Add xeus-cpp kernel (C++20)

[rgbkrk]

Summary

• Adds xeus-cpp to the conformance test suite with C++20 standard (xcpp20 kernel)
• Second of 7 xeus kernels requested in Additional kernels #30

Notes

• Uses xcpp20 since xeus-cling already occupies xcpp17
• xeus-cpp is the modern Clang REPL-based C++ kernel (reboot of xeus-cling)
• Uses existing C++ snippets

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Submitted on @rgbkrk's behalf by his agent Quill

[github-actions]

Kernel Conformance Matrix

Kernel	Protocol	Tier 1	Tier 2	Tier 3	Tier 4	Total
almond	unknown	0/1	0/0	0/0	0/0	0/1
ark	5.4	10/10	5/7	2/3	5/5	22/25
deno	5.3	9/10	6/7	3/3	3/5	21/25
evcxr	5.3	10/10	3/7	1/3	3/5	17/25
gonb	5.4	6/10	1/7	1/3	3/5	11/25
ijulia	5.4	10/10	6/7	2/3	5/5	23/25
ipykernel	5.3	10/10	7/7	3/3	5/5	25/25
xeus-cling	5.3	9/10	4/7	0/3	0/5	13/25
xeus-cpp	5.5	4/10	0/7	0/3	0/5	4/25
xeus-python	5.5	9/10	5/7	3/3	4/5	21/25
xeus-sql	unknown	0/1	0/0	0/0	0/0	0/1

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almond (unknown) - 1 failures, 0 skipped

Language: scala | Protocol: unknown

Failures

Test	Message Type	Likely Source	Reason
kernel_startup	kernel_info_request	protocol_error	Protocol error: missing field date at line 1 column 169

ark () - 3 failures, 0 skipped

Language: R | Protocol: 5.4

Failures

Test	Message Type	Likely Source	Reason
history_request	history_request	unknown	Timeout waiting for shell reply
comm_info_request	comm_info_request	unknown	Timeout waiting for shell reply

deno (Deno kernel) - 3 failures, 1 skipped

Language: typescript | Protocol: 5.3

Failures

Test	Message Type	Likely Source	Reason
interrupt_request	interrupt_request	unknown	Timeout waiting for control reply
shutdown_reply	shutdown_request	unknown	Timeout waiting for control reply

Skipped (Not Implemented)

• stdin_input_request: Kernel can request input from frontend via stdin channel

evcxr (evcxr_jupyter) - 5 failures, 3 skipped

Language: Rust | Protocol: 5.3

Failures

Test	Message Type	Likely Source	Reason
inspect_request	inspect_request	unknown	Timeout waiting for shell reply
history_request	history_request	unknown	Timeout waiting for shell reply
comm_info_request	comm_info_request	unknown	Timeout waiting for shell reply
interrupt_request	interrupt_request	unknown	Protocol error: Error deserializing content for msg_type interrupt_reply: missing field status

Skipped (Not Implemented)

• display_data: Kernel can produce display_data messages for rich output
• update_display_data: Kernel can update existing displays via update_display_data
• stdin_input_request: Kernel can request input from frontend via stdin channel

gonb (gonb) - 14 failures, 0 skipped

Language: go | Protocol: 5.4

Failures

Test	Message Type	Likely Source	Reason
execute_stdout	execute_request	unknown	No stdout containing 'hello'
execute_stderr	stream	unknown	No stderr containing 'error'
execute_reply_ok	execute_request	kernel_error	execute_reply status: Error
complete_request	complete_request	unknown	Timeout waiting for shell reply
inspect_request	inspect_request	unknown	Expected inspect_reply, got "execute_reply"
is_complete_complete	is_complete_request	unknown	Expected is_complete_reply, got "inspect_reply"
is_complete_incomplete	is_complete_request	unknown	Timeout waiting for shell reply
history_request	history_request	unknown	Timeout waiting for shell reply
comm_info_request	comm_info_request	unknown	Timeout waiting for shell reply
execute_result	execute_result	unknown	No execute_result on iopub
stdin_input_request	input_request	unexpected_content	No input_request received on stdin channel
interrupt_request	interrupt_request	unknown	Timeout waiting for control reply
shutdown_reply	shutdown_request	unknown	Timeout waiting for control reply

ijulia (ijulia) - 1 failures, 1 skipped

Language: julia | Protocol: 5.4

Failures

Test	Message Type	Likely Source	Reason
comm_info_request	comm_info_request	unknown	Timeout waiting for shell reply

Skipped (Not Implemented)

• update_display_data: Kernel can update existing displays via update_display_data

xeus-cling (xeus-cling) - 11 failures, 1 skipped

Language: c++ | Protocol: 5.3

Failures

Test	Message Type	Likely Source	Reason
inspect_request	inspect_request	unknown	inspect_reply status: Error
history_request	history_request	unknown	Protocol error: Error deserializing content for msg_type history_reply: data did not match any variant of untagged enum HistoryEntry
comm_info_request	comm_info_request	unknown	Timeout waiting for shell reply
display_data	display_data	unknown	Timeout waiting for iopub idle
update_display_data	update_display_data	unknown	Timeout waiting for iopub idle
execute_result	execute_result	unknown	Protocol error: Codec Error: Broken pipe (os error 32)
comms_lifecycle	comm_open	harness_error	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
interrupt_request	interrupt_request	unknown	Timeout waiting for control reply
execution_count_increments	execute_request	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
parent_header_correlation	parent_header	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
shutdown_reply	shutdown_request	unknown	Protocol error: Codec Error: Broken pipe (os error 32)

Skipped (Not Implemented)

• stdin_input_request: Kernel can request input from frontend via stdin channel

xeus-cpp (xeus-cpp) - 20 failures, 1 skipped

Language: C++ | Protocol: 5.5

Failures

Test	Message Type	Likely Source	Reason
execute_stdout	execute_request	unknown	Timeout waiting for iopub idle
execute_stderr	stream	unknown	Timeout waiting for iopub idle
execute_reply_ok	execute_request	harness_error	Protocol error: Codec Error: Broken pipe (os error 32)
status_busy_idle_lifecycle	status	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
execute_input_broadcast	execute_input	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
complete_request	complete_request	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
inspect_request	inspect_request	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
is_complete_complete	is_complete_request	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
is_complete_incomplete	is_complete_request	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
history_request	history_request	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
comm_info_request	comm_info_request	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
error_handling	execute_request	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
display_data	display_data	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
update_display_data	update_display_data	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
execute_result	execute_result	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
comms_lifecycle	comm_open	harness_error	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
interrupt_request	interrupt_request	unknown	Timeout waiting for control reply
execution_count_increments	execute_request	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
parent_header_correlation	parent_header	unknown	Protocol error: Failed to deliver message (6 frames) cause of Not connected to peers. Unable to send messages
shutdown_reply	shutdown_request	unknown	Protocol error: Codec Error: Broken pipe (os error 32)

Skipped (Not Implemented)

• stdin_input_request: Kernel can request input from frontend via stdin channel

xeus-python (xeus-python) - 4 failures, 0 skipped

Language: python | Protocol: 5.5

Failures

Test	Message Type	Likely Source	Reason
history_request	history_request	unknown	Protocol error: Error deserializing content for msg_type history_reply: data did not match any variant of untagged enum HistoryEntry
comm_info_request	comm_info_request	unknown	Timeout waiting for shell reply
interrupt_request	interrupt_request	unknown	Protocol error: Error deserializing content for msg_type interrupt_reply: invalid type: null, expected struct InterruptReply
shutdown_reply	shutdown_request	unknown	Protocol error: Error deserializing content for msg_type shutdown_reply: invalid type: null, expected struct ShutdownReply

xeus-sql (unknown) - 1 failures, 0 skipped

Language: sqlite | Protocol: unknown

Failures

Test	Message Type	Likely Source	Reason
kernel_startup	kernel_info_request	protocol_error	Protocol error: Error deserializing content for msg_type kernel_info_reply: missing field status

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Test Results by Message Type

Test	Message Type	almond	ark	deno	evcxr	gonb	ijulia	ipykernel	xeus-cling	xeus-cpp	xeus-python	xeus-sql
comm_info_request	comm_info_request	-	❌	✅	❌	❌	❌	✅	❌	❌	❌	-
comms_lifecycle	comm_open	-	✅	✅	✅	✅	✅	✅	❌	❌	✅	-
complete_request	complete_request	-	✅	✅	✅	❌	✅	✅	✅	❌	✅	-
display_data	display_data	-	✅	✅	⏭️	✅	✅	✅	❌	❌	✅	-
error_handling	execute_request	-	✅	✅	✅	✅	✅	✅	✅	❌	✅	-
execute_input_broadcast	execute_input	-	✅	✅	✅	✅	✅	✅	✅	❌	✅	-
execute_reply_ok	execute_request	-	✅	✅	✅	❌	✅	✅	✅	❌	✅	-
execute_result	execute_result	-	✅	✅	✅	❌	✅	✅	❌	❌	✅	-
execute_stderr	stream	-	✅	✅	✅	❌	✅	✅	✅	❌	✅	-
execute_stdout	execute_request	-	✅	✅	✅	❌	✅	✅	✅	❌	✅	-
execution_count_increments	execute_request	-	✅	✅	✅	✅	✅	✅	❌	❌	✅	-
heartbeat_responds	heartbeat	-	✅	✅	✅	✅	✅	✅	✅	✅	✅	-
history_request	history_request	-	❌	✅	❌	❌	✅	✅	❌	❌	❌	-
inspect_request	inspect_request	-	✅	✅	❌	❌	✅	✅	❌	❌	✅	-
interrupt_request	interrupt_request	-	✅	❌	❌	❌	✅	✅	❌	❌	❌	-
is_complete_complete	is_complete_request	-	✅	✅	✅	❌	✅	✅	✅	❌	✅	-
is_complete_incomplete	is_complete_request	-	✅	⚠️	⚠️	❌	✅	✅	✅	❌	✅	-
kernel_info_has_language_info	kernel_info_request	-	✅	✅	✅	✅	✅	✅	✅	✅	✅	-
kernel_info_has_protocol_version	kernel_info_request	-	✅	✅	✅	✅	✅	✅	✅	✅	✅	-
kernel_info_reply_valid	kernel_info_request	-	✅	✅	✅	✅	✅	✅	✅	✅	✅	-
kernel_startup	kernel_info_request	❌	-	-	-	-	-	-	-	-	-	❌
parent_header_correlation	parent_header	-	✅	✅	✅	✅	✅	✅	❌	❌	✅	-
shutdown_reply	shutdown_request	-	✅	❌	✅	❌	✅	✅	❌	❌	❌	-
status_busy_idle_lifecycle	status	-	✅	✅	✅	✅	✅	✅	✅	❌	✅	-
stdin_input_request	input_request	-	✅	⏭️	⏭️	❌	✅	✅	⏭️	⏭️	✅	-
update_display_data	update_display_data	-	⚠️	✅	⏭️	⚠️	⏭️	✅	❌	❌	✅	-