Monkeypatch Apport excepthook (#88)

CHANGES.rst

@@ -3,6 +3,12 @@ Version history
 
 This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
 
+**UNRELEASED**
+
+- Added special monkeypatching if `Apport <https://github.com/canonical/apport>`_ has
+  overridden ``sys.excepthook`` so it will format exception groups correctly
+  (PR by John Litborn)
+
 **1.1.3**
 
 - ``catch()`` now raises a ``TypeError`` if passed an async exception handler instead of

src/exceptiongroup/_formatting.py

@@ -359,6 +359,46 @@ def format_exception_only(self):
     )
     sys.excepthook = exceptiongroup_excepthook
 
+# Ubuntu's system Python has a sitecustomize.py file that imports
+# apport_python_hook and replaces sys.excepthook.
+#
+# The custom hook captures the error for crash reporting, and then calls
+# sys.__excepthook__ to actually print the error.
+#
+# We don't mind it capturing the error for crash reporting, but we want to
+# take over printing the error. So we monkeypatch the apport_python_hook
+# module so that instead of calling sys.__excepthook__, it calls our custom
+# hook.
+#
+# More details: https://github.com/python-trio/trio/issues/1065
+if getattr(sys.excepthook, "__name__", None) in (
+    "apport_excepthook",
+    # on ubuntu 22.10 the hook was renamed to partial_apport_excepthook
+    "partial_apport_excepthook",
+):
+    # patch traceback like above
+    traceback.TracebackException.__init__ = (  # type: ignore[assignment]
+        PatchedTracebackException.__init__
+    )
+    traceback.TracebackException.format = (  # type: ignore[assignment]
+        PatchedTracebackException.format
+    )
+    traceback.TracebackException.format_exception_only = (  # type: ignore[assignment]
+        PatchedTracebackException.format_exception_only
+    )
+
+    from types import ModuleType
+
+    import apport_python_hook
+
+    assert sys.excepthook is apport_python_hook.apport_excepthook
+
+    # monkeypatch the sys module that apport has imported
+    fake_sys = ModuleType("exceptiongroup_fake_sys")
+    fake_sys.__dict__.update(sys.__dict__)
+    fake_sys.__excepthook__ = exceptiongroup_excepthook
+    apport_python_hook.sys = fake_sys
+
 
 @singledispatch
 def format_exception_only(__exc: BaseException) -> List[str]:

tests/apport_excepthook.py

@@ -0,0 +1,13 @@
+# The apport_python_hook package is only installed as part of Ubuntu's system
+# python, and not available in venvs. So before we can import it we have to
+# make sure it's on sys.path.
+import sys
+
+sys.path.append("/usr/lib/python3/dist-packages")
+import apport_python_hook  # noqa: E402 # unsorted import
+
+apport_python_hook.install()
+
+from exceptiongroup import ExceptionGroup  # noqa: E402 # unsorted import
+
+raise ExceptionGroup("msg1", [KeyError("msg2"), ValueError("msg3")])

tests/test_apport_monkeypatching.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+import os
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+
+import exceptiongroup
+
+
+def run_script(name: str) -> subprocess.CompletedProcess[bytes]:
+    exceptiongroup_path = Path(exceptiongroup.__file__).parent.parent
+    script_path = Path(__file__).parent / name
+
+    env = dict(os.environ)
+    print("parent PYTHONPATH:", env.get("PYTHONPATH"))
+    if "PYTHONPATH" in env:  # pragma: no cover
+        pp = env["PYTHONPATH"].split(os.pathsep)
+    else:
+        pp = []
+
+    pp.insert(0, str(exceptiongroup_path))
+    pp.insert(0, str(script_path.parent))
+    env["PYTHONPATH"] = os.pathsep.join(pp)
+    print("subprocess PYTHONPATH:", env.get("PYTHONPATH"))
+
+    cmd = [sys.executable, "-u", str(script_path)]
+    print("running:", cmd)
+    completed = subprocess.run(
+        cmd, env=env, stdout=subprocess.PIPE, stderr=subprocess.STDOUT
+    )
+    print("process output:")
+    print(completed.stdout.decode("utf-8"))
+    return completed
+
+
+@pytest.mark.skipif(
+    sys.version_info > (3, 11),
+    reason="No patching is done on Python >= 3.11",
+)
+@pytest.mark.skipif(
+    not Path("/usr/lib/python3/dist-packages/apport_python_hook.py").exists(),
+    reason="need Ubuntu with python3-apport installed",
+)
+def test_apport_excepthook_monkeypatch_interaction():
+    completed = run_script("apport_excepthook.py")
+    stdout = completed.stdout.decode("utf-8")
+    file = Path(__file__).parent / "apport_excepthook.py"
+    assert stdout == (
+        f"""\
+  + Exception Group Traceback (most recent call last):
+  |   File "{file}", line 13, in <module>
+  |     raise ExceptionGroup("msg1", [KeyError("msg2"), ValueError("msg3")])
+  | exceptiongroup.ExceptionGroup: msg1 (2 sub-exceptions)
+  +-+---------------- 1 ----------------
+    | KeyError: 'msg2'
+    +---------------- 2 ----------------
+    | ValueError: msg3
+    +------------------------------------
+"""
+    )