fix(nodeenv): warn when -p picks the activated virtualenv over its own

The activated VIRTUAL_ENV and the virtualenv nodeenv is installed in can
only differ when nodeenv is installed elsewhere, and then the choice is
ambiguous, so log which one is used and how to override it.

The three sys.prefix branches all resolved to the same value, they are
folded into a single check reused by the warning.

Author: ekalinin

nodeenv.py

@@ -1382,6 +1382,11 @@ def resolve_node_version(spec):
 
 def get_env_dir(args):
     if args.python_virtualenv:
+        # whether nodeenv itself is running inside a python virtualenv
+        in_virtualenv = (
+            hasattr(sys, 'real_prefix') or
+            (hasattr(sys, 'base_prefix') and sys.base_prefix != sys.prefix) or
+            'CONDA_PREFIX' in os.environ)
         if args.python_virtualenv is not True:
             res = args.python_virtualenv
             if not os.path.isdir(res):
@@ -1391,11 +1396,12 @@ def get_env_dir(args):
         # (pipx, pipsi, uv tool), so the activated one wins over sys.prefix
         elif os.environ.get('VIRTUAL_ENV'):
             res = os.environ['VIRTUAL_ENV']
-        elif hasattr(sys, 'real_prefix'):
-            res = sys.prefix
-        elif hasattr(sys, 'base_prefix') and sys.base_prefix != sys.prefix:
-            res = sys.prefix
-        elif 'CONDA_PREFIX' in os.environ:
+            if in_virtualenv and res != sys.prefix:
+                logger.warning(
+                    ' * Using activated virtualenv %s, not %s where nodeenv '
+                    'is installed, pass a directory to -p to override',
+                    res, sys.prefix)
+        elif in_virtualenv:
             res = sys.prefix
         else:
             logger.error('No python virtualenv is available')

tests/nodeenv_test.py

@@ -1761,9 +1761,43 @@ def test_with_python_virtualenv_prefers_virtual_env(self):
         env_dict = {'VIRTUAL_ENV': virtual_env}
         with mock.patch.object(sys, 'real_prefix', test_prefix, create=True), \
              mock.patch.object(sys, 'prefix', test_prefix), \
-             mock.patch.dict(os.environ, env_dict, clear=True):
+             mock.patch.dict(os.environ, env_dict, clear=True), \
+             mock.patch.object(nodeenv.logger, 'warning') as mck:
             result = nodeenv.get_env_dir(args)
             assert result == virtual_env
+            # the ignored virtualenv is not silently dropped
+            assert mck.call_count == 1
+            assert mck.call_args[0][1:] == (virtual_env, test_prefix)
+
+    def test_with_python_virtualenv_same_venv_is_quiet(self):
+        """Test get_env_dir doesn't warn when both point to the same venv"""
+        args = mock.Mock()
+        args.python_virtualenv = True
+        test_prefix = '/path/to/venv'
+
+        env_dict = {'VIRTUAL_ENV': test_prefix}
+        with mock.patch.object(sys, 'real_prefix', test_prefix, create=True), \
+             mock.patch.object(sys, 'prefix', test_prefix), \
+             mock.patch.dict(os.environ, env_dict, clear=True), \
+             mock.patch.object(nodeenv.logger, 'warning') as mck:
+            result = nodeenv.get_env_dir(args)
+            assert result == test_prefix
+            mck.assert_not_called()
+
+    def test_with_python_virtualenv_system_python_is_quiet(self):
+        """Test get_env_dir doesn't warn when nodeenv runs system-wide"""
+        args = mock.Mock()
+        args.python_virtualenv = True
+        virtual_env = '/path/to/activated/venv'
+
+        env_dict = {'VIRTUAL_ENV': virtual_env}
+        with mock.patch.object(sys, 'prefix', '/usr'), \
+             mock.patch.object(sys, 'base_prefix', '/usr'), \
+             mock.patch.dict(os.environ, env_dict, clear=True), \
+             mock.patch.object(nodeenv.logger, 'warning') as mck:
+            result = nodeenv.get_env_dir(args)
+            assert result == virtual_env
+            mck.assert_not_called()
 
     def test_without_python_virtualenv(self):
         """Test get_env_dir when not using python virtualenv"""