Don't auto-`callPackage`

[roberth]

The current proposal is rather restrictive when it comes to what's in the files.

We already established that callPackage has a number of issues, among which the need for default arguments to live outside the package function, and the package being defined through a function rather than a fixed point in the first place.
By doing a figurative mapAttrs callPackage we knowingly paint ourselves into a corner.

[xaverdh]

well, we can still add a second fresh directory with different semantics when a decision is made to move away from callPackage?

[roberth]

From what I understand, moving files en masse leads to many merge conflicts in PRs.
When moving the file, doing a s/.*/pkgs: pkgs.callPackage (\0) { }/ seems to be worth considering. It also lets us cover packages with non-default arguments.

[roberth]

By using package.nix as the file name for auto called packages, we have more freedom to reuse the same directory structure while migrating to a more declarative (functions are a problem) non-callPackage overriding solution. We might want to reserve package.nix for the final declarative format though.