We're calling `wait4path` on the full, resolved `@bindir@/nix-daemon` path.

That means we're hardcoding something like:

    /bin/wait4path /nix/store/zs9c5xhp3zv9p23qnjxp87nl5injsi1i-nix-2.3/bin/nix-daemon && /nix/var/nix/profiles/default/bin/nix-daemon

That seems unnecessarily fragile.

It might be better to wait4path on the path we intend to call.

On Catalina, the /nix filesystem might not be mounted at start time.
To avoid this service not starting, we need to keep the launch agent
outside of the Nix store. A wait4pid will hold for our /nix dir to be
mounted.

Fixes #3125.

launchd has some weird syntx. Apparently the program needs to be in
the ProgramArguments, as Program appears to be ignored.

When using a volume, the nix-daemon path may not exist. To avoid this
issue, we must use the wait4path tool. This should solve one of the
issues in multi-user on macOS Catalina.

Signed-off-by: Piotr Szubiakowski <pszubiak@eso.org>

Since macOS 10.14 this has become an error, causing problems if the
nix-daemon loads nix during substitution (this is a forked process).

Workaround for #2523.

We have automated builds at https://hub.docker.com/r/nixos/nix/ now. The master
branch of the "docker" repository is available as "latest". Branches that match
the regular expression "^[0-9.]+$" are pushed to the tag that corresponds to
their branch name. Other branches are ignored.

Without this the daemon won't be restarted if the process ever dies, for
example when sending a SIGHUP to reload nix.conf.

The path /root/.nix-profile is a sym-link to /nix/var/nix/profiles/default. The
latter path, however, works for everyone while the former path works only for
root, so we prefer the public path whenever possible.

- Use the latest Nix version 1.11.14.

- Attempts to download the Nix installation tarball from http://nixos.org
  redirect to https these days, which wget doesn't support unless OpenSSL is
  available.

- Use addgroup and adduser commands to create the Nix build users.

- Link the Nix profile script into /etc/profile.d, where it's run
  automatically.

- Dropped installation of bash and tar. Neither tool is essential for running
  Nix.

Use the command "docker build -t nix . && docker run -it --rm nix sh -"
to build and run the Nix docker container.

This removes the file nix-mode.el from Nix. The file is now available within the
repository https://github.com/NixOS/nix-mode.

Fixes #662
Fixes #1040
Fixes #1054
Fixes #1055
Closes #1119
Fixes #1419

NOTE: all of the above should be fixed within NixOS/nix-mode. If one of those
hasn’t please reopen within NixOS/nix-mode and not within NixOS/nix.

This is mostly to ensure that when Nix is started on macOS via a
launchd service or sshd (for a remote build), it gets a certificate
bundle.

Otherwise starting nix-daemon fails

● nix-daemon.service - Nix Daemon
   Loaded: loaded
(/nix/store/mnf00a6gc55xl47smk0b32gmi7xpvlfp-nix-1.12pre5308_2f21d522/lib/systemd/system/nix-daemon.service;
enabled; vendor preset: enabled)
  Drop-In:
/nix/store/m2rgjp71n4kyp8j5fxgbrlv13scd5vvv-system-units/nix-daemon.service.d
           └─overrides.conf
   Active: failed (Result: exit-code) since Sat 2017-04-29 11:29:21
CEST; 9s ago
  Process: 7299 ExecStart=nix-daemon --daemon (code=exited, status=1/FAILURE)
 Main PID: 7299 (code=exited, status=1/FAILURE)
      CPU: 19ms

... systemd[1]: Started Nix Daemon.
... nix-daemon[7299]: error: $XDG_CONFIG_HOME and $HOME are not set
... systemd[1]: nix-daemon.service: Main process exited, code=exited, status=1/FAILURE
... systemd[1]: nix-daemon.service: Unit entered failed state.
... systemd[1]: nix-daemon.service: Failed with result 'exit-code'.
... systemd[1]: nix-daemon.service: Start request repeated too quickly.
... systemd[1]: Failed to start Nix Daemon.
... systemd[1]: nix-daemon.service: Failed with result 'exit-code'.

This prevents collisions with the "native" OpenSSL, in particular on
OS X.

Fixes #921.

Nix requires either $HOME or $XDG_CACHE_HOME to be set.

Otherwise in particular https://cache.nixos.org won't work in the
daemon.

* Dockerfile: add GNU tar native dependency

`builtins.fetchTarball` requires GNU tar to be available in the $PATH in
order to unpack the fetched tarball (there is a FIXME comment for this),
which Alpine does not ship by default (it ships BusyBox tar).

* Dockerfile: add GNU bash native dependency

`nix-shell` defaults to invoking `bash` from the $PATH for the subshell.
In theory this can be overriden with the NIX_BUILD_SHELL environment
variable, but this does not work properly. `nix-shell` generates and
passes a script (`$rcFile`) to be executed by the subshell which uses
bashisms (`source` and `shopt`). Additionally, in interactive mode,
`nix-shell` passes the `--rcfile` argument to the shell, which is
another bashism.

Because `bash` is thus de-facto required, add `bash` as a native package
dependency to make it available for `nix-shell`.

If keywords are matched on the start/end of words then
keywords are also matched if they are surrounded by dashes
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