Patch the stdenv of nixpkgs with oils-for-unix and try to build something with it.

Requirements:

• nix
• ysh
• a clone of nixpkgs somewhere.

Usage

Prepare nixpkgs

# A certain commit needs to be checked out in nixpkgs for it to work:
cd nixpkgs
git checkout a481a7c16caae63e6b1dc2e20bebac20392c86c1
cd THIS-REPO
ln -s PATH-TO-NIXPKGS ./nixpkgs

Now you can test a build of bash:

# replace the oils tarball with the newest one from https://www.oilshell.org/. a `.tar` or `.tar.gz` should both work.
./nix-patched-build.ysh http://travis-ci.oilshell.org/github-jobs/6567/cpp-tarball.wwz/_release/oils-for-unix.tar

bind mount magic

To debug the stdenv it would be annoying to have to rebuild everytime we want to change e.g. the generated setup script. To make this process easier, there is the bind_mount_path.ysh file. It takes any path (usually /nix/store/xxx), copies this path to ./patch and bind-mounts it back to /nix/store. E.g.:

osh-0.20.0$ ./bind_mount_path.ysh /nix/store/3gfzhrywf5hriin0nbrkbr9c3hzqls84-bootstrap-stage0-stdenv-linux/
Destination ./patch/3gfzhrywf5hriin0nbrkbr9c3hzqls84-bootstrap-stage0-stdenv-linux doesn't exist. Copying
[sudo] password for samuelh:
mount: /home/samuelh/git/private/nixpkgs_oils_patch/patch/3gfzhrywf5hriin0nbrkbr9c3hzqls84-bootstrap-stage0-stdenv-linux bound on /nix/store/3gfzhrywf5hriin0nbrkbr9c3hzqls84-bootstrap-stage0-stdenv-linux.
osh-0.20.0$ ls -lah /nix/store/3gfzhrywf5hriin0nbrkbr9c3hzqls84-bootstrap-stage0-stdenv-linux/
total 52K
drwxr-xr-x 1 example users    32 Jan  1  1970 .
drwxrwxr-t 1 root    nixbld 8.6M Mar 31 16:00 ..
drwxr-xr-x 1 example users     0 Jan  1  1970 nix-support
-rw-r--r-- 1 example users   51K Jan  1  1970 setup
osh-0.20.0$ mount | grep /nix/stor
/dev/mapper/crypted on /nix/store type btrfs (ro,noatime,compress=zstd:3,ssd,discard=async,space_cache=v2,subvolid=257,subvol=/nix)
/dev/mapper/crypted on /nix/store/3gfzhrywf5hriin0nbrkbr9c3hzqls84-bootstrap-stage0-stdenv-linux type btrfs (rw,noatime,compress=zstd:3,ssd,discard=async,space_cache=v2,subvolid=256,subvol=/home)
osh-0.20.0$

As you see the setup file looks to be writable and owned by the example user. But in reality this is the file under ./patch/3gfzhrywf5hriin0nbrkbr9c3hzqls84-bootstrap-stage0-stdenv-linux/setup. (I'm sorry I have btrfs and cryptsetup. Otherwise the mount output would be more instructive :).