darwin.stdenv: drop libssh2 from the bootstrap

[reckenrode]

Description of changes

curlMinimal includes scp support, but Darwin doesn’t need it. Disabling it removes libssh2 as a bootstrap dependency, allowing it to be updated without forcing a full rebuild of Darwin.

Targeting staging due to rebuilds (this one last time).

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[reckenrode]

Prompted by the rebuilds due to #275641.

[vcunat]

Maybe curlMinimal should not support SCP by default? It certainly feels surprising to me.

[reckenrode]

Maybe curlMinimal should not support SCP by default? It certainly feels surprising to me.

Probably not for a few reasons:

1. Changing the default is technically a breaking change. This seems theoretical because it would require users to be using curlMinimal for its SCP support, but it’s possibly they may; hence technically a breaking change.
2. curl is defined as an override of curlMinimal. Changing the default for curlMinimal affects curl.

The latter in particular requires either duplicating the condition for enabling SCP in all-packages.nix, which is probably not the right approach, or redefining curlMinimal from curl instead of the other way around.

I tried the latter approach locally, but it results in an infinite recursion in the Darwin stdenv bootstrap because the bootstrap defines curl as super.curlMinimal. Fixing it requires duplicating the curlMinimal definition in the bootstrap.

Just changing the override in the Darwin stdenv bootstrap is the least invasive change to drop libssh2 from it. If Darwin is ever able to drop curl completely from the bootstrap, then it might be worth revisiting how curl is defined. For now, I’d prefer to keep the change localized to the bootstrap.

[vcunat]

Should be closed by PR #276762 on a quick glance.