🐛 fix(py-info): detect equivalent base prefixes (#219)

Author: gaborbernat

docs/changelog/219.bugfix.rst

@@ -0,0 +1 @@
+Stop repeated interpreter queries when a virtual environment reports the same base prefix with different path spellings.

src/python_discovery/_py_info.py

@@ -10,6 +10,7 @@
 import sys
 from collections import OrderedDict
 from itertools import product
+from os.path import normcase, realpath
 from string import digits
 from typing import TYPE_CHECKING, ClassVar, Final, NamedTuple, TypedDict
 
@@ -462,7 +463,8 @@ def resolve_to_system(cls, cache: PyInfoCache | None, target: PythonInfo) -> Pyt
         prefixes = OrderedDict()
         while target.system_executable is None:
             prefix = target.real_prefix or target.base_prefix or target.prefix
-            if prefix in prefixes:
+            prefix_key = normcase(realpath(prefix))
+            if prefix_key in prefixes:
                 if len(prefixes) == 1:
                     _LOGGER.info("%r links back to itself via prefixes", target)
                     target.system_executable = target.executable
@@ -472,7 +474,7 @@ def resolve_to_system(cls, cache: PyInfoCache | None, target: PythonInfo) -> Pyt
                 _LOGGER.error("%d: prefix=%s, info=%r", len(prefixes) + 1, prefix, target)
                 msg = "prefixes are causing a circle {}".format("|".join(prefixes.keys()))
                 raise RuntimeError(msg)
-            prefixes[prefix] = target
+            prefixes[prefix_key] = target
             target = target.discover_exe(cache, prefix=prefix, exact=False)
         if target.executable != target.system_executable:
             resolved = cls.from_exe(target.system_executable, cache)

tests/test_py_info_extra.py

@@ -168,6 +168,21 @@ def test_resolve_to_system_single_prefix_self_link(mocker: MockerFixture, caplog
     assert any("links back to itself" in r.message for r in caplog.records)
 
 
+def test_resolve_to_system_repeated_prefix_with_parent_segments(tmp_path: Path, mocker: MockerFixture) -> None:
+    (tmp_path / "child").mkdir()
+    target = PythonInfo()
+    target.system_executable = target.real_prefix = None
+    target.base_prefix = str(tmp_path)
+    repeated = PythonInfo()
+    repeated.system_executable = repeated.real_prefix = None
+    repeated.base_prefix = str(tmp_path / "child" / "..")
+    mocker.patch.object(PythonInfo, "discover_exe", return_value=repeated)
+
+    result = PythonInfo.resolve_to_system(None, target)
+
+    assert result.system_executable == repeated.executable
+
+
 def test_discover_exe_cache_hit() -> None:
     info = copy.deepcopy(CURRENT)
     cached = copy.deepcopy(CURRENT)