Add #flakeModules.flakeModulesSansAlias

[mightyiam]

Importing flakeModules.flakeModules
results in an always-failing nix flake check.

This seems to be because it adds a value to
flake.flakeModules.flakeModule that ends up as a flake output that
fails to evaluate with the error:

Renaming error: option `flakeModules.default' does not exist.

[roberth]

That would be caused by

flake-parts/extras/flakeModules.nix

Line 39 in c621e84

(mkAliasOptionModule [ "flakeModule" ] [ "flakeModules" "default" ])

To solve this problem, we'd have to either make that behavior optional, or remove it entirely.
By making it optional in an automatic way, we'll introduce an infinite recursion when accessing self.outPath (or self itself, any attr) from within a flakeModules definition, breaking directory-based autodiscovery solutions.
By removing it, we cause trouble for users who import flakeModule, as it will disappear without an error message that tells them what to do.

The only solution is see is to add an option like enableFlakeModuleAlias so that you can disable that attr in your flake.
Or split the module into a new one that declares flakeModules and another that imports the new one and adds the alias. Then you can import the new module without the alias.

[mightyiam]

Split module sounds 🏆 to me.

[mightyiam]

Could use some help here:

$ nix flake check
error:
       … while checking flake output 'checks'

       … while checking the derivation 'checks.x86_64-linux.eval-tests'

       … while evaluating the attribute 'optionalValue.value'
         at /nix/store/80jiav8nl8hsx2sf4miaihfacajn1i5h-source/lib/modules.nix:974:5:
          973|
          974|     optionalValue =
             |     ^
          975|       if isDefined then { value = mergedValue; }

       … while evaluating definitions from `/nix/store/2g82mhkbp6cdnc33mag8cvmxxy8afcfr-source/extras/partitions.nix':

       … while evaluating definitions from `/nix/store/2g82mhkbp6cdnc33mag8cvmxxy8afcfr-source/modules/transposition.nix':

       … while evaluating definitions from `/nix/store/2g82mhkbp6cdnc33mag8cvmxxy8afcfr-source/dev/flake-module.nix, via option partitions.dev.module.perSystem':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: Module `/nix/store/2g82mhkbp6cdnc33mag8cvmxxy8afcfr-source/dev/tests/eval-tests.nix` contains a disabledModules item that is an attribute set, presumably a module, that does not have a `key` attribute. This means that the module system doesn't have any means to identify the module that should be disabled. Make sure that you've put the correct value in disabledModules: a string path relative to modulesPath, a path value, or an attribute set with a `key` attribute.

Which module is it that is missing a key and what is the change that causes this? I could grind against this some more but it's bed time.

[mightyiam]

flake.parts fails to build with this, claiming this input has no options to render.

[roberth]

Thank you for writing this.

Unfortunately I believe I've thought within the framework of the module system too much.
Dogfooding is still a UX issue, and I think it's worth solving monolithically in evalFlakeModule. A solution there would make this module obsolete.

I'm also leaning towards migrating to modules.flake.<name>, as modules.<class>.<name> is, in a larger context, a more flexible, cleaner place for such attributes.