🐛 fix(py_info): stop venv lookups rewriting each other's executable

docs/changelog/+cached-info-copies.bugfix.rst

@@ -0,0 +1,2 @@
+Stop a venv lookup from rewriting the ``executable`` of earlier results, ``PythonInfo.current()`` and
+``PythonInfo.current_system()`` when they share its base interpreter.

src/python_discovery/_py_info.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import copy
 import json
 import logging
 import os
@@ -475,7 +476,10 @@ def resolve_to_system(cls, cache: PyInfoCache | None, target: PythonInfo) -> Pyt
             resolved = cls.from_exe(target.system_executable, cache)
             if resolved is not None:
                 target = resolved
-        target.executable = start_executable
+        if target.executable != start_executable:
+            # the cache hands every lookup of this base the same object, so point a copy at the start executable
+            target = copy.copy(target)
+            target.executable = start_executable
         return target
 
     _cache_exe_discovery: ClassVar[dict[tuple[str, bool], PythonInfo]] = {}

tests/test_discovery.py

@@ -167,6 +167,18 @@ def test_discovery_absolute_path_with_try_first(
     assert Path(interpreter.executable) == good_exe
 
 
+def test_discovery_venvs_on_one_base_keep_their_executable(tmp_path: Path, session_cache: DiskCache) -> None:
+    scripts_dir = "Scripts" if IS_WIN else "bin"
+    exe_name = "python.exe" if IS_WIN else "python"
+    exes = [tmp_path / name / scripts_dir / exe_name for name in ("a", "b")]
+    for exe in exes:
+        subprocess.check_call([sys.executable, "-m", "venv", "--without-pip", str(exe.parents[1])])
+
+    found = [get_interpreter(str(exe), cache=session_cache) for exe in exes]
+
+    assert [Path(info.executable) for info in found if info is not None] == exes
+
+
 def test_discovery_via_path_with_file(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
     a_file = tmp_path / "a_file"
     a_file.touch()

tests/test_py_info_extra.py

@@ -439,3 +439,36 @@ def test_resolve_to_system_from_exe_returns_none(mocker: MockerFixture) -> None:
     mocker.patch.object(PythonInfo, "from_exe", return_value=None)
     result = PythonInfo.resolve_to_system(None, target)
     assert result.executable == "/some/venv/python"
+
+
+@pytest.mark.parametrize(
+    "system_executable",
+    [
+        pytest.param("/some/system/python", id="resolved"),
+        pytest.param(None, id="discovered"),
+    ],
+)
+def test_resolve_to_system_leaves_shared_info_untouched(mocker: MockerFixture, system_executable: str | None) -> None:
+    shared = copy.deepcopy(CURRENT)
+    shared.system_executable = shared.executable = "/some/system/python"
+    mocker.patch.object(PythonInfo, "from_exe", return_value=shared)
+    mocker.patch.object(PythonInfo, "discover_exe", return_value=shared)
+
+    results: list[PythonInfo] = []
+    for venv in ("/some/venv-a", "/some/venv-b"):
+        target = copy.deepcopy(CURRENT)
+        target.system_executable = system_executable
+        target.real_prefix, target.base_prefix, target.executable = None, venv, f"{venv}/python"
+        results.append(PythonInfo.resolve_to_system(None, target))
+
+    assert [(info.executable, info.system_executable) for info in results] == [
+        ("/some/venv-a/python", "/some/system/python"),
+        ("/some/venv-b/python", "/some/system/python"),
+    ]
+    assert shared.executable == "/some/system/python"
+
+
+def test_resolve_to_system_returns_target_when_executable_unchanged() -> None:
+    target = copy.deepcopy(CURRENT)
+    target.system_executable = target.executable = "/some/system/python"
+    assert PythonInfo.resolve_to_system(None, target) is target