Description

GuzzleHttp\Client::transfer() can throw synchronously before returning a
promise — e.g. when invalid request options are supplied, since applyOptions()
runs outside transfer()'s try/catch. In that case the extension invokes the
transfer post hook with a null return value.

The post hook typed the promise as non-nullable (PromiseInterface $promise), so
the runtime signature check failed: the hook was skipped, the span leaked (never
ended/detached), and an E_CORE_WARNING was emitted:

GuzzleHttp\Client::transfer(): OpenTelemetry: post hook invalid signature,
class=GuzzleHttp\Client function=transfer

This surfaces as a fatal error in error trackers such as Sentry.

Fix

• Make the post hook's promise parameter nullable (?PromiseInterface $promise).
• When the promise is null (synchronous throw), end the span — unless it was
  already ended via the exception branch — and return instead of dereferencing
  null.

Test

Adds a regression test that triggers a synchronous throw via a numerically-indexed
headers option and asserts the span is still ended with an error status.

Related

Same class of "post hook invalid signature / span leak on throw" issue previously
fixed for other instrumentations:

• auto-curl: Fix post hook exception possibility in opentelemetry-auto-curl #335 (issue [opentelemetry-php-contrib] post hook exception in opentelemetry-auto-curl opentelemetry-php#1531)
• Symfony Messenger: fix: post hook invalid when symfony messenger sender throws exception #267