Capture correct tracebacks when using inline_callbacks.

[tomprince]

Fixes #449. I'm not sure if this a great solution, but it appears to fix the issue by letting Failure's stack walking find the right context.

When an inlineCallback completes synchronously, such as in tests, twisted will
string-ify the traceback, which means that when the exception is then thrown
into another inlineCallback function, the stack trace is lost[1]. Twisted works
around this by inspect the stack and finding the Failure instance from the
inner call, to get traceback there.

However, this only works if Failure.throwExceptionIntoGenerator is used.
This adjusts eliot_friendly_generator_function to use Failure, instead of an
exc_info tuple, when used via inline_callabcks.

[1] The string-ified traceback can't be passed to .send.

[itamarst]

Thank you! I’m on vacation so will take a look when I return to work.

…

On Wed, Jul 14, 2021, at 4:21 PM, Tom Prince wrote: Fixes #449 <#449>. I'm not sure if this a great solution, but it appears to fix the issue by letting Failure's stack walking find the right context. When an inlineCallback completes synchronously, such as in tests, twisted will string-ify the traceback, which means that when the exception is then thrown into another inlineCallback function, the stack trace is lost[1]. Twisted works around this by inspect the stack and finding the Failure instance from the inner call, to get traceback there. However, this only works if `Failure.throwExceptionIntoGenerator` is used. This adjusts eliot_friendly_generator_function to use `Failure`, instead of an exc_info tuple, when used via `inline_callabcks`. [1] The string-ified traceback can't be passed to `.send`. You can view, comment on, or merge this pull request online at: #475 Commit Summary * Capture correct tracebacks when using `inline_callbacks`. File Changes * *M* eliot/_generators.py <https://github.com/itamarst/eliot/pull/475/files#diff-5fc6644f84f001efb26cd38bfda600a55068805cc22052597de4b961fb7bab98> (13) * *M* eliot/twisted.py <https://github.com/itamarst/eliot/pull/475/files#diff-101a2db4879f60ddd510d70a8f315d1c4906420660b6ba170b01402bb0c7cb6c> (1) Patch Links: * https://github.com/itamarst/eliot/pull/475.patch * https://github.com/itamarst/eliot/pull/475.diff — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#475>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAY5QZREBZMMQVHBZUDAI63TXYLZNANCNFSM5AMMZ56A>.

-- Itamar Turner-Trauring

[itamarst]

Thanks for your patience on a review.

This seems, apriori, fine? If the worry is breaking abstractions, inline callbacks is really the only use case for the generators code, so that seems OK.

So happy to merge this given a test.

[itamarst]

A new version of Twisted has just been released, and at this point the contextvars support in Twisted is probably good enough that normal inlineCallbacks should just work correctly (plus async/await!), with no need for special code in Eliot. If it's still relevant, do you want to try that and see if it works for you?