Fix 'argument list too long' during build

src/tmpl/yarn-project.nix.in

@@ -1,7 +1,7 @@
 # This file is generated by running "yarn install" inside your project.
 # Manual changes might be lost - proceed with caution!
 
-{ lib, coreutils, nodejs, stdenv }: src:
+{ lib, coreutils, nodejs, stdenv, writeText }: src:
 
 let
 
@@ -28,9 +28,11 @@ let
   };
 
   # Shell snippet to collect all project dependencies.
-  collectCache = lib.concatMapStrings (args: ''
-    cp ${fetchOne args} '${args.filename}'
-  '') cacheEntries;
+  collectCacheScript = writeText "collect-cache.sh" (
+    lib.concatMapStrings (args: ''
+      cp ${fetchOne args} '${args.filename}'
+    '') cacheEntries
+  );
 
 in stdenv.mkDerivation {
   name = @@PROJECT_NAME@@;
@@ -60,7 +62,7 @@ in stdenv.mkDerivation {
     rm -fr '${cacheFolder}'
     mkdir -p '${cacheFolder}'
     pushd '${cacheFolder}' > /dev/null
-    ${collectCache}
+    source ${collectCacheScript}
     popd > /dev/null
 
     # Store the absolute path to Yarn for the 'yarn' alias.