feat: add session.noxfile and add tests

Signed-off-by: Henry Schreiner <[email protected]>

nox/sessions.py

@@ -198,6 +198,16 @@ def virtualenv(self) -> ProcessEnv:
             raise ValueError("A virtualenv has not been created for this session")
         return venv
 
+    @property
+    def noxfile(self) -> pathlib.Path:
+        """The path to the Noxfile that defines this session.
+
+        If the noxfile is a symlink, this does not resolve that last symlink; it
+        has been resolved up to that point. Use `session.noxfile.resolve()` to
+        get the original file path.
+        """
+        return pathlib.Path(self._runner.global_config.noxfile)
+
     @property
     def venv_backend(self) -> str:
         """The venv_backend selected."""

tests/resources/orig_dir/noxfile.py

@@ -0,0 +1,17 @@
+from pathlib import Path
+
+import nox
+
+DIR = Path(__file__).parent.resolve()
+
+
+@nox.session(venv_backend="none", default=False)
+def orig(session: nox.Session) -> None:
+    assert Path("orig_file.txt").exists()
+
+
+@nox.session(venv_backend="none", default=False)
+def sym(session: nox.Session) -> None:
+    assert Path("sym_file.txt").exists()
+
+    assert session.noxfile.resolve().parent.joinpath("orig_file.txt").exists()

tests/resources/sym_dir/noxfile.py

@@ -0,0 +1 @@
+../orig_dir/noxfile.py

tests/test_main.py

@@ -16,6 +16,7 @@
 
 import contextlib
 import os
+import subprocess
 import sys
 from importlib import metadata
 from pathlib import Path
@@ -928,3 +929,25 @@ def test_noxfile_options_cant_be_set():
 def test_noxfile_options_cant_be_set_long():
     with pytest.raises(AttributeError, match="i_am_clearly_not_an_option"):
         nox.options.i_am_clearly_not_an_option = True
+
+
+def test_symlink_orig(monkeypatch):
+    monkeypatch.chdir(Path(RESOURCES) / "orig_dir")
+    subprocess.run([sys.executable, "-m", "nox", "-s", "orig"], check=True)
+
+
+def test_symlink_orig_not(monkeypatch):
+    monkeypatch.chdir(Path(RESOURCES) / "orig_dir")
+    res = subprocess.run([sys.executable, "-m", "nox", "-s", "sym"], check=False)
+    assert res.returncode == 1
+
+
+def test_symlink_sym(monkeypatch):
+    monkeypatch.chdir(Path(RESOURCES) / "sym_dir")
+    subprocess.run([sys.executable, "-m", "nox", "-s", "sym"], check=True)
+
+
+def test_symlink_sym_not(monkeypatch):
+    monkeypatch.chdir(Path(RESOURCES) / "sym_dir")
+    res = subprocess.run([sys.executable, "-m", "nox", "-s", "orig"], check=False)
+    assert res.returncode == 1