Patch unplugin to pass input source map to transform handlers

[sethfowler-datadog]

What and why?

It looks like cleanly supporting newer versions of rspack will require that we handle source map merging ourselves in the RUM privacy plugin. The underlying instrumentation code already supports this, but we can't take advantage of that, because the Unplugin API doesn't give us access to the input source map. To fix that, this PR patches Unplugin to make the input source map available to transform handlers.

How?

This PR includes a patch (generated using yarn patch) which passes the input source map as a third argument to transform handlers for both webpack and rspack plugins.

(When we upstream this, we should probably do it for all bundlers, but in the short term the focus is on resolving compatibility issues with rspack.)

[datadog-official]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

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[yoannmoinet]

Given our implementation, wouldn't you need to patch both webpack and rspack transforms and loaders?

[sethfowler-datadog]

Given our implementation, wouldn't you need to patch both webpack and rspack transforms and loaders?

I do think we want to do that eventually, but since we're trying to solve a problem with rspack, it seemed to me to make sense to limit the blast radius of the change to rspack until we're sure that the fix is correct and it doesn't introduce any new issues. Happy to revise the patch if you'd prefer to start with webpack as well, though.

[yoannmoinet]

I do think we want to do that eventually, but since we're trying to solve a problem with rspack, it seemed to me to make sense to limit the blast radius of the change to rspack until we're sure that the fix is correct and it doesn't introduce any new issues. Happy to revise the patch if you'd prefer to start with webpack as well, though.

That's fair.