Make Trio's excepthook play nicely with Ubuntu's excepthook

Fixes python-triogh-1065

.github/workflows/ci.yml

@@ -2,8 +2,6 @@ name: CI
 
 on:
  push:
- branches:
- - master
  pull_request:
 
 jobs:

ci.sh

@@ -407,6 +407,11 @@ else
  # Actual tests
  python -m pip install -r test-requirements.txt
 
+ # So we can run the test for our apport/excepthook interaction working
+ if [ -e /etc/lsb-release ] && grep -q Ubuntu /etc/lsb-release; then
+ echo "not installing python3-apport"
+ fi
+
  # If we're testing with a LSP installed, then it might break network
  # stuff, so wait until after we've finished setting everything else
  # up.

newsfragments/1065.bugfix.rst

@@ -0,0 +1,8 @@
+On Ubuntu systems, the system Python includes a custom
+unhandled-exception hook to perform `crash reporting
+<https://wiki.ubuntu.com/Apport>`__. Unfortunately, Trio wants to use
+the same hook to print nice `MultiError` tracebacks, causing a
+conflict. Previously, Trio would detect the conflict, print a warning,
+and you just wouldn't get nice `MultiError` tracebacks. Now, Trio has
+gotten clever enough to integrate its hook with Ubuntu's, so the two
+systems should Just Work together.

trio/_core/_multierror.py

@@ -434,8 +434,8 @@ def trio_excepthook(etype, value, tb):
  sys.stderr.write(chunk)
 
 
-IPython_handler_installed = False
-warning_given = False
+monkeypatched_or_warned = False
+
 if "IPython" in sys.modules:
  import IPython
  ip = IPython.get_ipython()
@@ -448,7 +448,7 @@ def trio_excepthook(etype, value, tb):
  "tracebacks.",
  category=RuntimeWarning
  )
- warning_given = True
+ monkeypatched_or_warned = True
  else:
 
  def trio_show_traceback(self, etype, value, tb, tb_offset=None):
@@ -457,15 +457,44 @@ def trio_show_traceback(self, etype, value, tb, tb_offset=None):
  trio_excepthook(etype, value, tb)
 
  ip.set_custom_exc((MultiError,), trio_show_traceback)
- IPython_handler_installed = True
+ monkeypatched_or_warned = True
 
 if sys.excepthook is sys.__excepthook__:
  sys.excepthook = trio_excepthook
-else:
- if not IPython_handler_installed and not warning_given:
- warnings.warn(
- "You seem to already have a custom sys.excepthook handler "
- "installed. I'll skip installing Trio's custom handler, but this "
- "means MultiErrors will not show full tracebacks.",
- category=RuntimeWarning
- )
+ monkeypatched_or_warned = True
+
+# Ubuntu's system Python has a sitecustomize.py file that import
+# 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 sys.excepthook.__name__ == "apport_excepthook":
+ import apport_python_hook
+ assert sys.excepthook is apport_python_hook.apport_excepthook
+
+ # Give it a descriptive name as a hint for anyone who's stuck trying to
+ # debug this mess later.
+ class TrioFakeSysModuleForApport:
+ pass
+
+ fake_sys = TrioFakeSysModuleForApport()
+ fake_sys.__dict__.update(sys.__dict__)
+ fake_sys.__excepthook__ = trio_excepthook
+ apport_python_hook.sys = fake_sys
+
+ monkeypatched_or_warned = True
+
+if not monkeypatched_or_warned:
+ warnings.warn(
+ "You seem to already have a custom sys.excepthook handler "
+ "installed. I'll skip installing Trio's custom handler, but this "
+ "means MultiErrors will not show full tracebacks.",
+ category=RuntimeWarning
+ )

trio/_core/tests/test_multierror.py

@@ -709,3 +709,26 @@ def test_ipython_custom_exc_handler():
  )
  # Make sure our other warning doesn't show up
  assert "custom sys.excepthook" not in completed.stdout.decode("utf-8")
+
+
+@slow
+@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")
+
+ # No warning
+ assert "custom sys.excepthook" not in stdout
+
+ # Proper traceback
+ assert_match_in_seq(
+ [
+ "Details of embedded",
+ "KeyError",
+ "Details of embedded",
+ "ValueError",
+ ], stdout
+ )

trio/_core/tests/test_multierror_scripts/apport_excepthook.py

@@ -0,0 +1,11 @@
+# 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
+apport_python_hook.install()
+
+import trio
+
+raise trio.MultiError([KeyError("key_error"), ValueError("value_error")])