From 2ec2c4af08612fff4b606ee636602da2f2905a4c Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Thu, 31 Jul 2025 05:31:56 +0000
Subject: [PATCH 1/2] fix: handle StopIteration in discovery

When no discovery plugins are found, the application would crash with a StopIteration. This change catches the StopIteration and raises a RuntimeError with a more informative message.

Fixes #2493
---
 docs/changelog/2493.bugfix.rst         |  3 +++
 src/virtualenv/run/plugin/discovery.py |  7 ++++++-
 tests/unit/config/test___main__.py     | 10 ++++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 docs/changelog/2493.bugfix.rst

diff --git a/docs/changelog/2493.bugfix.rst b/docs/changelog/2493.bugfix.rst
new file mode 100644
index 000000000..7a29f1771
--- /dev/null
+++ b/docs/changelog/2493.bugfix.rst
@@ -0,0 +1,3 @@
+When no discovery plugins are found, the application would crash with a StopIteration.
+This change catches the StopIteration and raises a RuntimeError with a more informative message.
+Contributed by :user:`esafak`.
\ No newline at end of file
diff --git a/src/virtualenv/run/plugin/discovery.py b/src/virtualenv/run/plugin/discovery.py
index a963042d0..5e8b2392f 100644
--- a/src/virtualenv/run/plugin/discovery.py
+++ b/src/virtualenv/run/plugin/discovery.py
@@ -16,10 +16,15 @@ def get_discover(parser, args):
     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)
+    try:
+        default_discovery = next(iter(choices))
+    except StopIteration as e:
+        msg = "No discovery plugin found. Try reinstalling virtualenv to fix this issue."
+        raise RuntimeError(msg) from e
     discovery_parser.add_argument(
         "--discovery",
         choices=choices,
-        default=next(iter(choices)),
+        default=default_discovery,
         required=False,
         help="interpreter discovery method",
     )
diff --git a/tests/unit/config/test___main__.py b/tests/unit/config/test___main__.py
index b7c1850c5..0bd2569d6 100644
--- a/tests/unit/config/test___main__.py
+++ b/tests/unit/config/test___main__.py
@@ -52,6 +52,16 @@ def test_fail_no_traceback(raise_on_session_done, tmp_path, capsys):
     assert err == "err\n"
 
 
+def test_discovery_fails_no_discovery_plugin(mocker, tmp_path, capsys):
+    mocker.patch("virtualenv.run.plugin.discovery.Discovery.entry_points_for", return_value={})
+    with pytest.raises(SystemExit) as context:
+        run_with_catch([str(tmp_path)])
+    assert context.value.code == 1
+    out, err = capsys.readouterr()
+    assert "RuntimeError: No discovery plugin found. Try reinstalling virtualenv to fix this issue." in out
+    assert not err
+
+
 def test_fail_with_traceback(raise_on_session_done, tmp_path, capsys):
     raise_on_session_done(TypeError("something bad"))
 

From 777a191f9b16a07b533bbf941be7699d6098b286 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Thu, 31 Jul 2025 15:01:16 +0000
Subject: [PATCH 2/2] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 docs/changelog/2493.bugfix.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/changelog/2493.bugfix.rst b/docs/changelog/2493.bugfix.rst
index 7a29f1771..1ac87c85a 100644
--- a/docs/changelog/2493.bugfix.rst
+++ b/docs/changelog/2493.bugfix.rst
@@ -1,3 +1,3 @@
 When no discovery plugins are found, the application would crash with a StopIteration.
 This change catches the StopIteration and raises a RuntimeError with a more informative message.
-Contributed by :user:`esafak`.
\ No newline at end of file
+Contributed by :user:`esafak`.