various: remove by-name overrides (part 4)

[mdaniels5757]

Split from #474456.

This is a step towards #454525, which will help enable checking for additional by-name directories (e.g. Python) in nixpkgs-vet.

Things done

• 0 rebuilds.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

[diniamo]

I'm not sure I undersrand. What is the point of this?

[paperdigits]

I do not get it either and I didn't find that trying to flow the other PRs provided me much clarity.

…

On January 25, 2026 9:56:37 PM PST, diniamo ***@***.***> wrote: diniamo left a comment (NixOS/nixpkgs#483859) I'm not sure I undersrand. What is the point of this? -- Reply to this email directly or view it on GitHub: #483859 (comment) You are receiving this because your review was requested. Message ID: ***@***.***>

[mdaniels5757]

I'm not sure I undersrand. What is the point of this?

Currently, packages defined in pkgs/by-name can be overridden, with the same name, in pkgs/top-level/all-packages.nix. So pkgs/by-name/fo/foo can have an all-packages.nix entry like:

  foo = callPackage ../by-name/fo/foo {
    bar = bar_2_0;
  };

This is problematic: both because it makes the package definition a bit harder to read (because it's not all in one place), and (more importantly IMO) it massively complicates checking the by-name directory in continuous integration. This is making it much much harder to, e.g., add a pkgs/development/python-modules/by-name directory, which would allow the merge bot to be used for those packages (which would be a huge win for maintainers (less waiting!) and committers (less work!)).

So we are moving to disallow overriding packages defined in by-name with the same name. This PR is a step towards removing the existing overrides.

[diniamo]

So in the case of Odin, llvmPackages is an override from all-packages? Or?

[mdaniels5757]

In pkgs/by-name/od/odin/package.nix before this PR's change, the value of the "llvmPackages" argument passed in is actually that of the package llvmPackages_18.

The thing we are trying to eliminate is everything of the form foo = callPackage ../by-name/fo/foo { ... } in all-packages.nix, for the reason above.

Note that e.g. foo_1_0 = ... is fine (as long as there is no package in by-name called foo_1_0). The problem is the override with the same name.

[diniamo]

Oh I missed the all-packages changes somehow. I get it now.

Looks good to me then.

[jopejoe1]

Thanks for doing this clean up.