Stacktraces for Swift Concurrency

[kabiroberai]

Platform

iOS

Installed

Swift Package Manager

Version

7.16.0

Steps to Reproduce

1. Create an async function, with a suspension point (such as await Task.sleep(…))
2. Capture a Sentry event after the suspension point

It should be possible to repro this with the sample introduced in #1504

Expected Result

The Sentry dashboard shows the entire stack trace, including the async function’s caller

Actual Result

The stack trace stops at the function inside which the error was logged, showing the caller as swift::runJobInEstablishedExecutorContext

Sentry would ideally stitch together parent Task stack frames, similar to how stitchAsyncCode from #998 works for libdispatch.

[kabiroberai]

What the stack trace currently looks like:

[brustolin]

Hey @kabiroberai Thanks for your input. It would be awesome to have the stacktrace stitch, right now we don't have an ETA for this.

[philipphofmann]

As pointed out by @brustolin, we have an experimental feature for this @kabiroberai. You can enable stitchAsyncCode and let us know what you think.

sentry-cocoa/Sources/Sentry/Public/SentryOptions.h

Lines 144 to 152 in 17a7a28

	/**
	* Attention: This is an experimental feature. Turning this feature on can have an impact on
	* the grouping of your issues.
	*
	* When enabled, the SDK stitches stack traces of asynchronous code together.
	*
	* This feature is disabled by default.
	*/
	@property (nonatomic, assign) BOOL stitchAsyncCode;

[philipphofmann]

I created an issue for pointing that out in the docs and the wizard getsentry/sentry-docs#5215.

[kabiroberai]

If I understand correctly, stitchAsyncCode is specifically for GCD; it doesn't work with Swift Concurrency task stack frames, which require special handling. To see what I mean, check out how Swift's reflection libs handle it at https://github.com/apple/swift/blob/d52dddc7c8448fc9529463bdeb32fbf6b221b5a6/include/swift/Reflection/ReflectionContext.h#L1687-L1699 (the pointer to the current task is stored in thread-local variable 103 on Darwin; there's a ton of other info in there that may be useful for Sentry too!)

[kabiroberai]

Also worth mentioning Darwin's backtrace_async which is like backtrace(3) but with async stack frames included. Here's the source in Apple's libc: https://github.com/apple-oss-distributions/Libc/blob/dbde50970329ace8793fca2b63d708d280c33d88/gen/backtrace.c#L47

[philipphofmann]

Thanks for pointing that out, @kabiroberai. Yes, the solution should be similar to stitchAsyncCode for GCD.