stdenv.mkDerivation: fix unpackPhase for archives with bad permissions

[milahu]

this fails in unpackPhase, because the lib/ folder in https://registry.npmjs.org/pngjs/-/pngjs-6.0.0.tgz has mode 0444, but should have mode 0555

when the executable flag is missing on a directory, its contents cannot be listed, which gives the Cannot open: Permission denied errors

nix-build -E '
  with import <nixpkgs> { };
  stdenv.mkDerivation {
    name = "x";
    src = fetchurl {
      url = "https://registry.npmjs.org/pngjs/-/pngjs-6.0.0.tgz";
      hash = "sha512-TRzzuFRRmEoSW/p1KVAmiOgPco2Irlah+bGFCeNfJXxxYGwSw7YwAOAcd7X28K/m5bjBWKsC29KyoMfHbypayg==";
    };
    buildPhase = "ls -l $src; exit 1";
  }'

this derivation will be built:
  /nix/store/5nvbj071zy4bdxx73gw5f6dlhxcb8fw3-x.drv
building '/nix/store/5nvbj071zy4bdxx73gw5f6dlhxcb8fw3-x.drv'...
unpacking sources
unpacking source archive /nix/store/jb1wi55v5z2gzx2rjma0v5323fij6wjp-pngjs-6.0.0.tgz
tar: package/lib/bitmapper.js: Cannot open: Permission denied
tar: package/lib/bitpacker.js: Cannot open: Permission denied
tar: package/lib/chunkstream.js: Cannot open: Permission denied
tar: package/lib/constants.js: Cannot open: Permission denied
tar: package/lib/crc.js: Cannot open: Permission denied
tar: package/lib/filter-pack.js: Cannot open: Permission denied
tar: package/lib/filter-parse-async.js: Cannot open: Permission denied
tar: package/lib/filter-parse-sync.js: Cannot open: Permission denied
tar: package/lib/filter-parse.js: Cannot open: Permission denied
tar: package/lib/format-normaliser.js: Cannot open: Permission denied
tar: package/lib/interlace.js: Cannot open: Permission denied
tar: package/lib/packer-async.js: Cannot open: Permission denied
tar: package/lib/packer-sync.js: Cannot open: Permission denied
tar: package/lib/packer.js: Cannot open: Permission denied
tar: package/lib/paeth-predictor.js: Cannot open: Permission denied
tar: package/lib/parser-async.js: Cannot open: Permission denied
tar: package/lib/parser-sync.js: Cannot open: Permission denied
tar: package/lib/parser.js: Cannot open: Permission denied
tar: package/lib/png-sync.js: Cannot open: Permission denied
tar: package/lib/png.js: Cannot open: Permission denied
tar: package/lib/sync-inflate.js: Cannot open: Permission denied
tar: package/lib/sync-reader.js: Cannot open: Permission denied
tar: Exiting with failure status due to previous errors
do not know how to unpack source archive /nix/store/jb1wi55v5z2gzx2rjma0v5323fij6wjp-pngjs-6.0.0.tgz
error: builder for '/nix/store/5nvbj071zy4bdxx73gw5f6dlhxcb8fw3-x.drv' failed with exit code 1;

why

cd $(mktemp -d)

wget https://registry.npmjs.org/pngjs/-/pngjs-6.0.0.tgz

tar xf *.tgz --warning=no-timestamp --warning=no-unknown-keyword --no-same-owner --no-same-permissions --delay-directory-restore

stat -c%a package/
# 644

chmod -R +wX package/

stat -c%a package/
# 755

fix

1. add more arguments to tar xf "$fn" --warning=no-timestamp

for example tar xf "$fn" --warning=no-timestamp --warning=no-unknown-keyword --no-same-owner --no-same-permissions --delay-directory-restore

2. after tar xf run chmod -R +X "${sourceRoot}" to add the executable flag on all directories. this can be merged with chmod -R +w "${sourceRoot}" to chmod -R +wX "${sourceRoot}"