nixos-rebuild-ng: do not try to copy closure when running dry-build (#444166)

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

@@ -192,12 +192,15 @@ def _build_system(
                 build_flags=build_flags | {"no_out_link": no_link, "dry_run": dry_run},
             )
 
-    nix.copy_closure(
-        path_to_config,
-        to_host=target_host,
-        from_host=build_host,
-        copy_flags=copy_flags,
-    )
+    # In dry_run mode there is nothing to copy
+    # https://github.com/NixOS/nixpkgs/issues/444156
+    if not dry_run:
+        nix.copy_closure(
+            path_to_config,
+            to_host=target_host,
+            from_host=build_host,
+            copy_flags=copy_flags,
+        )
 
     return path_to_config
 

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

@@ -985,6 +985,74 @@ def test_execute_build(mock_run: Mock, tmp_path: Path) -> None:
     )
 
 
+@patch("subprocess.run", autospec=True)
+def test_execute_build_dry_run_build_and_target_remote(
+    mock_run: Mock, tmp_path: Path
+) -> None:
+    config_path = tmp_path / "test"
+    config_path.touch()
+    mock_run.side_effect = [
+        CompletedProcess([], 0, str(config_path)),
+        CompletedProcess([], 0),
+        CompletedProcess([], 0, str(config_path)),
+    ]
+
+    nr.execute(
+        [
+            "nixos-rebuild",
+            "dry-build",
+            "--flake",
+            "/path/to/config#hostname",
+            "--build-host",
+            "user@build-host",
+            "--target-host",
+            "user@target-host",
+        ]
+    )
+
+    assert mock_run.call_count == 3
+    mock_run.assert_has_calls(
+        [
+            call(
+                [
+                    "nix",
+                    "--extra-experimental-features",
+                    "nix-command flakes",
+                    "eval",
+                    "--raw",
+                    '/path/to/config#nixosConfigurations."hostname".config.system.build.toplevel.drvPath',
+                ],
+                check=True,
+                stdout=PIPE,
+                **DEFAULT_RUN_KWARGS,
+            ),
+            call(
+                ["nix-copy-closure", "--to", "user@build-host", config_path],
+                check=True,
+                **DEFAULT_RUN_KWARGS,
+            ),
+            call(
+                [
+                    "ssh",
+                    *nr.process.SSH_DEFAULT_OPTS,
+                    "user@build-host",
+                    "--",
+                    "nix",
+                    "--extra-experimental-features",
+                    "'nix-command flakes'",
+                    "build",
+                    f"'{config_path}^*'",
+                    "--print-out-paths",
+                    "--dry-run",
+                ],
+                check=True,
+                stdout=PIPE,
+                **DEFAULT_RUN_KWARGS,
+            ),
+        ]
+    )
+
+
 @patch("subprocess.run", autospec=True)
 def test_execute_test_flake(mock_run: Mock, tmp_path: Path) -> None:
     config_path = tmp_path / "test"