#187 (comment)

Parsing type strings is hacky and we can do better for all types. For this issue, we will update lib.nix to extract the type, and update types.py to handle type checking without parsing.

Simple case

nix-instantiate --eval '<nixpkgs/nixos>' --arg configuration '{}' -A "options.sound.enable.type.name"
"bool"

A complex YAML type example

NixOS/nixpkgs#99132

The above PRs author suggests we can break down each component of a type so it's more specific than YAML (AnythingType):

nix-instantiate --eval '<nixpkgs/nixos>' --arg configuration '{}' -A "options.services.zrepl.settings.type.nestedTypes.freeformType.nestedTypes.elemType.nestedTypes.left.nestedTypes.left.nestedTypes.left.nestedTypes.left.nestedTypes.left.name"
"bool"

Submodules

Get submodule structure in cases where <name> and * don't exist

Some options, for example system.userActivationScripts, system.activationScripts, services.certmgr.specs, programs.firejail.wrappedBinaries have the types AttrsOf(Submodule) or ListOf(Submodule), however there isn't system.userActivationScripts."<name>".options in the option tree.

Additionally, some options are simply submodules whose structure isn't discoverable through the option tree.

pkgs.nixosOptionsDoc is insufficient to get data about all submodules, however matrix user sternenseemann has suggested:

(builtins.head ((nixos {}).options.system.userActivationScripts.type.nestedTypes.elemType.nestedTypes.right.getSubModules)) which gives us details about the structure of submodules.

Types with Checks

Types that have checks (e.g. time.timezone is "null or string without spaces"):

nix-instantiate --eval '<nixpkgs/nixos>' --arg configuration '{}' -A "options.time.timeZone.type.name"
"nullOr"

nix-instantiate --eval '<nixpkgs/nixos>' --arg configuration '{}' -A "options.time.timeZone.type.nestedTypes.elemType.name"
"str"

nix-instantiate --eval '<nixpkgs/nixos>' --arg configuration '{}' -A "options.time.timeZone.type.nestedTypes.elemType.check"
<LAMBDA>

# We can execute the typecheck as follows
nix-instantiate --eval -E 'let nixos = (import <nixpkgs/nixos> {configuration={};}); in nixos.options.time.timeZone.type.nestedTypes.elemType.check "foo"'
true

nix-instantiate --eval -E 'let nixos = (import <nixpkgs/nixos> {configuration={};}); in nixos.options.time.timeZone.type.nestedTypes.elemType.check "foo bar"'
false