buildFHSEnv: allow specifying executableName explicitly

[MattSturgeon]

Motivated by https://github.com/NixOS/nixpkgs/pull/369259/files#r1902238426, allows packages to specify a different exe name & pname.

Also simplified some logic with the name fallback, making it clearer what function args are available.

Tested with:

nix-build -A tests.buildFHSEnv

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/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 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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[S-K-Tiger]

I'm still learning the language but wouldn't the changes cause a error when either pname or version is not provided rather than only when missing both as the error message seems to indicate is intended?

  pname ? throw "You must provide either `name` or `pname`",
  version ? throw "You must provide either `name` or `version`",

[MattSturgeon]

I'm still learning the language but wouldn't the changes cause a error when either pname or version is not provided rather than only when missing both as the error message seems to indicate is intended?

  pname ? throw "You must provide either `name` or `pname`",
  version ? throw "You must provide either `name` or `version`",

If they are accessed directly, yes. However they are only accessed via name's fallback value, so they only get evaluated if name's fallback value is evaluated. I.e. if name isn't specified.

I'll add a note to make this explicit.

[MattSturgeon]

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 371770

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x86_64-linux

✅ 1 package built:

• nixpkgs-manual

[UlyssesZh]

This is also something I wanted to do. Thank you.