nixos-rebuild-ng: disable flake auto-detection when --file or --attr is used (#527046)

pkgs/by-name/ni/nixos-rebuild-ng/nixos-rebuild.8.scd

@@ -314,13 +314,16 @@ It must be one of the following:
 	be made using _nixos_ function in nixpkgs or importing and calling
 	nixos/lib/eval-config.nix from nixpkgs. If specified without *--attr*
 	option, builds the configuration from the top-level attribute set of the
-	file.
+	file. Using this option disables automatic flake detection, same as
+	*--no-flake*.
 
 *--attr* _attrPath_, *-A* _attrPath_
 	Build the NixOS system from a nix file and use the specified
 	attribute path from the file specified by the *--file* option.
 	If specified without *--file* option, uses _system.nix_ in current directory,
 	the system-wide _<nixos-system>_ file, or finally, /etc/nixos/system.nix.
+	Using this option disables automatic flake detection, same as
+	*--no-flake*.
 
 *--flake* _flake-uri[#name]_, *-F* _flake-uri[#name]_
 	Build the NixOS system from the specified flake. It defaults to the

pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/__init__.py

@@ -329,6 +329,10 @@ def parse_args(
     if args.flake and (args.file or args.attr):
         parser.error("--flake cannot be used with --file or --attr")
 
+    if (args.file or args.attr) and args.flake is None:
+        # Disable flake auto-detection when --file or --attr is used
+        args.flake = False
+
     if args.store_path:
         if args.rollback:
             parser.error("--store-path and --rollback are mutually exclusive")

pkgs/by-name/ni/nixos-rebuild-ng/src/tests/test_main.py

@@ -89,6 +89,22 @@ def test_parse_args() -> None:
     assert r_store_path.flake is False
     assert r_store_path.store_path == "/nix/store/foo"
 
+    # --file and --attr should disable flake auto-detection
+    r_file, _ = nr.parse_args(["nixos-rebuild", "switch", "--file", "foo.nix"])
+    assert r_file.flake is False
+    assert r_file.file == "foo.nix"
+
+    r_attr, _ = nr.parse_args(["nixos-rebuild", "switch", "--attr", "bar"])
+    assert r_attr.flake is False
+    assert r_attr.attr == "bar"
+
+    r_file_attr, _ = nr.parse_args(
+        ["nixos-rebuild", "switch", "--file", "foo.nix", "--attr", "bar"]
+    )
+    assert r_file_attr.flake is False
+    assert r_file_attr.file == "foo.nix"
+    assert r_file_attr.attr == "bar"
+
     r1, g1 = nr.parse_args(
         [
             "nixos-rebuild",