fetch-cargo-deps: factor into fetchCargoDeps function

pkgs/build-support/rust/fetch-cargo-deps

@@ -1,7 +1,4 @@
-source $stdenv/setup
-
-set -euo pipefail
-
+fetchCargoDeps() {
     src=$(realpath $1)
     out=$(realpath $2)
 
@@ -34,11 +31,9 @@ fi
 
     # We need to do the following string replacement so that 'cargo fetch'
     # doesn't ignore the versions specified in Cargo.lock
-set +u
     substituteInPlace Cargo.lock \
         --replace "registry+https://github.com/rust-lang/crates.io-index" \
                   "registry+file://$rustRegistry"
-set -u
 
     # Do any possible 'cargo update -p <pkgName> --precise <version>' ad-hoc updates
     eval "$cargoUpdateHook"
@@ -97,11 +92,9 @@ rm $out/config
     # We need to replace the rustRegistry URL with something deterministic.
     # Since the URL won't actually be accessed anymore, it's fine to use /dev/null.
 
-set +u
     substituteInPlace Cargo.lock \
         --replace "registry+file://$rustRegistry" \
                   "registry+file:///dev/null"
-set -u
     mv Cargo.lock $out/
 
 
@@ -181,3 +174,4 @@ done)
     # sporadic hash mismatches
     find $out ! -type f
     find $out -type f -exec sha256sum {} +
+}

pkgs/build-support/rust/fetchcargo.nix

@@ -9,8 +9,11 @@ stdenv.mkDerivation {
   phases = "unpackPhase installPhase";
 
   installPhase = ''
+    source ${./fetch-cargo-deps}
+
     export SSL_CERT_FILE=${cacert}/etc/ssl/certs/ca-bundle.crt
-    bash ${./fetch-cargo-deps} . "$out"
+
+    fetchCargoDeps . "$out"
   '';
 
   outputHashAlgo = "sha256";