nixos-rebuild-ng: do not parse the path part from Flake as a Path

When I first wrote the Flake code for `nixos-rebuild-ng`, I set the
Flake parser to normalize the `foo` part from `foo#host` as a Python's
`pathlib.Path` if this looked like a path. The idea originally was to
improve type-safety and make it easier to compose the path later if
needed.

But, in retrospect this is the wrong thing to do here because there are
so many things that `nix` can do in those cases:
- `foo` can be either a directory or a Flake registry
- #433726

So let's stop being smart here and just assume a plain string. We don't
really get a lot of type-safety or any of the nice things pathlib gives
to us since there isn't any path manipulation going on. Let `nix` itself
handle any translation here.

Fix: #433726.

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

@@ -77,7 +77,7 @@ def _get_hostname(target_host: Remote | None) -> str | None:
 
 @dataclass(frozen=True)
 class Flake:
-    path: Path | str
+    path: str
     attr: str
     _re: ClassVar = re.compile(r"^(?P<path>[^\#]*)\#?(?P<attr>[^\#\"]*)$")
 
@@ -86,11 +86,7 @@ class Flake:
 
     @override
     def __str__(self) -> str:
-        if isinstance(self.path, Path):
-            # https://github.com/NixOS/nixpkgs/issues/433726
-            return f"{self.path.absolute()}#{self.attr}"
-        else:
-            return f"{self.path}#{self.attr}"
+        return f"{self.path}#{self.attr}"
 
     @classmethod
     def parse(cls, flake_str: str, target_host: Remote | None = None) -> Self:
@@ -101,10 +97,7 @@ class Flake:
             f'nixosConfigurations."{attr or _get_hostname(target_host) or "default"}"'
         )
         path = m.group("path")
-        if ":" in path:
-            return cls(path, nixos_attr)
-        else:
-            return cls(Path(path), nixos_attr)
+        return cls(path, nixos_attr)
 
     @classmethod
     def from_arg(cls, flake_arg: Any, target_host: Remote | None) -> Self | None:  # noqa: ANN401

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

@@ -33,10 +33,10 @@ def test_build_attr_to_attr() -> None:
 @patch("platform.node", autospec=True, return_value=None)
 def test_flake_parse(mock_node: Mock, tmpdir: Path, monkeypatch: MonkeyPatch) -> None:
     assert m.Flake.parse("/path/to/flake#attr") == m.Flake(
-        Path("/path/to/flake"), 'nixosConfigurations."attr"'
+        "/path/to/flake", 'nixosConfigurations."attr"'
     )
     assert m.Flake.parse("/path/ to /flake") == m.Flake(
-        Path("/path/ to /flake"), 'nixosConfigurations."default"'
+        "/path/ to /flake", 'nixosConfigurations."default"'
     )
     with patch(
         get_qualified_name(m.run_wrapper, m),
@@ -45,11 +45,11 @@ def test_flake_parse(mock_node: Mock, tmpdir: Path, monkeypatch: MonkeyPatch) ->
     ):
         target_host = m.Remote("target@remote", [], None)
         assert m.Flake.parse("/path/to/flake", target_host) == m.Flake(
-            Path("/path/to/flake"), 'nixosConfigurations."remote"'
+            "/path/to/flake", 'nixosConfigurations."remote"'
         )
-    assert m.Flake.parse(".#attr") == m.Flake(Path("."), 'nixosConfigurations."attr"')
-    assert m.Flake.parse("#attr") == m.Flake(Path("."), 'nixosConfigurations."attr"')
-    assert m.Flake.parse(".") == m.Flake(Path("."), 'nixosConfigurations."default"')
+    assert m.Flake.parse(".#attr") == m.Flake(".", 'nixosConfigurations."attr"')
+    assert m.Flake.parse("#attr") == m.Flake("", 'nixosConfigurations."attr"')
+    assert m.Flake.parse(".") == m.Flake(".", 'nixosConfigurations."default"')
     assert m.Flake.parse("path:/to/flake#attr") == m.Flake(
         "path:/to/flake", 'nixosConfigurations."attr"'
     )
@@ -64,7 +64,7 @@ def test_flake_parse(mock_node: Mock, tmpdir: Path, monkeypatch: MonkeyPatch) ->
 
 def test_flake_to_attr() -> None:
     assert (
-        m.Flake(Path("/path/to/flake"), "nixosConfigurations.preAttr").to_attr(
+        m.Flake("/path/to/flake", "nixosConfigurations.preAttr").to_attr(
             "attr1", "attr2"
         )
         == "/path/to/flake#nixosConfigurations.preAttr.attr1.attr2"
@@ -73,10 +73,9 @@ def test_flake_to_attr() -> None:
 
 def test_flake__str__(monkeypatch: MonkeyPatch, tmpdir: Path) -> None:
     assert str(m.Flake("github:nixos/nixpkgs", "attr")) == "github:nixos/nixpkgs#attr"
-    assert str(m.Flake(Path("/etc/nixos"), "attr")) == "/etc/nixos#attr"
-    with monkeypatch.context() as patch_context:
-        patch_context.chdir(tmpdir)
-        assert str(m.Flake(Path("."), "attr")) == f"{tmpdir}#attr"
+    assert str(m.Flake("/etc/nixos", "attr")) == "/etc/nixos#attr"
+    assert str(m.Flake(".", "attr")) == ".#attr"
+    assert str(m.Flake("", "attr")) == "#attr"
 
 
 @patch("platform.node", autospec=True)
@@ -87,7 +86,7 @@ def test_flake_from_arg(
 
     # Flake string
     assert m.Flake.from_arg("/path/to/flake#attr", None) == m.Flake(
-        Path("/path/to/flake"), 'nixosConfigurations."attr"'
+        "/path/to/flake", 'nixosConfigurations."attr"'
     )
 
     # False
@@ -97,7 +96,7 @@ def test_flake_from_arg(
     with monkeypatch.context() as patch_context:
         patch_context.chdir(tmpdir)
         assert m.Flake.from_arg(True, None) == m.Flake(
-            Path("."), 'nixosConfigurations."hostname"'
+            ".", 'nixosConfigurations."hostname"'
         )
 
     # None when we do not have /etc/nixos/flake.nix
@@ -122,7 +121,7 @@ def test_flake_from_arg(
         ),
     ):
         assert m.Flake.from_arg(None, None) == m.Flake(
-            Path("/etc/nixos"), 'nixosConfigurations."hostname"'
+            "/etc/nixos", 'nixosConfigurations."hostname"'
         )
 
     with (
@@ -138,7 +137,7 @@ def test_flake_from_arg(
         ),
     ):
         assert m.Flake.from_arg(None, None) == m.Flake(
-            Path("/path/to"), 'nixosConfigurations."hostname"'
+            "/path/to", 'nixosConfigurations."hostname"'
         )
 
     with (
@@ -149,7 +148,7 @@ def test_flake_from_arg(
         ),
     ):
         assert m.Flake.from_arg("/path/to", m.Remote("user@host", [], None)) == m.Flake(
-            Path("/path/to"), 'nixosConfigurations."remote-hostname"'
+            "/path/to", 'nixosConfigurations."remote-hostname"'
         )
 
 

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

@@ -385,7 +385,7 @@ def test_get_build_image_variants(mock_run: Mock, tmp_path: Path) -> None:
     ),
 )
 def test_get_build_image_variants_flake(mock_run: Mock) -> None:
-    flake = m.Flake(Path("/flake.nix"), "myAttr")
+    flake = m.Flake("/flake.nix", "myAttr")
     assert n.get_build_image_variants_flake(flake, {"eval_flag": True}) == {
         "azure": "nixos-image-azure-25.05.20250102.6df2492-x86_64-linux.vhd",
         "vmware": "nixos-image-vmware-25.05.20250102.6df2492-x86_64-linux.vmdk",
@@ -574,7 +574,7 @@ def test_repl(mock_run: Mock) -> None:
 
 @patch(get_qualified_name(n.run_wrapper, n), autospec=True)
 def test_repl_flake(mock_run: Mock) -> None:
-    n.repl_flake(m.Flake(Path("flake.nix"), "myAttr"), {"nix_flag": True})
+    n.repl_flake(m.Flake("flake.nix", "myAttr"), {"nix_flag": True})
     # See nixos-rebuild-ng.tests.repl for a better test,
     # this is mostly for sanity check
     assert mock_run.call_count == 1