nix-update: make compatible with nixUnstable

nix_update/__init__.py

@@ -7,7 +7,7 @@ from typing import NoReturn, Optional
 from .eval import Package
 from .options import Options
 from .update import update
-from .utils import run
+from .utils import run, is_nix_flakes
 
 
 def die(msg: str) -> NoReturn:
@@ -48,14 +48,13 @@ def parse_args() -> Options:
 
 
 def nix_shell(options: Options) -> None:
-    with tempfile.NamedTemporaryFile(mode="w") as f:
-        f.write(
-            f"""
-        with import {options.import_path}; mkShell {{ buildInputs = [ {options.attribute} ]; }}
-        """
-        )
-        f.flush()
-        run(["nix-shell", f.name], stdout=None, check=False)
+    import_path = os.path.realpath(options.import_path)
+    expr = f"with import {import_path} {{}}; mkShell {{ buildInputs = [ {options.attribute} ]; }}"
+    with tempfile.TemporaryDirectory() as d:
+        path = os.path.join(d, "default.nix")
+        with open(path, "w") as f:
+            f.write(expr)
+        run(["nix-shell", path], stdout=None, check=False)
 
 
 def git_commit(git_dir: str, attribute: str, package: Package) -> None:
@@ -115,24 +114,26 @@ def validate_git_dir(import_path: str) -> str:
 
 
 def nix_run(options: Options) -> None:
+    if is_nix_flakes():
+        cmd = ["nix", "shell", "--experimental-features", "nix-command"]
+    else:
+        cmd = ["nix", "run"]
     run(
-        ["nix", "run", "-f", options.import_path, options.attribute],
-        stdout=None,
-        check=False,
+        cmd + ["-f", options.import_path, options.attribute], stdout=None, check=False,
     )
 
 
 def nix_build(options: Options) -> None:
+    cmd = ["nix", "build"]
+    if is_nix_flakes():
+        cmd += ["--experimental-features", "nix-command"]
     run(
-        ["nix", "build", "-f", options.import_path, options.attribute],
-        stdout=None,
-        check=False,
+        cmd + ["-f", options.import_path, options.attribute], stdout=None, check=False,
     )
 
 
 def main() -> None:
     options = parse_args()
-
     if not os.path.exists(options.import_path):
         die(f"path {options.import_path} does not exists")
 

nix_update/eval.py

@@ -4,7 +4,7 @@ from typing import List, Optional
 
 from .errors import UpdateError
 from .options import Options
-from .utils import run
+from .utils import run, is_nix_flakes
 
 
 @dataclass
@@ -48,9 +48,21 @@ def eval_expression(import_path: str, attr: str) -> str:
 
 
 def eval_attr(opts: Options) -> Package:
-    res = run(
-        ["nix", "eval", "--json", eval_expression(opts.import_path, opts.attribute)]
-    )
+    expr = eval_expression(opts.import_path, opts.attribute)
+    if is_nix_flakes():
+        cmd = [
+            "nix",
+            "eval",
+            "--json",
+            "--impure",
+            "--experimental-features",
+            "nix-command",
+            "--expr",
+            expr,
+        ]
+    else:
+        cmd = ["nix", "eval", "--json", expr]
+    res = run(cmd)
     out = json.loads(res.stdout)
     package = Package(**out)
     if package.old_version == "":

nix_update/utils.py

@@ -3,6 +3,7 @@ import subprocess
 import sys
 from pathlib import Path
 from typing import IO, Any, Callable, List, Optional, Union
+from functools import lru_cache
 
 HAS_TTY = sys.stdout.isatty()
 ROOT = Path(os.path.dirname(os.path.realpath(__file__)))
@@ -22,6 +23,15 @@ warn = color_text(31, file=sys.stderr)
 info = color_text(32)
 
 
+@lru_cache(maxsize=None)
+def is_nix_flakes() -> bool:
+    try:
+        subprocess.run(["nix", "flake", "--help"], stdout=subprocess.DEVNULL)
+    except subprocess.CalledProcessError:
+        return False
+    return True
+
+
 def run(
     command: List[str],
     cwd: Optional[Union[Path, str]] = None,