true;
       }
       ''
         mkdir $out
-        cp "$packagePath" $out/package.json
-        cp "$packageLockPath" $out/package-lock.json
+        cp "${package}" > $out/package.json
+        cp "${packageLock}" > $out/package-lock.json
       '';
 
   # Build node modules from package.json & package-lock.json
@@ -180,6 +178,11 @@ lib.fix (self: {
       nodejs,
       derivationArgs ? { },
     }:
+    let
+      # Backwards compatibility: if derivationArgs contains passAsFile,
+      # we can't force structuredAttrs here yet.
+      __structuredAttrs = !(derivationArgs ? passAsFile);
+    in
     stdenv.mkDerivation (
       {
         pname = derivationArgs.pname or "${getName package}-node-modules";
@@ -213,17 +216,29 @@ lib.fix (self: {
         ++ lib.optionals stdenv.hostPlatform.isDarwin [ cctools ]
         ++ derivationArgs.nativeBuildInputs or [ ];
 
+        postPatch =
+          (
+            if __structuredAttrs then
+              ''
+                echo -n "$package" > package.json
+                echo -n "$packageLock" > package-lock.json
+              ''
+            else
+              ''
+                cp --no-preserve=mode "$packagePath" package.json
+                cp --no-preserve=mode "$packageLockPath" package-lock.json
+              ''
+          )
+          + derivationArgs.postPatch or "";
+
+        inherit __structuredAttrs;
+      }
+      // lib.optionalAttrs (!__structuredAttrs) {
         passAsFile = [
           "package"
           "packageLock"
         ]
-        ++ derivationArgs.passAsFile or [ ];
-
-        postPatch = ''
-          cp --no-preserve=mode "$packagePath" package.json
-          cp --no-preserve=mode "$packageLockPath" package-lock.json
-        ''
-        + derivationArgs.postPatch or "";
+        ++ derivationArgs.passAsFile;
       }
     );