Check if jupyter-client allows for external kernels

jupyter_server/serverapp.py

@@ -26,6 +26,7 @@
 from base64 import encodebytes
 from pathlib import Path
 
+import jupyter_client
 from jupyter_client.kernelspec import KernelSpecManager
 from jupyter_client.manager import KernelManager
 from jupyter_client.session import Session
@@ -1644,7 +1645,10 @@ def _update_notebook_dir(self, change):
         allow_none=True,
         config=True,
         help=_i18n(
-            "The directory to look at for external kernel connection files, if allow_external_kernels is True. Defaults to Jupyter runtime_dir/external_kernels."
+            "The directory to look at for external kernel connection files, if allow_external_kernels is True. "
+            "Defaults to Jupyter runtime_dir/external_kernels. "
+            "Make sure that this directory is not filled with left-over connection files, "
+            "that could result in unnecessary kernel manager creations."
         ),
     )
 
@@ -1892,20 +1896,25 @@ def init_configurables(self):
             parent=self,
         )
 
-        if self.allow_external_kernels:
-            external_connection_dir = self.external_connection_dir
-            if external_connection_dir is None:
-                external_connection_dir = str(Path(self.runtime_dir) / "external_kernels")
-        else:
-            external_connection_dir = None
+        kwargs = {
+            "parent": self,
+            "log": self.log,
+            "connection_dir": self.runtime_dir,
+            "kernel_spec_manager": self.kernel_spec_manager,
+        }
+        if jupyter_client.version_info > (8, 3, 0):
+            if self.allow_external_kernels:
+                external_connection_dir = self.external_connection_dir
+                if external_connection_dir is None:
+                    external_connection_dir = str(Path(self.runtime_dir) / "external_kernels")
+                kwargs["external_connection_dir"] = external_connection_dir
+        elif self.allow_external_kernels:
+            self.log.warning(
+                "Although allow_external_kernels=True, external kernels are not supported "
+                "because jupyter-client's version does not allow them (should be >8.3.0)."
+            )
 
-        self.kernel_manager = self.kernel_manager_class(
-            parent=self,
-            log=self.log,
-            connection_dir=self.runtime_dir,
-            external_connection_dir=external_connection_dir,
-            kernel_spec_manager=self.kernel_spec_manager,
-        )
+        self.kernel_manager = self.kernel_manager_class(**kwargs)
         self.contents_manager = self.contents_manager_class(
             parent=self,
             log=self.log,

pyproject.toml

@@ -97,9 +97,6 @@ build = "make -C docs html SPHINXOPTS='-W'"
 api = "sphinx-apidoc -o docs/source/api -f -E jupyter_server */terminal jupyter_server/pytest_plugin.py"
 
 [tool.hatch.envs.test]
-pre-install-commands = [
-  "pip install https://github.com/davidbrochart/jupyter_client/archive/external-kernels.zip"
-]
 features = ["test"]
 [tool.hatch.envs.test.scripts]
 test = "python -m pytest -vv {args}"
@@ -112,9 +109,6 @@ dependencies = [ "mypy>=0.990" ]
 test = "mypy --install-types --non-interactive {args:.}"
 
 [tool.hatch.envs.cov]
-pre-install-commands = [
-  "pip install https://github.com/davidbrochart/jupyter_client/archive/external-kernels.zip"
-]
 features = ["test"]
 dependencies = ["coverage[toml]", "pytest-cov"]
 [tool.hatch.envs.cov.scripts]