Allow selecting derivation outputs

[edolstra]

This allows selecting the outputs of a derivation nix should operate on using the syntax installable^outputs, e.g. nixpkgs#glibc^dev,static or nixpkgs#glibc^*. By default, nix will use the outputs specified by the derivation's meta.outputsToInstall attribute if it exists, or all outputs otherwise.

Depends on #6426.

[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-29/18903/1

[edolstra]

I've changed the ! character to ^ to make it easier on shell users.

[dpulls]

🎉 All dependencies have been resolved !

[Ericson2314]

@edolstra you still did not address and instead many of the issues in the other thread, once again.

• nixpkgs#glibc.dev not working is terrible UI

• Syntax is subtly inconsistent/ambiguous given accepted RFC 92

[nixos-discourse]

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

https://discourse.nixos.org/t/recent-nix-change-worthy-of-greater-attention/18972/1

[roberth]

It would be useful for this to operate at the expression level, rather than the store level, so that packages can be split across derivations. Here's a use case where it breaks NixOS/nixpkgs#175785 (comment)

Another use case is for packages that use heavy tooling in their docs output. Splitting those docs out into a separate derivation reduces the build closure size.

See also #6507