fix(venv): respect base_python passed as absolute path (#69)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/tox_uv/_venv.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import json
+import os
 import sys
 from abc import ABC
 from functools import cached_property
@@ -21,6 +22,8 @@
 from tox.execute.request import StdinSource
 from tox.tox_env.python.api import Python, PythonInfo, VersionInfo
 from uv import find_uv_bin
+from virtualenv import app_data
+from virtualenv.discovery import cached_py_info
 from virtualenv.discovery.py_spec import PythonSpec
 
 from ._installer import UvInstaller
@@ -83,6 +86,18 @@ def _get_python(self, base_python: list[str]) -> PythonInfo | None:  # noqa: PLR
                     platform=sys.platform,
                     extra={},
                 )
+            if Path(base).is_absolute():
+                info = cached_py_info.from_exe(
+                    cached_py_info.PythonInfo, app_data.make_app_data(None, read_only=False, env=os.environ), base
+                )
+                return PythonInfo(
+                    implementation=info.implementation,
+                    version_info=VersionInfo(*info.version_info),
+                    version=info.version,
+                    is_64=info.architecture == 64,  # noqa: PLR2004
+                    platform=info.platform,
+                    extra={"executable": base},
+                )
             spec = PythonSpec.from_string_spec(base)
             return PythonInfo(
                 implementation=spec.implementation or "CPython",
@@ -124,8 +139,12 @@ def _default_pass_env(self) -> list[str]:
         return env
 
     def create_python_env(self) -> None:
-        base, imp = self.base_python.version_info, self.base_python.impl_lower
-        if (base.major, base.minor) == sys.version_info[:2] and (sys.implementation.name.lower() == imp):
+        base = self.base_python.version_info
+        imp = self.base_python.impl_lower
+        executable = self.base_python.extra.get("executable")
+        if executable:
+            version_spec = executable
+        elif (base.major, base.minor) == sys.version_info[:2] and (sys.implementation.name.lower() == imp):
             version_spec = sys.executable
         else:
             uv_imp = "" if (imp and imp == "cpython") else imp

tests/test_tox_uv_venv.py

@@ -4,14 +4,16 @@
 import os
 import os.path
 import pathlib
+import platform
 import subprocess  # noqa: S404
 import sys
 from configparser import ConfigParser
 from importlib.metadata import version
 from typing import TYPE_CHECKING
 
+import pytest
+
 if TYPE_CHECKING:
-    import pytest
     from tox.pytest import ToxProjectCreator
 
 
@@ -50,6 +52,68 @@ def test_uv_venv_spec_major_only(tox_project: ToxProjectCreator) -> None:
     result.assert_success()
 
 
+@pytest.fixture
+def other_interpreter_exe() -> pathlib.Path:  # pragma: no cover
+    """Returns an interpreter executable path that is not the exact same as `sys.executable`.
+
+    Necessary because `sys.executable` gets short-circuited when used as `base_python`."""
+
+    exe = pathlib.Path(sys.executable)
+    base_python: pathlib.Path | None = None
+    if exe.name == "python":
+        # python -> pythonX.Y
+        ver = sys.version_info
+        base_python = exe.with_name(f"python{ver.major}.{ver.minor}")
+    elif exe.name[-1].isdigit():
+        # python X[.Y] -> python
+        base_python = exe.with_name(exe.stem[:-1])
+    elif exe.suffix == ".exe":
+        # python.exe <-> pythonw.exe
+        base_python = (
+            exe.with_name(exe.stem[:-1] + ".exe") if exe.stem.endswith("w") else exe.with_name(exe.stem + "w.exe")
+        )
+    if not base_python or not base_python.is_file():
+        pytest.fail("Tried to pick a base_python that is not sys.executable, but failed.")
+    return base_python
+
+
+def test_uv_venv_spec_abs_path(tox_project: ToxProjectCreator, other_interpreter_exe: pathlib.Path) -> None:
+    project = tox_project({"tox.ini": f"[testenv]\npackage=skip\nbase_python={other_interpreter_exe}"})
+    result = project.run("-vv")
+    result.assert_success()
+
+
+def test_uv_venv_spec_abs_path_conflict_ver(
+    tox_project: ToxProjectCreator, other_interpreter_exe: pathlib.Path
+) -> None:
+    # py27 is long gone, but still matches the testenv capture regex, so we know it will fail
+    project = tox_project({"tox.ini": f"[testenv:py27]\npackage=skip\nbase_python={other_interpreter_exe}"})
+    result = project.run("-vv", "-e", "py27")
+    result.assert_failed()
+    assert f"failed with env name py27 conflicting with base python {other_interpreter_exe}" in result.out
+
+
+def test_uv_venv_spec_abs_path_conflict_impl(
+    tox_project: ToxProjectCreator, other_interpreter_exe: pathlib.Path
+) -> None:
+    env = "pypy" if platform.python_implementation() == "CPython" else "cpython"
+    project = tox_project({"tox.ini": f"[testenv:{env}]\npackage=skip\nbase_python={other_interpreter_exe}"})
+    result = project.run("-vv", "-e", env)
+    result.assert_failed()
+    assert f"failed with env name {env} conflicting with base python {other_interpreter_exe}" in result.out
+
+
+def test_uv_venv_spec_abs_path_conflict_platform(
+    tox_project: ToxProjectCreator, other_interpreter_exe: pathlib.Path
+) -> None:
+    ver = sys.version_info
+    env = f"py{ver.major}{ver.minor}-linux" if sys.platform == "win32" else f"py{ver.major}{ver.minor}-win32"
+    project = tox_project({"tox.ini": f"[testenv:{env}]\npackage=skip\nbase_python={other_interpreter_exe}"})
+    result = project.run("-vv", "-e", env)
+    result.assert_failed()
+    assert f"failed with env name {env} conflicting with base python {other_interpreter_exe}" in result.out
+
+
 def test_uv_venv_na(tox_project: ToxProjectCreator) -> None:
     project = tox_project({"tox.ini": "[testenv]\npackage=skip\nbase_python=1.0"})
     result = project.run("-vv")