[sqlite3] the trace callback does not raise exceptions on error

[erlend-aasland]

BPO	45089
Nosy	@encukou, @ambv, @pablogsal, @miss-islington, @erlend-aasland
PRs	bpo-45089: raise exceptions on error in sqlite3 trace callback #28133 bpo-45089: Improve sqlite3 trace callback docs #28238 [3.10] bpo-45089: Improve sqlite3 trace callback docs (GH-28238) #28371 [3.9] bpo-45089: Improve sqlite3 trace callback docs (GH-28238) #28372
Files	reproducer.py

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-09-15.19:12:27.807>
created_at = <Date 2021-09-02.20:42:25.993>
labels = ['extension-modules', '3.11', 'docs']
title = '[sqlite3] the trace callback does not raise exceptions on error'
updated_at = <Date 2021-10-04.20:48:21.288>
user = 'https://github.com/erlend-aasland'

bugs.python.org fields:

activity = <Date 2021-10-04.20:48:21.288>
actor = 'erlendaasland'
assignee = 'docs@python'
closed = True
closed_date = <Date 2021-09-15.19:12:27.807>
closer = 'lukasz.langa'
components = ['Documentation', 'Extension Modules']
creation = <Date 2021-09-02.20:42:25.993>
creator = 'erlendaasland'
dependencies = []
files = ['50259']
hgrepos = []
issue_num = 45089
keywords = ['patch']
message_count = 9.0
messages = ['400955', '401283', '401353', '401354', '401880', '401885', '401887', '401888', '403179']
nosy_count = 6.0
nosy_names = ['petr.viktorin', 'docs@python', 'lukasz.langa', 'pablogsal', 'miss-islington', 'erlendaasland']
pr_nums = ['28133', '28238', '28371', '28372']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue45089'
versions = ['Python 3.11']

[erlend-aasland]

Currently, two calls can raise exceptions in the _trace_callback() in Modules/_sqlite/connection.c:

1. PyUnicode_DecodeUTF8() can raise an exception
2. PyObject_CallOneArg() — calling the user callback — can raise an exception

Currently, we either PyErr_Print() the traceback, or we PyErr_Clear() it. In either case; we clear the current exception. The other SQLite callbacks pass some kind of return value back to SQLite to indicate failure (which is normally then passed to _pysqlite_seterror() via sqlite3_step() or sqlite3_finalize(), but the trace callback does not pass errors back to SQLite; we're unable to detect if the trace callback fails.

[erlend-aasland]

Quoting Petr from PR 28133:
Without the ability to tell SQLite to abort on trace failure, I doubt we can
do much better than the current behavior. Getting an exception and having
the data inserted seems quite irregular.

Closing this issue as won't fix.

[encukou]

It *would* be possible to improve the documentation, though.
Say that it is only meant for debugging, document that exceptions are not propagated, and mention enable_callback_tracebacks.