Right now there are only two ways to use a ZoneSpecification to interact with exceptions: [handleUncaughtError], which is passed the error when it would leave the zone; and [registerCallback] et al, which can wrap the callback in a try/catch block to capture exceptions that are raised.
I'm trying to implement a solution to issue #7040 using zones (as suggested on that bug), and I'm finding that these two methods of interacting with exceptions aren't sufficient. When tracking the stack traces that are relevant to a given exception, it's important to know the context at the exact point in time the exception is signaled. We can do this to some extent using [registerCallback] and try/catch, but this provides no visibility into exceptions reported using e.g. [Completer.completeError].
Here's a straw-man proposal: ZoneSpecification.registerErrorHandler takes the same arguments as HandleUncaughtErrorHandler and returns something like the internal _AsyncError type -- an error/stack-trace pair. It's called whenever an exception reaches dart:async, either by being thrown or passed explicitly using [Completer.completeError] or similar. The return value is used as the error that's saved and propagated, or passed to [handleUncaughtError].
In addition to supporting issue #7040, this would make it easy to e.g. write code to detect places where errors are thrown without stack traces, or even to automatically add stack traces.
Right now there are only two ways to use a ZoneSpecification to interact with exceptions: [handleUncaughtError], which is passed the error when it would leave the zone; and [registerCallback] et al, which can wrap the callback in a try/catch block to capture exceptions that are raised.
I'm trying to implement a solution to issue #7040 using zones (as suggested on that bug), and I'm finding that these two methods of interacting with exceptions aren't sufficient. When tracking the stack traces that are relevant to a given exception, it's important to know the context at the exact point in time the exception is signaled. We can do this to some extent using [registerCallback] and try/catch, but this provides no visibility into exceptions reported using e.g. [Completer.completeError].
Here's a straw-man proposal: ZoneSpecification.registerErrorHandler takes the same arguments as HandleUncaughtErrorHandler and returns something like the internal _AsyncError type -- an error/stack-trace pair. It's called whenever an exception reaches dart:async, either by being thrown or passed explicitly using [Completer.completeError] or similar. The return value is used as the error that's saved and propagated, or passed to [handleUncaughtError].
In addition to supporting issue #7040, this would make it easy to e.g. write code to detect places where errors are thrown without stack traces, or even to automatically add stack traces.