tests/f2: don't set NIX_STORE_DIR unconditionally

this is only needed on macos, and only for tests that build anything. on
linux it can actually *break* stuff due to unfortunate interactions with
store url parsing, which is required to work for any remote build tests.

Change-Id: Ic6f7e090f15e129fc365d7edc56cdbc1a5686047

tests/functional2/testlib/fixtures/env.py

@@ -136,11 +136,18 @@ class _Dirs:
     nix_state_dir: Path | None
     nix_conf_dir: Path | None
     nix_bin_dir: Path | None
-    nix_store_dir: Path | None
+    # this one *must not* be NIX_STORE_DIR, otherwise lix will pick it up
+    # and misconfigure itself. the config system is unbelievable bullshit
+    real_store_dir: Path | None
     cache_dir: Path | None
     xdg_cache_home: Path | None
     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)}
@@ -174,7 +181,7 @@ class ManagedEnv:
             nix_state_dir=self._get_dir("var/nix"),
             nix_conf_dir=self._get_dir("etc/nix"),
             nix_bin_dir=lix_bin,
-            nix_store_dir=self._get_dir("nix/store"),
+            real_store_dir=self._get_dir("nix/store"),
             cache_dir=self._get_dir("binary-cache"),
             xdg_cache_home=self._get_dir("test-home/.cache"),
             tmpdir=self._get_dir("tmp"),

tests/functional2/testlib/fixtures/nix.py

@@ -109,7 +109,7 @@ class Nix:
         """
         if self._settings is None:
             self._settings = NixSettings()
-            self._settings.store = f"local?root={self.env.dirs.test_root}&store=/nix/store"
+            self._settings.store = f"local?root={self.env.dirs.test_root}"
 
         return self._settings
 
@@ -134,7 +134,7 @@ class Nix:
                 build == "auto" and (argv[0] == "nix-build" or argv[1:2] == ["build"])
             ):
                 settings.store = None
-                settings.nix_store_dir = self.env.dirs.nix_store_dir
+                settings.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)
@@ -178,8 +178,8 @@ class Nix:
         """
         The actual NIX_STORE_DIR this Nix command uses.
         """
-        assert self.env.dirs.nix_store_dir is not None, "bug in ManagedEnv"
-        return self.env.dirs.nix_store_dir
+        assert self.env.dirs.real_store_dir is not None, "bug in ManagedEnv"
+        return self.env.dirs.real_store_dir
 
     def physical_store_path_for(self, path: str | Path) -> Path:
         """

tests/functional2/testlib/fixtures/test_env.py

@@ -21,7 +21,7 @@ def test_env_inits_defaults(tmp_path: Path):
 
     assert env.dirs.test_root == tmp_path
     assert env.dirs.home == tmp_path / "test-home"
-    assert env.dirs.nix_store_dir == tmp_path / "nix/store"
+    assert env.dirs.real_store_dir == tmp_path / "nix/store"
 
 
 def test_env_unknown_none(env: ManagedEnv):
@@ -94,11 +94,16 @@ def test_env_get_dir_works(env: ManagedEnv):
 
 
 def test_env_dirs_created(env: ManagedEnv):
-    fields = dataclasses.asdict(env.dirs).values()
+    fields = dataclasses.asdict(env.dirs).items()
     assert len(fields) > 1
-    for field in fields:
-        field: Path
-        assert field.exists()
+    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()
 
 
 def test_env_get_path_fails(env: ManagedEnv):
@@ -123,7 +128,7 @@ 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",
         "PATH",