f2: don't use diverted stores unless specifically requested

diverted stores are only necessary when the logical store paths of
objects matter for the test itself, such as for derivation hashes,
substitution from golden sample nars, or actual tests of the store
diversion functionality. all other tests can use undiverted stores
to run, especially since only linux can build in diverted a store.

Change-Id: I62f0907bdef9961609af22b610195fcec54c1e57

tests/functional2/build/test_fixed.py

@@ -1,4 +1,3 @@
-import sys
 import re
 from pathlib import Path
 
@@ -24,7 +23,7 @@ def impure_vars(env: ManagedEnv):
 def test_bad(nix: Nix):
     res = nix.nix_instantiate(["fixed.nix", "-A", "good.0"], build=True).run().ok()
     store_path = nix.nix_store(["-q", res.stdout_plain], build=True).run().ok().stdout_plain
-    path = Path(f"{nix.env.dirs.test_root}{store_path}" if sys.platform != "darwin" else store_path)
+    path = Path(store_path)
     assert not path.exists()
 
     # Building with the bad hash should produce the "good" output path as

tests/functional2/lang/test_lang.py

@@ -8,7 +8,7 @@ import yaml
 from _pytest.python import Metafunc
 
 from lang.lang_util import LangTest, fetch_all_lang_tests, LangTestRunner
-from testlib.fixtures.nix import Nix
+from testlib.fixtures.nix import Nix, with_diverted_store
 from testlib.fixtures.snapshot import Snapshot
 
 
@@ -92,6 +92,7 @@ def test_parse_fail(files: Path, nix: Nix, flags: list[str], snapshot: Callable[
     assert snapshot("err.exp") == stderr
 
 
+@with_diverted_store
 def test_eval_okay(files: Path, nix: Nix, flags: list[str], snapshot: Callable[[str], Snapshot]):
     nix_command = nix.nix_instantiate(["--eval", "--strict", *flags, files / "in.nix"], flake=True)
     result = nix_command.run().ok()
@@ -101,6 +102,7 @@ def test_eval_okay(files: Path, nix: Nix, flags: list[str], snapshot: Callable[[
     assert snapshot("err.exp") == stderr
 
 
+@with_diverted_store
 def test_eval_fail(files: Path, nix: Nix, flags: list[str], snapshot: Callable[[str], Snapshot]):
     nix_command = nix.nix_instantiate(
         ["--eval", "--strict", "--show-trace", *flags, files / "in.nix"], flake=True

tests/functional2/store/test_evil_nars.py

@@ -6,7 +6,7 @@ from pathlib import Path
 
 import pytest
 
-from testlib.fixtures.nix import Nix
+from testlib.fixtures.nix import Nix, with_diverted_store
 from testlib.nar import (
     DirectoryUnordered,
     NarItem,
@@ -102,6 +102,7 @@ EVIL_NARS: list[tuple[str, NarItem]] = [
 
 
 @pytest.mark.parametrize(("name", "nar"), EVIL_NARS, ids=next(zip(*EVIL_NARS)))
+@with_diverted_store
 def test_evil_nar(nix: Nix, name: str, nar: NarItem, logger: Logger):
     bio = BytesIO()
 

tests/functional2/store/test_http.py

@@ -6,7 +6,7 @@ import pytest
 
 from testlib.fixtures.file_helper import File, with_files
 from testlib.fixtures.http_server import http_server
-from testlib.fixtures.nix import Nix
+from testlib.fixtures.nix import Nix, with_diverted_store
 
 
 class HTTPStore:
@@ -101,6 +101,7 @@ def nars_from_narinfo_cache(db_path: Path) -> list[dict[str, str | bool]]:
 
 
 @with_files({"test-file": File("hello world")})
+@with_diverted_store
 def test_http_simple(nix: Nix, store: HTTPStore, files: Path):
     test_file = files / "test-file"
     result = nix.nix(cmd=["store", "add-file", test_file], flake=True).run()

tests/functional2/testlib/fixtures/env.py

@@ -154,10 +154,6 @@ class _Dirs:
     tmpdir: Path | None
     """used for nar caching"""
     nix_store_dir: Path | None = None
-    """
-    store dir override for building on macos *specifically*. do not
-    use or set this for any other purpose or many tests will break.
-    """
 
     def get_env_keys(self) -> set[str]:
         return {f.name.upper() for f in dataclasses.fields(self)}
@@ -194,6 +190,7 @@ class ManagedEnv:
             nix_conf_dir=self._get_dir("etc/nix"),
             nix_bin_dir=lix_bin,
             real_store_dir=self._get_dir("nix/store"),
+            nix_store_dir=self._get_dir("nix/store"),
             cache_dir=self._get_dir("test-binary-cache"),
             xdg_cache_home=self._get_dir("test-home/.cache"),
             tmpdir=self._get_dir("tmp"),

tests/functional2/testlib/fixtures/nix.py

@@ -147,11 +147,19 @@ class Nix:
         if self._settings is None:
             self._settings = NixSettings()
             self._settings.store = f"local?root={self.env.dirs.test_root}"
+            if sys.platform == "linux":
+                # sandbox build dir cannot be withing store dir. choose a short non-overlapping path.
+                self._settings.sandbox_build_dir = (
+                    "/build-f2" if self.env.dirs.test_root.parts[1] != "build-f2" else "/build.f2"
+                )
 
         return self._settings
 
     def nix_cmd(
-        self, argv: list[str], flake: bool = False, build: bool | Literal["auto"] = "auto"
+        self,
+        argv: list[str],
+        flake: bool = False,
+        build: bool | Literal["auto"] = "auto",  # noqa: ARG002
     ) -> Command:
         """
         Constructs a NixCommand with the appropriate settings.
@@ -161,17 +169,6 @@ class Nix:
         settings = self.settings.clone()
         if flake:
             settings.add_xp_feature("nix-command", "flakes")
-        # FIXME(rootile): Darwin needs special handling here, as it does not support (non-root) chroots...
-        #  Hence, it cannot build using a relocated store so we just use the local (aka global) store instead
-        #  This is kinda ugly but what else can one do
-        if sys.platform == "darwin":
-            if build is True or (
-                # argv[1:2] does not throw a key error on empty lists
-                # hence not crashing this check on an empty `nix.nix([])` call
-                build == "auto" and (argv[0] == "nix-build" or argv[1:2] == ["build"])
-            ):
-                settings.store = None
-                self.env.dirs.nix_store_dir = self.env.dirs.real_store_dir
 
         settings.to_env_overlay(self.env)
         return Command(argv=argv, exe=self._nix_executable, _env=self.env)
@@ -352,3 +349,19 @@ def nix(tmp_path: Path, env: ManagedEnv, logger: logging.Logger) -> Generator[Ni
     # for pytest to be able to delete the files during cleanup
     cmd = Command(argv=["chmod", "-R", "+w", str(tmp_path.absolute())], _env=env)
     cmd.run().ok()
+
+
+@pytest.fixture
+def enable_diverted_store(nix: Nix):
+    """
+    clear NIX_STORE_DIR, resetting it to the default (ie /nix/store).
+    this makes builds impossible on platforms that cannot bind-mount,
+    (e.g. macos) but it is important for eval result reproducibility.
+    while builds may not work, substitution should still be possible.
+    """
+    nix.env.dirs.nix_store_dir = None
+    nix.settings.sandbox_build_dir = None
+
+
+def with_diverted_store(func: Callable[[Any], None]) -> Callable[[Any], None]:
+    return pytest.mark.usefixtures("enable_diverted_store")(func)

tests/functional2/testlib/fixtures/test_env.py

@@ -98,13 +98,7 @@ def test_env_dirs_created(env: ManagedEnv):
     fields = dataclasses.asdict(env.dirs).items()
     assert len(fields) > 1
     for name, field in fields:
-        field: Path | None
-        # we never want to set NIX_STORE_DIR on linux due to unfortunate config ordering.
-        # creating a fresh env should always have it unset, it'll only be set when needed
-        if name == "nix_store_dir":
-            assert field is None
-        else:
-            field.exists()
+        field.exists()
 
 
 def test_env_get_path_fails(env: ManagedEnv):
@@ -129,6 +123,7 @@ def test_env_to_env(tmp_path: Path):
         "NIX_STATE_DIR",
         "NIX_CONF_DIR",
         "NIX_BIN_DIR",
+        "NIX_STORE_DIR",
         "REAL_STORE_DIR",
         "CACHE_DIR",
         "XDG_CACHE_HOME",