add default nix for dist builds

[thedavidmeister]

PR summary

Adds a default.nix file that includes only the binaries.

Facilitates pointing nix-env straight at a tarball if all you want is the binaries.

Ignores all of the dependencies!

I'm chasing up a vanity URL from @duffybelfield

The "easy install" for binaries would look like this:

# install nix tooling on mac/linux
curl https://nixos.org/nix/install | sh

# drop holochain and hc binaries into the user's path
nix-env -f https://holochain.love -iA hc holochain

How does this work?

1. the nix installer 1-liner creates nix-shell and nix-env (and others) on mac/linux
2. pointing nix-env at a URL will look for a tarball, unpack it and look for default.nix
3. https://holochain.love (will) points to https://github.com/holochain/holochain-rust/archive/master.tar.gz
4. the default.nix (added in this PR) exposes the hc and holochain binary derivations from holonix
5. the -i flag tells nix-env to "install"
6. the -A flag tells nix-env the names of the derivations to be installed
7. nix-env copies the output of the hc and holochain derivations into the user's home directory (just the binaries)
8. hc and holochain end up in ~/.nix-profile/bin

and then later... to upgrade...

# upgrade derivations
nix-env -f https://holochain.love -uA hc holochain

at least i think this works 🤔

i guess we will find out!!!

finally, to uninstall...

# uninstall binaries
nix-env -e hc holochain

to track develop rather than master we have https://holochain.love/nightly as well

testing/benchmarking notes

Example of a round trip (installing and uninstalling):

Currently https://bit.ly/2DG8SW9 points to https://github.com/holochain/holochain-rust/archive/675685ae62392805d95da0a961d8a1d5d32a80de.tar.gz

[thedavidmeister@nixos:~]$ hc -V
hc: command not found

[thedavidmeister@nixos:~]$ holochain -V
holochain: command not found

[thedavidmeister@nixos:~]$ nix-env -f https://bit.ly/2DG8SW9 -iA hc holochain
installing 'hc'
installing 'holochain'

[thedavidmeister@nixos:~]$ hc -V
hc 0.0.13-alpha1

[thedavidmeister@nixos:~]$ holochain -V
holochain 0.0.13-alpha1

[thedavidmeister@nixos:~]$ which hc
/home/thedavidmeister/.nix-profile/bin/hc

[thedavidmeister@nixos:~]$ which holochain
/home/thedavidmeister/.nix-profile/bin/holochain

[thedavidmeister@nixos:~]$ nix-env -f https://bit.ly/2DG8SW9 -e hc holochain
uninstalling 'hc'
uninstalling 'holochain'

[thedavidmeister@nixos:~]$ hc -V
hc: command not found

[thedavidmeister@nixos:~]$ holochain -V
holochain: command not found

[thedavidmeister@nixos:~]$ 

( if any manual testing or benchmarking was/should be done, add notes and/or screenshots here )

followups

( any new tickets/concerns that were discovered or created during this work but aren't in scope for review here )

changelog

Please check one of the following, relating to the CHANGELOG

• this is a code change that effects some consumer (e.g. zome developers) of holochain core so there is an 'Unreleased' CHANGELOG item, with the format - summary of change [PR#1234](https://github.com/holochain/holochain-rust/pull/1234)
• this is not a code change, or doesn't effect anyone outside holochain core development

[dhtnetwork]

Reviewed/Passed with flying colors! Green all the way.
Successful install and uninstall.

[dhtnetwork]

Followed the steps outlined:

1. Read the instructions.
2. Steps completed

install nix tooling on mac/linux

• curl https://nixos.org/nix/install | sh
• Added To ensure that the necessary environment
  variables are set, please add the line
  . /Users/signal/.nix-profile/etc/profile.d/nix.sh
• nix-env -f https://bit.ly/2DG8SW9 -iA hc holochain
• completed the install and uninstall process twice.

[pdaoust]

Would be good to follow this up with updates to the Quick Start Guide, providing examples for both nix-env and nix-shell and explaining why you would want one or the other.

[philipbeadle]

love using nix