When errors occur in display formatting, the traceback is displayed as error but `execute_reply` is marked as success

[krassowski]

Description

When an error occurs during display formatting, the traceback is displayed as error but execute_reply is marked as success.

Based on discussion in:

• IPython magic UsageErrors do not set status:error on execute_reply #143
• Simplify detection of errors for execute_reply messages #152

I suspect that this might have been lost in ipykernel unintentionally in or following #152. Since that PR did not include tests and removed exc_content[u'status'] = u'error' from _showtraceback replacing it with unified error handling, I think that either it or a subsequent regression in unified error handling made the traceback no longer mark execution as failed.

ipykernel/ipykernel/zmqshell.py

Lines 666 to 690 in 2818b66

	def _showtraceback(self, etype, evalue, stb):
	# try to preserve ordering of tracebacks and print statements
	sys.stdout.flush()
	sys.stderr.flush()
	exc_content = {
	"traceback": stb,
	"ename": str(etype.__name__),
	"evalue": str(evalue),
	}
	dh = self.displayhook
	# Send exception info over pub socket for other clients than the caller
	# to pick up
	topic = None
	if dh.topic: # type:ignore[attr-defined]
	topic = dh.topic.replace(b"execute_result", b"error") # type:ignore[attr-defined]
	dh.session.send( # type:ignore[attr-defined]
	dh.pub_socket, # type:ignore[attr-defined]
	"error",
	json_clean(exc_content),
	dh.parent_header, # type:ignore[attr-defined]
	ident=topic,
	)

_showtraceback is relevant because in IPython formatters are decorated by @catch_format_error which displays any exception caught during the formatting routine using ip.showtraceback() delegated in subclasses - such as ipykernel's to _showtraceback().

Reproduce

Execute:

1/0

See status "error"

Then execute:

class Test:
    def __repr__(self):
        1 / 0

Test()

See status "ok":

Context

Noticed in:

• No notification on exception raised in __repr__ method (and similar) deshaw/jupyterlab-notify#32