Add a matrix of stdenvs to the flake

[thufschmitt]

For a (currently hardcoded and limited) list of stdenvs,
make .#$nix-${stdenvName} correspond to a Nix built with the
corresponding stdenv.

For example, .#nix-${clang11Stdenv} is Nix built with clang11.

Likewise, devShell.x86_64-linux.clang11StdenvPackages is a development shell for Nix with clang11

Fix #4129

/cc @Pamplemousse

[edolstra]

I don't think we should make devShell an attrset of derivations/shells. It's assumed to be a single derivation, like defaultPackage. So e.g. nix flake check won't check these. Maybe to enforce uniformity we should disallow attributes deeper than the expected level in the CLI...

Instead we probably should add a devShells flake output (and maybe rename devShell to defaultDevShell). That would also be less verbose since it can be searched by default, so instead of

nix develop .#devShell.x86_64-linux.clang11StdenvPackages

you could do

nix develop .#clang11StdenvPackages

[thufschmitt]

Oh indeed, devShells is much nicer. I’ve changed that in 6378f36, and I’ll probably open another PR shortly to make nix develop and the various nix flake commands aware of it

[Pamplemousse]

I tried to use nix develop .#clang11StdenvPackages with this PR, and I get an error:

nix --experimental-features "nix-command flakes" develop .#clang11StdenvPackages
warning: Git tree '/src/nix' is dirty
error: flake 'git+file:///src/nix?shallow=1' does not provide attribute 'devShells.x86_64-linuxclang11StdenvPackages', 'packages.x86_64-linux.clang11StdenvPackages', 'legacyPackages.x86_64-linux.clang11StdenvPackages' or 'clang11StdenvPackages'

nix --version
nix (Nix) 2.4pre20210805_d64f967

Also, completion gives other attributes:

.#defaultPackage     .#checks            .#                                                                               
.#hydraJobs          .#devShells         .#devShell                                                                       
.#nix-armv7l-linux   .#nix-armv6l-linux  .#nix                                                                            
.#nix-clang11Stdenv  .#nix-clangStdenv   .#nix-gccStdenv                                                                  
.#nix-stdenv         .#nix-static        .#overlay

It should be nix develop .#nix-clang11Stdenv .

[Ericson2314]

I do like this. I will build on this to duplicate the cross / static stuff.

(It was only ever the is only the way it use because there used to be an issue with nix being overridden in https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/static.nix, but it no longer is overridden there.)

[edolstra]

This should be .#clang11StdenvPackages now right?

[thufschmitt]

Indeed, thanks. And actually the flake search path was broken (was missing a trailing .), so I fixed it.

I’ve also fixed the command above to use devShells and not devShell

[Pamplemousse]

Also, it seems that the devShell 's shellHook (https://github.com/NixOS/nix/blob/master/flake.nix#L614-L619) is ran OK when doing nix develop, but not when doing nix develop .#nix-clang11Stdenv .

Example:

$ nix develop .#nix-clang11Stdenv
warning: Git tree '/home/pamplemousse/Workspace/tools/nix' is dirty
$ echo $MANPATH

$ nix develop                    
warning: Git tree '/home/pamplemousse/Workspace/tools/nix' is dirty
$ echo $MANPATH
/home/pamplemousse/Workspace/tools/nix/outputs/out/share/man:

[Pamplemousse]

Ah, nevermind!
I got confused because nix develop .#clang11StdenvPackages did not work (because of the missing .), so I started using .#nix-clang11Stdenv, which does NOT use devShells)...

Now, I use nix develop .#.clang11StdenvPackages (notice the extra dot), and the shellHook gets called properly.

[Pamplemousse]

This is blocking for google/oss-fuzz#6317, as they require good upstream integration (they won't merge as long as I use my fork of nix over there).

Is there anything blocking the merge?

[Ericson2314]

Can we get this in before 2.4? I think it is decently important, and I would like to delete the duplicate mkDerivation for static and cross nix too.

[Ericson2314]

We would make something like forAllSystemsAndCrossSystemsAndStdenvs. https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/release-lib.nix has some stuff which might be useful to look at.

[thufschmitt]

Rebased on top of latest master.

@edolstra care to have a look?

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/tweag-nix-dev-update-23/16631/1