Better handling of base executable not found #1515

Improve the base executable discovery mechanism:

- print at debug level why we refuse some candidates,
- when no candidates match exactly, instead of hard failing fallback to the closest match where the priority of matching attributes is python implementation, major version, minor version, architecture, patch version, release level and serial (this is to facilitate things to still work when the OS upgrade replace/upgrades the system python with a newer version than what the virtualenv host python was created with),
- always resolve system_executable information during the interpreter discovery, and the discovered environment is the system interpreter instead of the venv/virtualenv (this happened before lazily the first time we accessed and caused reporting that the created virtual environment is of type of the virtualenv host python version, instead of the system pythons version - these two can differ if the OS upgraded the system python underneath and the virtualenv host was created via copy),

1 files changed, 2 insertions, 1 deletions

diff --git a/tests/integration/test_zipapp.py b/tests/integration/test_zipapp.py
index 25e83fd..0d64ae8 100644
--- a/tests/integration/test_zipapp.py
+++ b/tests/integration/test_zipapp.py
@@ -7,11 +7,12 @@ import sys
 import pytest
 import six
 
-from virtualenv.discovery.py_info import CURRENT
+from virtualenv.discovery.py_info import PythonInfo
 from virtualenv.run import run_via_cli
 from virtualenv.util.path import Path
 
 HERE = Path(__file__).parent
+CURRENT = PythonInfo.current_system()
 
 
 @pytest.fixture(scope="session")