make debugger class configurable (#1307)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: smacke

ipykernel/ipkernel.py

@@ -71,6 +71,12 @@ class IPythonKernel(KernelBase):
     shell = Instance("IPython.core.interactiveshell.InteractiveShellABC", allow_none=True)
     shell_class = Type(ZMQInteractiveShell)
 
+    # use fully-qualified name to ensure lazy import and prevent the issue from
+    # https://github.com/ipython/ipykernel/issues/1198
+    debugger_class = Type("ipykernel.debugger.Debugger")
+
+    compiler_class = Type(XCachingCompiler)
+
     use_experimental_completions = Bool(
         True,
         help="Set this flag to False to deactivate the use of experimental IPython completion APIs.",
@@ -110,11 +116,11 @@ def __init__(self, **kwargs):
 
         self.executing_blocking_code_in_main_shell = False
 
-        from .debugger import Debugger, _is_debugpy_available
+        from .debugger import _is_debugpy_available
 
         # Initialize the Debugger
         if _is_debugpy_available:
-            self.debugger = Debugger(
+            self.debugger = self.debugger_class(
                 self.log,
                 self.debugpy_socket,
                 self._publish_debug_event,
@@ -130,7 +136,7 @@ def __init__(self, **kwargs):
             user_module=self.user_module,
             user_ns=self.user_ns,
             kernel=self,
-            compiler_class=XCachingCompiler,
+            compiler_class=self.compiler_class,
         )
         self.shell.displayhook.session = self.session  # type:ignore[attr-defined]