Updates analytics error handling to support checking delivery failures on Context

[chrisradek]

This PR attempts to standardize how plugin errors impact analytics API calls and provides a straightforward way to check if event delivery failed.

Background

Errors in enrichment, destination, and after plugins don't cause analytics calls to throw. before plugins do, but what they throw depends on if retries are enabled or not. If there are no retries, their errors bubble up to the analytics call. If there are retries, the event's Context itself gets thrown.
To further complicate things, source middleware (implemented as a before plugin) does not bubble errors if next is never called, but does otherwise.

Only before plugins and source middleware errors can cause event delivery to fail entirely, but the inconsistent behavior makes it difficult to write code that can react to these failures.

Changes

The following has been changed:

• all plugins now act consistently in that errors are no longer bubbled up to the analytics calling code (e.g. analytics.track())
• before plugins now support cancelation: this is a bug fix, existing test missed that this was broken
• Context.failedDelivery() is added, so now the following works:

  const context = await analytics.track('event');
  if (context.failedDelivery()) {
    // log failure, retry, etc
  }

This also has the benefit that callbacks can now be invoked even on failures, so you can do:

analytics.track('event', (context) => {
  if (context.failedDelivery()) {
    // log failure, retry, etc
  }
})

Previously callbacks weren't being invoked if the analytics call threw.

Chore

Also updated the vscode launch.json so the actions work in packages/browser.

[pooyaj]

amazing 🙌

[chrisradek]

Just realized I missed one scenario - before plugin fails the 1st time then succeeds on retry. Will need to update the context in this case so that context.getFailedDelivery() does not return anything.

[changeset-bot]

🦋 Changeset detected

Latest commit: 62e445e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@segment/analytics-next	Minor

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