fix(core): Rethrow caught promise rejections in startSpan, startSpanManual, trace

[Lms24]

This severely messed with my brain today..

Seems like our previous implementation of startSpan et.al. assumed that because we were "cloning" the original promise, unhandled promise rejections would still bubble up to the global onunhandledrejection handler so that Sentry would catch the error.

However, we tried investigating this and found out that our "cloning" mechanism didn't work correctly and because we already added a rejection handler, the promise rejection would not always make it to the global handler.

After adding multiple integration tests, I further narrowed the buggy behaviour down to a rather special case:

async function run() {
  // `await` missing on purpose
  Sentry.startSpan({ name: 'parent_span', op: 'test' }, async () => {
    throw new Error('test error');
  });
 }

 const button = document.getElementById('button1');
 button.addEventListener('click', async () => {
    await run();
});

As we can see in the example, the startSpan call is not awaited which for some reason will lead to the SDK not catching the error. Unless, we apply the fix in this PR.

This PR removes this cloning mechanism in favour of directly attaching a rejection handler to the promise. In this handler, we rethrow the error which should trigger the global handlers.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	75.89 KB (0%)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	67.25 KB (0%)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	60.87 KB (0%)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	31.83 KB (0%)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	30.39 KB (0%)
@sentry/browser - Webpack (gzipped)	22.09 KB (0%)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	73.3 KB (-0.02% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	64.97 KB (-0.02% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	31.12 KB (-0.03% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped)	23.12 KB (-0.05% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	203.77 KB (-0.01% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	93.66 KB (-0.02% 🔽)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	68.58 KB (-0.03% 🔽)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	34.07 KB (-0.04% 🔽)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	67.66 KB (0%)
@sentry/react - Webpack (gzipped)	22.12 KB (0%)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	84.31 KB (0%)
@sentry/nextjs Client - Webpack (gzipped)	48.95 KB (0%)
@sentry-internal/feedback - Webpack (gzipped)	16.6 KB (0%)

[mydea]

Very good find & fix! I think this should be good.