Hi Guix, Nix flake has a convenient URL-like syntax to represent flake references and I wonder if something similar can be implemented in Guix. I think one approach is to transform .guix-channel into a channels.scm, and to do so will require more information to be included in .guix-channel. In this mail I'll explain why.
Here's an example of Nix flake's syntax[1]: you can build and run PatchELF from the development repository: --8<---------------cut here---------------start------------->8--- nix shell git+https://github.com/NixOS/patchelf#patchelf --command patchelf --help nix shell git+https://github.com/NixOS/patchelf?ref=master&rev=3e996dbef1fa0658012f8dd290bddcf0302acade#patchelf --command patchelf --help --8<---------------cut here---------------end--------------->8--- This works because PatchELF provides a flake.nix[2] in its repository root to specify its inputs and outputs, and what we get is the outputs: --8<---------------cut here---------------start------------->8--- { description = "A tool for modifying ELF executables and libraries"; inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable"; # dev tooling inputs.<...> outputs = <...> } --8<---------------cut here---------------end--------------->8--- PatchELF flake specifies Nixpkgs as its input, here ‘github:NixOS/nixpkgs/nixpkgs-unstable’ is similar to ‘git+https://github.com/NixOS/nixpkgs?ref=nixpkgs-unstable’, but is specialized and works more efficient for GitHub. Nixpkgs also provides a flake.nix in its repository root, which specifies outputs with no inputs (it doesn't depend on other flakes). So we can know how that syntax works: the repository specifies its dependencies (inputs and outputs) in a well-known location (flake.nix in repository root), so we can get enough information after knowing the repository content. In Guix we specify dependencies via a channels.scm and since recently we can fetch it from network: --8<---------------cut here---------------start------------->8--- guix time-machine -C https://ci.guix.gnu.org/eval/latest/channels.scm?spec=master -- shell patchelf -- patchelf --help --8<---------------cut here---------------end--------------->8--- Additionally, channels can specify their inputs (‘dependencies’, with the main Guix channel implicitly) and outputs (‘news-file’, ‘directory’) in a metadata file named ‘.guix-channel’[3], in the repository root. Yes, in the repository root, .guix-channel in the repository root, a well-known location! So we actually have met the minimum requirements, we can specify dependencies and we have a well-known location. What's left is to implement it. The natural approach I can think of is to use the existing interfaces and transform .guix-channel into channels.scm, so we can do something like --8<---------------cut here---------------start------------->8--- guix time-machine -C git+https://example.com/channel -- shell patchelf -- patchelf --help --8<---------------cut here---------------end--------------->8--- Then I realized that .guix-channel doesn't contain enough information for the channel itself. Consider the following channels.scm, with all available fields filled in for demonstration: --8<---------------cut here---------------start------------->8--- (list (channel (name 'guix) (url "https://git.guix.gnu.org/guix.git";) (branch "master") (commit "02c5f415db656148afa498bae8aa5a6c8b15c615") (introduction (make-channel-introduction "9edb3f66fd807b096b48283debdcddccfea34bad" (openpgp-fingerprint "BBB0 2DDF 2CEA F6A8 0D1D E643 A2A0 6DF2 A33A 54FA")))) (channel (name 'example) (url "https://example.com/channel";) (branch "trunk") (commit "5ca733f083ec59ea01964f02540655d8c533319b") (introduction (make-channel-introduction "3eca3dd8bf4c1d65f5c5a43c00ee5299b9580b6e" (openpgp-fingerprint "B472 C7FB D834 1922 60EB 3039 E09C D764 A177 711D"))))) --8<---------------cut here---------------end--------------->8--- Then the example channel would have the following .guix-channel, with all available fields filled in for demonstration: --8<---------------cut here---------------start------------->8--- (channel (version 0) (url "https://example.com/channel";) (keyring-reference "keyring") (news-file "NEWS") (directory "modules") (dependencies (channel (name guix) (url "https://git.guix.gnu.org/guix.git";) (branch "master") (commit "02c5f415db656148afa498bae8aa5a6c8b15c615") (introduction (channel-introduction (version 0) (commit "a8883b58dc82e167c96506cf05095f37c2c2c6cd") (signer "CABB A931 C0FF EEC6 900D 0CFB 090B 1199 3D9A EBB5")))))) --8<---------------cut here---------------end--------------->8--- branch, commit, and introduction are missing for the channel itself. So information in .guix-channel alone is insufficient to construct the equivalent channels.scm. As a result, I consider it's useful to add more information into .guix-channel. It can be a prerequisite for the convenient URL-like syntax, and ability to construct a channels.scm from .guix-channel may enable more tooling as well. WDYT? Thanks [1]: https://nix.dev/manual/nix/2.34/command-ref/new-cli/nix3-flake#flake-references [2]: https://github.com/NixOS/patchelf/blob/master/flake.nix [3]: https://guix.gnu.org/manual/1.5.0/en/html_node/Package-Modules-in-a-Sub_002ddirectory.html https://guix.gnu.org/manual/1.5.0/en/html_node/Declaring-Channel-Dependencies.html https://guix.gnu.org/manual/1.5.0/en/html_node/Specifying-Channel-Authorizations.html https://guix.gnu.org/manual/1.5.0/en/html_node/Primary-URL.html https://guix.gnu.org/manual/1.5.0/en/html_node/Writing-Channel-News.html
