Support for preconditionFailure message

[mattyohe]

Calls to Swift's preconditionFailure (and likely its friends assertionFailure, fatalError etc) that occur in 5.6.5 do not appear to bubble up the message parameter for reporting in the stack trace that is viewable on Bugsnag.com.

It is unclear to me if this is a deficiency in Bugsnag or Swift.

Example:
Calling the code below in an application that uses Bugsnag:

public var name: String {
  preconditionFailure("Example of an error")
}

Would produce a trace similar to:

0  MyApp               name.get (MyApp.swift:10:20)

But the message "Example of an error" would not be reported.

[kattrali]

Interesting. Thanks for the report, @mattyohe. I'll look into it 🕵️‍♀️

[kattrali]

It looks like there's no message because the provided text isn't attached to the exception in some way, and is only printed. preconditionFailure, fatalError, et cetera call _assertionFailure, which prints the message using _swift_stdlib_reportFatalErrorInFile before terminating execution using Builtin.int_trap().

For now, I don't see how we can support this, but its something to revisit in the future and potentially discuss on the mailing list, as I think we can make the function arguments more accessible.

[edenman]

Is there a different method we should call instead of fatalError to get the message to propagate on a forced crash?

[edenman]

Also FWIW the Sentry guys seem to have figured out how to extract the message: https://github.com/getsentry/sentry-cocoa/pull/188/files