Backport PR #12168: Make IPython.core.debugger interruptible by KeyboardInterrupt

docs/source/whatsnew/pr/interruptible-debugger.rst

@@ -0,0 +1,4 b''
+IPython.core.debugger.Pdb is now interruptible
+==============================================
+
+A ``KeyboardInterrupt`` will now interrupt IPython's extended debugger, in order to make Jupyter able to interrupt it.

IPython/core/debugger.py

@@ -634,6 +634,34 b' class Pdb(OldPdb):'
     do_w = do_where
 
 
+class InterruptiblePdb(Pdb):
+    """Version of debugger where KeyboardInterrupt exits the debugger altogether."""
+
+    def cmdloop(self):
+        """Wrap cmdloop() such that KeyboardInterrupt stops the debugger."""
+        try:
+            return OldPdb.cmdloop(self)
+        except KeyboardInterrupt:
+            self.stop_here = lambda frame: False
+            self.do_quit("")
+            sys.settrace(None)
+            self.quitting = False
+            raise
+
+    def _cmdloop(self):
+        while True:
+            try:
+                # keyboard interrupts allow for an easy way to cancel
+                # the current command, so allow them during interactive input
+                self.allow_kbdint = True
+                self.cmdloop()
+                self.allow_kbdint = False
+                break
+            except KeyboardInterrupt:
+                self.message('--KeyboardInterrupt--')
+                raise
+
+
 def set_trace(frame=None):
     """
     Start debugging from `frame`.

IPython/core/tests/test_debugger.py

@@ -4,8 +4,16 b''
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
+import signal
 import sys
+import time
 import warnings
+from tempfile import NamedTemporaryFile
+from subprocess import check_output, CalledProcessError, PIPE
+import subprocess
+from unittest.mock import patch
+import builtins
+import bdb
 
 import nose.tools as nt
 
@@ -223,3 +231,26 b' def can_exit():'
 
     >>> sys.settrace(old_trace)
     '''
+
+
+def test_interruptible_core_debugger():
+    """The debugger can be interrupted.
+
+    The presumption is there is some mechanism that causes a KeyboardInterrupt
+    (this is implemented in ipykernel).  We want to ensure the
+    KeyboardInterrupt cause debugging to cease.
+    """
+    def raising_input(msg="", called=[0]):
+        called[0] += 1
+        if called[0] == 1:
+            raise KeyboardInterrupt()
+        else:
+            raise AssertionError("input() should only be called once!")
+
+    with patch.object(builtins, "input", raising_input):
+        debugger.InterruptiblePdb().set_trace()
+        # The way this test will fail is by set_trace() never exiting,
+        # resulting in a timeout by the test runner. The alternative
+        # implementation would involve a subprocess, but that adds issues with
+        # interrupting subprocesses that are rather complex, so it's simpler
+        # just to do it this way.