don't rely on NIX_PATH

Nix does not respect `NIX_PATH` when the `nix-path` setting in nix.conf
is set, which breaks the `nix-store --verify-path` due to `<nixpkgs>`
diverging from the temporary nixpkgs created by nixpkgs-review.

nixpkgs_review/builddir.py

@@ -58,12 +58,10 @@ def __init__(self, name: str) -> None:
 
         self.worktree_dir = self.path.joinpath("nixpkgs")
         self.worktree_dir.mkdir()
-        self.worktree_dir = self.worktree_dir
 
-        os.environ["NIX_PATH"] = self.nixpkgs_path()
-
-    def nixpkgs_path(self) -> str:
-        return f"nixpkgs={self.worktree_dir}:nixpkgs-overlays={self.overlay.path}"
+        self.nix_path = (
+            f"nixpkgs={self.worktree_dir} nixpkgs-overlays={self.overlay.path}"
+        )
 
     def __enter__(self) -> "Builddir":
         return self

nixpkgs_review/cli/post_result.py

@@ -1,6 +1,5 @@
 import argparse
 import os
-import subprocess
 import sys
 from pathlib import Path
 
@@ -17,14 +16,7 @@ def post_result_command(args: argparse.Namespace) -> None:
         sys.exit(1)
     pr = int(pr_env)
 
-    output = subprocess.run(
-        ["nix-instantiate", "--find-file", "nixpkgs"],
-        check=True,
-        stdout=subprocess.PIPE,
-        text=True,
-    ).stdout.strip()
-    nixpkgs_path = Path(output)
-    report = nixpkgs_path.parent.joinpath("report.md")
+    report = Path(os.environ["NIXPKGS_REVIEW_ROOT"]) / "report.md"
     if not report.exists():
         warn(f"Report not found in {report}. Are you in a nixpkgs-review nix-shell?")
         sys.exit(1)

nixpkgs_review/nix.py

@@ -46,6 +46,7 @@ def nix_shell(
     cache_directory: Path,
     system: str,
     build_graph: str,
+    nix_path: str,
     nixpkgs_config: Path,
     run: Optional[str] = None,
     sandbox: bool = False,
@@ -57,15 +58,17 @@ def nix_shell(
     shell = cache_directory.joinpath("shell.nix")
     write_shell_expression(shell, attrs, system, nixpkgs_config)
     if sandbox:
-        args = _nix_shell_sandbox(nix_shell, shell, nixpkgs_config)
+        args = _nix_shell_sandbox(nix_shell, shell, nix_path, nixpkgs_config)
     else:
-        args = [nix_shell, str(shell)]
+        args = [nix_shell, str(shell), "--nix-path", nix_path]
     if run:
         args.extend(["--run", run])
     sh(args, cwd=cache_directory, check=False)
 
 
-def _nix_shell_sandbox(nix_shell: str, shell: Path, nixpkgs_config: Path) -> List[str]:
+def _nix_shell_sandbox(
+    nix_shell: str, shell: Path, nix_path: str, nixpkgs_config: Path
+) -> List[str]:
     if platform != "linux":
         raise RuntimeError("Sandbox mode is only available on Linux platforms.")
 
@@ -137,7 +140,7 @@ def tmpfs(path: Union[Path, str], dir: bool = True) -> List[str]:
         *bind(hub_config, try_=True),
         *bind(gh_config, try_=True),
     ]
-    return [bwrap, *bwrap_args, "--", nix_shell, str(shell)]
+    return [bwrap, *bwrap_args, "--", nix_shell, str(shell), "--nix-path", nix_path]
 
 
 def _nix_eval_filter(json: Dict[str, Any]) -> List[Attr]:
@@ -185,6 +188,7 @@ def nix_eval(
     attrs: Set[str],
     system: str,
     allow: AllowedFeatures,
+    nix_path: str,
 ) -> List[Attr]:
     attr_json = NamedTemporaryFile(mode="w+", delete=False)
     delete = True
@@ -199,6 +203,8 @@ def nix_eval(
             "--system",
             system,
             "eval",
+            "--nix-path",
+            nix_path,
             "--json",
             "--impure",
             "--allow-import-from-derivation"
@@ -233,13 +239,14 @@ def nix_build(
     system: str,
     allow: AllowedFeatures,
     build_graph: str,
+    nix_path: str,
     nixpkgs_config: Path,
 ) -> List[Attr]:
     if not attr_names:
         info("Nothing to be built.")
         return []
 
-    attrs = nix_eval(attr_names, system, allow)
+    attrs = nix_eval(attr_names, system, allow, nix_path)
     filtered = []
     for attr in attrs:
         if not (attr.broken or attr.blacklisted):
@@ -254,6 +261,8 @@ def nix_build(
     command = [
         build_graph,
         "build",
+        "--nix-path",
+        nix_path,
         "--extra-experimental-features",
         "nix-command" if allow.url_literals else "nix-command no-url-literals",
         "--no-link",

nixpkgs_review/review.py

@@ -151,7 +151,7 @@ def build_commit(
         self.git_worktree(base_commit)
 
         base_packages = list_packages(
-            str(self.worktree_dir()),
+            self.builddir.nix_path,
             self.system,
             self.allow,
         )
@@ -162,7 +162,7 @@ def build_commit(
             self.git_merge(reviewed_commit)
 
         merged_packages = list_packages(
-            str(self.worktree_dir()),
+            self.builddir.nix_path,
             self.system,
             self.allow,
             check_meta=True,
@@ -192,6 +192,7 @@ def build(self, packages: Set[str], args: str) -> List[Attr]:
             self.skip_packages_regex,
             self.system,
             self.allow,
+            self.builddir.nix_path,
         )
         return nix_build(
             packages,
@@ -200,6 +201,7 @@ def build(self, packages: Set[str], args: str) -> List[Attr]:
             self.system,
             self.allow,
             self.build_graph,
+            self.builddir.nix_path,
             self.nixpkgs_config,
         )
 
@@ -252,7 +254,7 @@ def start_review(
         print_result: bool = False,
     ) -> None:
         os.environ.pop("NIXPKGS_CONFIG", None)
-        os.environ["NIX_PATH"] = path.as_posix()
+        os.environ["NIXPKGS_REVIEW_ROOT"] = str(path)
         if pr:
             os.environ["PR"] = str(pr)
         report = Report(self.system, attr, self.extra_nixpkgs_config)
@@ -273,6 +275,7 @@ def start_review(
                 path,
                 self.system,
                 self.build_graph,
+                self.builddir.nix_path,
                 self.nixpkgs_config,
                 self.run,
                 self.sandbox,
@@ -342,7 +345,7 @@ def parse_packages_xml(stdout: IO[str]) -> List[Package]:
 
 
 def list_packages(
-    path: str,
+    nix_path: str,
     system: str,
     allow: AllowedFeatures,
     check_meta: bool = False,
@@ -355,7 +358,9 @@ def list_packages(
         "system",
         system,
         "-f",
-        path,
+        "<nixpkgs>",
+        "--nix-path",
+        nix_path,
         "-qaP",
         "--xml",
         "--out-path",
@@ -378,13 +383,14 @@ def package_attrs(
     package_set: Set[str],
     system: str,
     allow: AllowedFeatures,
+    nix_path: str,
     ignore_nonexisting: bool = True,
 ) -> Dict[str, Attr]:
     attrs: Dict[str, Attr] = {}
 
     nonexisting = []
 
-    for attr in nix_eval(package_set, system, allow):
+    for attr in nix_eval(package_set, system, allow, nix_path):
         if not attr.exists:
             nonexisting.append(attr.name)
         elif not attr.broken:
@@ -403,12 +409,14 @@ def join_packages(
     specified_packages: Set[str],
     system: str,
     allow: AllowedFeatures,
+    nix_path: str,
 ) -> Set[str]:
-    changed_attrs = package_attrs(changed_packages, system, allow)
+    changed_attrs = package_attrs(changed_packages, system, allow, nix_path)
     specified_attrs = package_attrs(
         specified_packages,
         system,
         allow,
+        nix_path,
         ignore_nonexisting=False,
     )
 
@@ -439,6 +447,7 @@ def filter_packages(
     skip_package_regexes: List[Pattern[str]],
     system: str,
     allow: AllowedFeatures,
+    nix_path: str,
 ) -> Set[str]:
     packages: Set[str] = set()
 
@@ -456,6 +465,7 @@ def filter_packages(
             specified_packages,
             system,
             allow,
+            nix_path,
         )
 
     for attr in changed_packages:

tests/test_github_actions.py

@@ -9,12 +9,14 @@
 @patch("urllib.request.urlopen")
 def test_post_result(mock_urlopen: MagicMock, helpers: Helpers) -> None:
     with helpers.nixpkgs() as nixpkgs:
+        root = nixpkgs.path.parent
+
         os.environ["PR"] = "1"
-        os.environ["NIX_PATH"] = f"nixpkgs={nixpkgs.path}"
         os.environ["GITHUB_TOKEN"] = "foo"
+        os.environ["NIXPKGS_REVIEW_ROOT"] = str(root)
         mock_urlopen.side_effect = [mock_open(read_data="{}")()]
 
-        report = nixpkgs.path.joinpath("..", "report.md")
+        report = root / "report.md"
         with open(report, "w") as f:
             f.write("")