fix(spec): handle dot-only version components

docs/changelog/147.bugfix.rst

@@ -0,0 +1,2 @@
+Treat specs with dot-only version components, such as ``python.``, as literal executable paths instead of raising
+``IndexError`` - by :user:`harbinresearcher`.

src/python_discovery/_py_spec.py

@@ -50,6 +50,9 @@ def _int_or_none(val: str | None) -> int | None:
 
 def _parse_version_parts(version: str) -> tuple[int | None, int | None, int | None]:
     versions = tuple(int(i) for i in version.split(".") if i)
+    if not versions:
+        msg = "version must contain a numeric component"
+        raise ValueError(msg)
     if len(versions) > _MAX_VERSION_PARTS:
         msg = "too many version parts"
         raise ValueError(msg)

tests/test_discovery.py

@@ -100,9 +100,10 @@ def test_discovery_fallback_fail(session_cache: DiskCache, caplog: pytest.LogCap
     assert "accepted" not in caplog.text
 
 
-def test_discovery_fallback_ok(session_cache: DiskCache, caplog: pytest.LogCaptureFixture) -> None:
+@pytest.mark.parametrize("missing", ["magic-one", "python."])
+def test_discovery_fallback_ok(missing: str, session_cache: DiskCache, caplog: pytest.LogCaptureFixture) -> None:
     caplog.set_level(logging.DEBUG)
-    result = get_interpreter(["magic-one", sys.executable], cache=session_cache)
+    result = get_interpreter([missing, sys.executable], cache=session_cache)
     assert result is not None, caplog.text
     assert result.executable == sys.executable, caplog.text
     assert "accepted" in caplog.text

tests/test_py_spec.py

@@ -13,8 +13,8 @@
     from pathlib import Path
 
 
-def test_bad_py_spec() -> None:
-    text = "python2.3.4.5"
+@pytest.mark.parametrize("text", ["python2.3.4.5", ".", "..", "...", "python.", "cpython..", "pypy..."])
+def test_bad_py_spec(text: str) -> None:
     spec = PythonSpec.from_string_spec(text)
     assert text in repr(spec)
     assert spec.str_spec == text