Cross-posting https://matrix.to/#/!wfudwzqQUiJYJnqfSY:nixos.org/$VKmzIvXR8HqZgjBta5cdud9hjyKoXNAvilyvwZbd5nE?via=nixos.org&via=matrix.org&via=nixos.dev (message from the NixOS Module System room) because I'm very confused and I don't seem to be getting enough eyeballs in that room 🙂

TL;DR: overriding an option-type using ty // { merge = someOtherFn; } seems to be inconsistently broken and I can't figure out what's going on...

In reply to @tazjin:matrix.org
Matt Sturgeon: I think "inconsistently broken" needs to be expanded on a bit if you want people to be able to help ;)

I'll try and summarize here:

This PR is moving some logic from the various option's apply functions into the type's merge function.

This is done using the type // { merge = /* ... */; } pattern.

Everything works fine when using the produced type in a repl, but in practice the overridden merge function is not used (the original type's merge function is instead).

This can be observed in CI failures complaining that "the option lua is accessed but not defined". When the merge function is correctly overridden, lua will not be accessed.

I tried to make an MRE, however it is unable to reproduce the issue.

In particular, nixvimConfiguration._module.specialArgs.lib.nixvim.keymaps.deprecatedMapOptionSubmodule works fine, but nixvimConfiguration.options.keymaps.type.nestedTypes.elemType does not. Bizzarely, these two should be the same type; the latter comes from:

keymaps = lib.mkOption {
  type = lib.types.listOf lib.nixvim.keymaps.deprecatedMapOptionSubmodule;
  # ...
}

I'll try and summarize here:

This PR is moving some logic from the various option's apply functions into the type's merge function.

This is done using the type // { merge = /* ... */; } pattern.

Everything works fine when using the produced type in a repl, but in practice the overridden merge function is not used (the original type's merge function is instead).

This can be observed in CI failures complaining that "the option lua is accessed but not defined". When the merge function is correctly overridden, lua will not be accessed.

I tried to make an MRE, however it is unable to reproduce the issue. Hence why I'm still talking about the PR where I actually see the issue. I also had this issue a wile back in an unrelated PR.

In particular, nixvimConfiguration._module.specialArgs.lib.nixvim.keymaps.deprecatedMapOptionSubmodule works fine, but nixvimConfiguration.options.keymaps.type.nestedTypes.elemType does not. Bizzarely, these two should be the same type; the latter comes from:

keymaps = lib.mkOption {
  type = lib.types.listOf lib.nixvim.keymaps.deprecatedMapOptionSubmodule;
  # ...
}

I'll try and summarize here:

This PR is moving some logic from the various option's apply functions into the type's merge function.

This is done using the type // { merge = /* ... */; } pattern.

Everything works fine when using the produced type in a repl, but in practice the overridden merge function is not used (the original type's merge function is instead).

This can be observed in CI failures complaining that "the option lua is accessed but not defined". When the merge function is correctly overridden, lua will not be accessed.

I tried to make an MRE, however it is unable to reproduce the issue. Hence why I'm still talking about the PR where I actually see the issue. I also had this issue a wile back in an unrelated PR.

In particular, nixvimConfiguration._module.specialArgs.lib.nixvim.keymaps.deprecatedMapOptionSubmodule works fine, but nixvimConfiguration.options.keymaps.type.nestedTypes.elemType does not. Bizzarely, these two should be the same type; the latter comes from:

keymaps = lib.mkOption {
  type = lib.types.listOf lib.nixvim.keymaps.deprecatedMapOptionSubmodule;
  # ...
}

As seen in my MRE, just using evalModules or listOf is not enough to reproduce the issue. Something else weird is going on.