Don't check NixOS modules

NixOS modules can be paths. Rather than dig further down into the layer
violation, don't check anything specific to NixOS modules.

src/nix/flake.cc

@@ -381,23 +381,6 @@ struct CmdFlakeCheck : FlakeCommand
         auto checkModule = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
                 state->forceValue(v, pos);
-                if (v.isLambda()) {
-                    if (!v.lambda.fun->hasFormals() || !v.lambda.fun->formals->ellipsis)
-                        throw Error("module must match an open attribute set ('{ config, ... }')");
-                } else if (v.type() == nAttrs) {
-                    for (auto & attr : *v.attrs)
-                        try {
-                            state->forceValue(*attr.value, attr.pos);
-                        } catch (Error & e) {
-                            e.addTrace(
-                                state->positions[attr.pos],
-                                hintfmt("while evaluating the option '%s'", state->symbols[attr.name]));
-                            throw;
-                        }
-                } else
-                    throw Error("module must be a function or an attribute set");
-                // FIXME: if we have a 'nixpkgs' input, use it to
-                // check the module.
             } catch (Error & e) {
                 e.addTrace(resolve(pos), hintfmt("while checking the NixOS module '%s'", attrPath));
                 reportError(e);

tests/flakes/check.sh

@@ -41,9 +41,9 @@ nix flake check $flakeDir
 cat > $flakeDir/flake.nix <<EOF
 {
   outputs = { self }: {
-    nixosModules.foo = {
+    nixosModules.foo = assert false; {
       a.b.c = 123;
-      foo = assert false; true;
+      foo = true;
     };
   };
 }
@@ -63,18 +63,6 @@ EOF
 
 nix flake check $flakeDir
 
-cat > $flakeDir/flake.nix <<EOF
-{
-  outputs = { self }: {
-    nixosModule = { config, pkgs }: {
-      a.b.c = 123;
-    };
-  };
-}
-EOF
-
-(! nix flake check $flakeDir)
-
 cat > $flakeDir/flake.nix <<EOF
 {
   outputs = { self }: {