Add regression test for install_cargo_config PermissionError path

.github/workflows/build-native-action.yml

@@ -307,6 +307,7 @@ jobs:
       - uses: actions/checkout@v3
 
       - name: Set up Python 3.11
+        id: setup-python
         uses: actions/setup-python@v5
         with:
           python-version: '3.11'
@@ -339,6 +340,16 @@ jobs:
           # SSE intrinsics in <wchar.h> that break C compiles under the
           # v140 toolset Python 3.10/3.11 PCbuild targets.
           WindowsTargetPlatformVersion: "10.0.19041.0"
+          # CPython 3.10's PCbuild\find_python.bat only probes `py -3.9`
+          # / `py -3.8` before falling back to a nuget-based install of
+          # pythonx86. That nuget path is currently broken on
+          # windows-2022 ("The system cannot execute the specified
+          # program" from `nuget install pythonx86`). Point HOST_PYTHON
+          # at the setup-python interpreter so find_python.bat accepts
+          # it directly (checked before the py-launcher / nuget path)
+          # and never invokes nuget. 3.11+ probe newer py versions and
+          # are unaffected, but setting HOST_PYTHON for them is a no-op.
+          HOST_PYTHON: ${{ steps.setup-python.outputs.python-path }}
         run: |
           python -m relenv build --no-pretty --arch=${{ matrix.arch }} --python=${{ steps.python-version.outputs.version }}
 

tests/test_runtime.py

@@ -175,6 +175,54 @@ def __init__(self, data: pathlib.Path) -> None:
     assert "x86_64-unknown-linux-gnu" in config_path.read_text()
 
 
+def test_install_cargo_config_toolchain_permission_error(
+    tmp_path: pathlib.Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    """
+    Regression for
+    https://github.com/saltstack/relenv/issues/252#issuecomment-4478458740.
+
+    ``common().get_toolchain()`` calls ``os.makedirs(DATA_DIR)`` and can raise
+    ``PermissionError`` under a non-root process whose install dir isn't
+    writable.  ``install_cargo_config`` catches the ``PermissionError`` but
+    then checks ``if not toolchain:``.  If the local ``toolchain`` isn't
+    initialized before the ``try:``, the check fires ``UnboundLocalError:
+    local variable 'toolchain' referenced before assignment`` — surfacing as
+    a noisy traceback from ``site.addpackage`` on every interpreter start.
+
+    ``install_cargo_config`` must degrade quietly (log via ``debug`` and
+    return) whether ``get_toolchain`` raises ``PermissionError`` or returns
+    ``None``.
+    """
+    monkeypatch.setattr(relenv.runtime.sys, "platform", "linux")
+    data_dir = tmp_path / "data"
+    data_dir.mkdir()
+
+    class StubDirs:
+        def __init__(self, data: pathlib.Path) -> None:
+            self.data = data
+
+    stub_dirs = StubDirs(data_dir)
+
+    def _raise_permission_error() -> pathlib.Path:
+        raise PermissionError("[Errno 13] Permission denied: '/opt/example/.local'")
+
+    stub_common = SimpleNamespace(
+        DATA_DIR=tmp_path,
+        work_dirs=lambda: stub_dirs,
+        get_triplet=lambda: "x86_64-linux-gnu",
+        get_toolchain=_raise_permission_error,
+    )
+    monkeypatch.setattr(relenv.runtime, "common", lambda: stub_common)
+
+    # Must not raise UnboundLocalError (or anything else).
+    relenv.runtime.install_cargo_config()
+
+    # And must not have written a cargo config, since there's no toolchain
+    # to point it at.
+    assert not (data_dir / "cargo" / "config.toml").exists()
+
+
 def test_build_shebang_value_error(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.setattr(relenv.runtime.sys, "RELENV", pathlib.Path("/rel"), raising=False)
     monkeypatch.setattr(

tests/test_verify_build.py

@@ -468,6 +468,17 @@ def test_pip_install_pyzmq(
     if pyzmq_version == "26.2.0" and sys.platform == "win32":
         pytest.xfail("vcredist not found as of 9/9/24")
 
+    if pyzmq_version == "26.2.0" and sys.platform == "linux":
+        # pyzmq 26.2.0's pyproject.toml uses scikit-build-core's
+        # `cmake.targets = ["pyzmq"]` option, which was renamed to
+        # `build.targets` in scikit-build-core 1.0.0 (released 2026-07-06).
+        # pyzmq 26.2.0 leaves scikit-build-core unpinned in build-system.requires,
+        # so pip picks up the newest release and the build errors out with:
+        #   ERROR: Use build.targets instead of cmake.targets for
+        #   scikit-build-core >= 0.10
+        # Fixed upstream in pyzmq 26.4.0 (which uses build.targets).
+        pytest.xfail("pyzmq 26.2.0 incompatible with scikit-build-core >= 1.0")
+
     if pyzmq_version == "26.4.0" and sys.platform == "win32":
         pytest.xfail("Needs troubleshooting 4/12/25")