Add causal chain to the stack string

[cstorey-monzo]

I've been chasing down a bunch of errors in tests where (*terrors.Error).StackString() was empty, which isn't convenient, so I've added the causal chain into the stack trace. Without this, even a single usage of terrors.Augment() would mean that stack traces would be blank (this might be why I've seen a bunch of blank stacktraces in Kibana, too).

[alinbalutoiu]

Do you mind adding some comments here or updating the function comment?

[alinbalutoiu]

Also, do you think we need to worry about the performance here if we have a really long call stack? 🤔

[cstorey-monzo]

I wasn't quite sure what you were going for with the comments, so I've just followed the inferred intent of the original.

And for performance; granted, there is a risk of poor performance in extreme circumstances. But on the other hand, I feel like the usage of strings.Buffer over repeated use of fmt.Sprintf() is enough of a net win to outweigh any downside in most circumstances.

[franzbecker]

Just asking:

❓ Will this yield to new duplicate Sentry issues (if changing the stack trace)?

[cstorey-monzo]

Will this yield to new duplicate Sentry issues (if changing the stack trace)?

Possibly. I'll try to remember to post a quick heads-up in #backend-announcements, or similar.

[cstorey-monzo]

For the record, I don't think it will have any impact on sentry reports.