🐛 fix(discovery): search bare specs on PATH

docs/changelog/207.security.rst

@@ -0,0 +1,2 @@
+Bare interpreter names now search ``PATH`` without probing a matching file in the working directory. Use ``./name``
+when the working directory contains the intended interpreter.

docs/explanation.rst

@@ -13,9 +13,11 @@ order. It stops as soon as it finds an interpreter that matches your spec.
         Start["get_interpreter()"] --> AbsPath{"Is spec an<br>absolute path?"}
         AbsPath -->|Yes| TryAbs["Use path directly"]
         AbsPath -->|No| TryFirst["try_first_with paths"]
-        TryFirst --> RelPath{"Is spec a<br>relative path?"}
+        TryFirst --> RelPath{"Does spec name a<br>relative directory?"}
         RelPath -->|Yes| TryRel["Resolve relative to cwd"]
-        RelPath -->|No| Current["Current interpreter"]
+        RelPath -->|No| Bare{"Bare executable name?"}
+        Bare -->|Yes| PATH
+        Bare -->|No| Current["Current interpreter"]
         Current --> Win{"Windows?"}
         Win -->|Yes| PEP514["PEP 514 registry"]
         Win -->|No| PATH
@@ -329,7 +331,8 @@ A spec string follows the pattern ``[impl][version][t][d][-arch][-machine]``. Ev
 Order matters: the parts appear in the sequence shown above. Combine the ABI flags as ``python3.13td``
 (free-threaded then debug, the order CPython uses in ``sys.abiflags``), and keep ``-arch`` before
 ``-machine`` as in ``python3.13d-64-arm64``. Mixing ``d`` with ``-dbg`` in one spec, or swapping the arch
-and machine segments, leaves the string unrecognized, so it falls back to a literal executable-name match.
+and machine segments, leaves the string unrecognized, so it falls back to a literal executable-name match on ``PATH``.
+Only a spec with a directory component, such as ``./python3`` or ``venv/bin/python``, searches the working directory.
 
 **Full examples:**
 

src/python_discovery/_discovery.py

@@ -216,7 +216,8 @@ def _propose_explicit(
             yield PythonInfo.from_exe(exe_raw, cache, env=env), True
 
     if spec.path is not None:
-        if exe_raw := _check_exe(spec.path, tested_exes):  # pragma: no branch
+        # Unparsed bare names reach spec.path; only an explicit directory should search the working directory.
+        if os.path.dirname(spec.path) and (exe_raw := _check_exe(spec.path, tested_exes)):
             yield PythonInfo.from_exe(exe_raw, cache, env=env), True
     else:
         yield from _propose_current_and_windows(spec, cache, env, tested_exes)

tests/test_discovery.py

@@ -94,6 +94,25 @@ def test_relative_path(session_cache: DiskCache, monkeypatch: pytest.MonkeyPatch
     assert result is not None
 
 
+@pytest.mark.parametrize(
+    "name",
+    [
+        pytest.param("3.14.0rc1", id="prerelease"),
+        pytest.param("python3.13-arm64-64", id="swapped-platform"),
+        pytest.param("python_d", id="executable-name"),
+    ],
+)
+def test_bare_name_spec_does_not_probe_cwd(
+    name: str, tmp_path: Path, monkeypatch: pytest.MonkeyPatch, mocker: MockerFixture
+) -> None:
+    (tmp_path / name).touch(mode=0o755)
+    monkeypatch.chdir(tmp_path)
+    from_exe = mocker.patch("python_discovery._discovery.PythonInfo.from_exe", return_value=None)
+
+    assert get_interpreter(name, [], env={"PATH": "", "UV_PYTHON_INSTALL_DIR": str(tmp_path / "uv")}) is None
+    from_exe.assert_not_called()
+
+
 @pytest.mark.parametrize(
     "sep",
     [