Debugging parcel build vs parcel serve issues?

[jaredkrinke]

I've been using Parcel on a project for a few years, but recently my parcel build production builds stopped working (at run-time, not build-time), while parcel serve works flawlessly.

Does anyone have tips on how to debug issues that only show up with parcel build but not parcel serve?

I've tried:

• Disabling optimization (has no obvious effect)
• Disabling scope hoisting (causes new errors I'm still investigating)

I cranked up the log level and it's logging "Conditional or non-top-level require() call" a lot, which I think might be preventing scope hoisting, but I don't think these should prevent the build from working correctly. I suspect this issue is related to TypeScript configuration because it's literally flagging a top-level import as not top-level. But again, I don't think that should prevent anything from working.

Specific error info

The error I'm seeing is:

ReferenceError: $e21355414fd2bd2a$exports is not defined

And indeed if I search for $e21355414fd2bd2a$exports in my produced index.js, that variable is referenced here:

var t, n = (oc(t = $e21355414fd2bd2a$exports.useContext(os)),

But it's never defined or referenced anywhere else. I think Parcel generates this code, but I'm not sure how it's supposed to work yet.

For what it's worth, I've tracked down the precise change in my code that triggers my issue, but all I'm doing is using an imported component in a new file--something I've been doing all over the place without issue for years now. My best guess is that the issue is related to some ordering in the resulting index.js, but that's just a guess for now.

[jaredkrinke]

I got lucky with a random shot in the dark:

My app was originally built around Preact, and everything worked fine. I recently started using react-intl, and (after I got it setup correctly) everything worked fine for parcel serve, but any use of react-intl's <FormattedMessage> would trigger the previously noted exception at run-time in the web app built with parcel build.

As an experiment, I switched from Preact to React and... the issue went away.

To summarize: Parcel+Preact+react-intl didn't work but Parcel+React+react-intl does work, but I have no idea why. I'm not sure if it's a Preact or Parcel issue--my guess would be Parcel, but I have no idea. In the future, I'll try and create a trivial repro and open an issue.