Deprecate Comm class + Fix incompatibility with ipywidgets (#1097)Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

* Deprecate Comm class

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix tests

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix comm creation

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Don't fail on warnings mismatch for ipywidgets downstream tests

* Escape

* Disable more deprecation tests in ipywidgets tests

---------

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

Author: martinRenou

.github/workflows/downstream.yml

@@ -38,6 +38,7 @@ jobs:
         uses: jupyterlab/maintainer-tools/.github/actions/downstream-test@v1
         with:
           package_name: ipywidgets
+          test_command: pytest -vv -raXxs -k \"not deprecation_fa_icons and not tooltip_deprecation and not on_submit_deprecation\" -W default --durations 10 --color=yes
 
   jupyter_client:
     runs-on: ubuntu-latest

ipykernel/comm/comm.py

@@ -5,6 +5,7 @@
 
 import uuid
 from typing import Optional
+from warnings import warn
 
 import comm.base_comm
 import traitlets.config
@@ -70,8 +71,17 @@ def _default_kernel(self):
     def _default_comm_id(self):
         return uuid.uuid4().hex
 
-    def __init__(self, target_name='', data=None, metadata=None, buffers=None, **kwargs):
+    def __init__(
+        self, target_name='', data=None, metadata=None, buffers=None, show_warning=True, **kwargs
+    ):
         """Initialize a comm."""
+        if show_warning:
+            warn(
+                "The `ipykernel.comm.Comm` class has been deprecated. Please use the `comm` module instead."
+                "For creating comms, use the function `from comm import create_comm`.",
+                DeprecationWarning,
+            )
+
         # Handle differing arguments between base classes.
         had_kernel = 'kernel' in kwargs
         kernel = kwargs.pop('kernel', None)

ipykernel/comm/manager.py

@@ -3,11 +3,16 @@
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
+import logging
 
 import comm.base_comm
 import traitlets
 import traitlets.config
 
+from .comm import Comm
+
+logger = logging.getLogger("ipykernel.comm")
+
 
 class CommManager(comm.base_comm.CommManager, traitlets.config.LoggingConfigurable):
     """A comm manager."""
@@ -21,3 +26,37 @@ def __init__(self, **kwargs):
         # CommManager doesn't take arguments, so we explicitly forward arguments
         comm.base_comm.CommManager.__init__(self)
         traitlets.config.LoggingConfigurable.__init__(self, **kwargs)
+
+    def comm_open(self, stream, ident, msg):
+        """Handler for comm_open messages"""
+        # This is for backward compatibility, the comm_open creates a a new ipykernel.comm.Comm
+        # but we should let the base class create the comm with comm.create_comm in a major release
+        content = msg["content"]
+        comm_id = content["comm_id"]
+        target_name = content["target_name"]
+        f = self.targets.get(target_name, None)
+        comm = Comm(
+            comm_id=comm_id,
+            primary=False,
+            target_name=target_name,
+            show_warning=False,
+        )
+        self.register_comm(comm)
+        if f is None:
+            logger.error("No such comm target registered: %s", target_name)
+        else:
+            try:
+                f(comm, msg)
+                return
+            except Exception:
+                logger.error("Exception opening comm with target: %s", target_name, exc_info=True)
+
+        # Failure.
+        try:
+            comm.close()
+        except Exception:
+            logger.error(
+                """Could not close comm during `comm_open` failure
+                clean-up.  The comm may not have been opened yet.""",
+                exc_info=True,
+            )

ipykernel/tests/test_comm.py

@@ -1,5 +1,7 @@
 import unittest.mock
 
+import pytest
+
 from ipykernel.comm import Comm, CommManager
 from ipykernel.ipkernel import IPythonKernel
 from ipykernel.kernelbase import Kernel
@@ -9,7 +11,8 @@ def test_comm(kernel: Kernel) -> None:
     manager = CommManager(kernel=kernel)
     kernel.comm_manager = manager  # type:ignore
 
-    c = Comm(kernel=kernel, target_name="bar")
+    with pytest.deprecated_call():
+        c = Comm(kernel=kernel, target_name="bar")
     msgs = []
 
     assert kernel is c.kernel  # type:ignore
@@ -53,7 +56,8 @@ def on_msg(msg):
 
     kernel.comm_manager = manager  # type:ignore
     with unittest.mock.patch.object(Comm, "publish_msg") as publish_msg:
-        comm = Comm()
+        with pytest.deprecated_call():
+            comm = Comm()
         comm.on_msg(on_msg)
         comm.on_close(on_close)
         manager.register_comm(comm)
@@ -96,5 +100,7 @@ def on_msg(msg):
 
 
 def test_comm_in_manager(ipkernel: IPythonKernel) -> None:
-    comm = Comm()
+    with pytest.deprecated_call():
+        comm = Comm()
+
     assert comm.comm_id in ipkernel.comm_manager.comms