Built in discovery class is always preferred over plugin supplied cla…

…sses (#2088)

docs/changelog/2087.bugfix.rst

@@ -0,0 +1 @@
+Built in discovery class is always preferred over plugin supplied classes.

src/virtualenv/run/plugin/discovery.py

@@ -13,10 +13,13 @@ def get_discover(parser, args):
         title="discovery",
         description="discover and provide a target interpreter",
     )
+    choices = _get_default_discovery(discover_types)
+    # prefer the builtin if present, otherwise fallback to first defined type
+    choices = sorted(choices, key=lambda a: 0 if a == "builtin" else 1)
     discovery_parser.add_argument(
         "--discovery",
-        choices=_get_default_discovery(discover_types),
-        default=next(i for i in discover_types.keys()),
+        choices=choices,
+        default=next(iter(choices)),
         required=False,
         help="interpreter discovery method",
     )

tests/unit/config/cli/test_parser.py

@@ -44,3 +44,14 @@ def test_reset_app_data_does_not_conflict_clear():
     session_via_cli(["--clear", "venv"], options=options)
     assert options.clear is True
     assert options.reset_app_data is False
+
+
+def test_builtin_discovery_class_preferred(mocker):
+    mocker.patch(
+        "virtualenv.run.plugin.discovery._get_default_discovery",
+        return_value=["pluginA", "pluginX", "builtin", "Aplugin", "Xplugin"],
+    )
+
+    options = VirtualEnvOptions()
+    session_via_cli(["venv"], options=options)
+    assert options.discovery == "builtin"