feat: indirect inputs

default.nix

@@ -109,9 +109,11 @@ let
     name: sourceInfo: flake:
     let
       specs = flake.inputs or { };
-      names = builtins.attrNames specs;
       inputs = builtins.mapAttrs (sub: spec: resolveSubInput name sub spec) specs;
-      outputs = flake.outputs (inputs // { inherit self; });
+      indirect = builtins.mapAttrs (sub: _: resolveSubInput name sub { }) (
+        builtins.functionArgs flake.outputs
+      );
+      outputs = flake.outputs (indirect // inputs // { inherit self; });
       self =
         sourceInfo
         // outputs

fixtures/indirect-flake/flake.nix

@@ -0,0 +1,8 @@
+{
+  # Note: no inputs.nixpkgs declared — outputs takes `nixpkgs` indirectly.
+  outputs =
+    { nixpkgs, ... }:
+    {
+      usedNixpkgs = nixpkgs;
+    };
+}

tests.nix

@@ -225,6 +225,22 @@ in
     expected = "/nested-nixpkgs";
   };
 
+  # ── Indirect inputs (outputs function args not declared in inputs) ────────
+
+  indirect.test-outputs-accepts-indirect-input-override = {
+    # The flake at ./fixtures/indirect-flake has no inputs.nixpkgs declared,
+    # but its `outputs` takes a `nixpkgs` argument.
+    expr =
+      let
+        result = with-inputs {
+          nixpkgs = mkSrc "/our-nixpkgs";
+          mylib = mkSrc ./fixtures/indirect-flake;
+        } { };
+      in
+      result.mylib.usedNixpkgs.outPath;
+    expected = "/our-nixpkgs";
+  };
+
   # ── Functor / self ─────────────────────────────────────────────────────────
 
   functor-self.test-outputs-function-receives-with-inputsd-inputs = {