fix(flake-info): tighten home-manager flake detection (#1235)

Detecting home-manager flakes by `modules/modules.nix` alone produced
false positives for unrelated flakes that happen to ship a similarly
named file (e.g. `nix-bitcoin`). Once a non-HM flake matched, the
subsequent `import` of `modules/lib/stdlib-extended.nix` aborted the
whole evaluation, so packages and options for those flakes also failed
to index.

Also require `modules/lib/stdlib-extended.nix` to be present, which is
specific to home-manager and is the helper `readHomeManagerOptions`
already imports.

Refs #1234

Author: KiaraGrouwstra

flake-info/assets/commands/flake_info.nix

@@ -518,9 +518,17 @@ rec {
   options = readFlakeOptions;
   home-manager-options =
     let
-      hasHmModules = builtins.tryEval (builtins.pathExists "${resolved}/modules/modules.nix");
+      # Require both `modules/modules.nix` and `modules/lib/stdlib-extended.nix`
+      # to avoid false positives. Other flakes (e.g. `nix-bitcoin`) ship a
+      # `modules/modules.nix` that is unrelated to home-manager; only
+      # home-manager itself also provides the `stdlib-extended.nix` helper
+      # that `readHomeManagerOptions` imports.
+      isHomeManager = builtins.tryEval (
+        builtins.pathExists "${resolved}/modules/modules.nix"
+        && builtins.pathExists "${resolved}/modules/lib/stdlib-extended.nix"
+      );
     in
-    if hasHmModules.success && hasHmModules.value then readHomeManagerOptions else [ ];
+    if isHomeManager.success && isHomeManager.value then readHomeManagerOptions else [ ];
   all = packages ++ apps ++ options ++ home-manager-options;
 
   nixos-options = builtins.filter (opt: !(isServiceOption opt)) nixpkgsAllOpts;