Error message patterns prevent Firefox from improving messages

[miketaylr]

Over in Bug 1498257, we've had to back out some DX improvements to error messages from Firefox's JS engine because it broke Flipkart (the number 6 site in India, top 150 globally).

It turns out the reason is idx, see https://bugzilla.mozilla.org/show_bug.cgi?id=1498257#c7 for more details.

https://github.com/facebookincubator/idx/blob/master/packages/idx/src/idx.js#L73-L84

I'm not sure how widely this lib is used, but fixing here would allow us to attempt error message improvements again.

https://hg.mozilla.org/integration/mozilla-inbound/rev/f0c6e521429c is the changeset that was backed out. Some example improved error messages are:

TypeError: win.browser.runtime is undefined, can't access property "getManifest" of it
TypeError: [...][Symbol.iterator](...).next(...).value is null, can't access property Symbol.iterator of it

[yungsters]

In retrospect, I should never have implemented a runtime counterpart to idx (if even just for demonstration). It has enabled too many people to use it without the babel-plugin-idx. 👎

I'm sorry that this has prevented you from making progress. For now, the fastest path forward will probably be to add support for your new error messages here: https://github.com/facebookincubator/idx/blob/master/packages/idx/src/idx.js#L62

But if you have someone who you're working with at Flipkart, we should strongly encourage them to adopt babel-plugin-idx (which might also improve their runtime performance).

[davidben]

Perhaps idx could wrap its first argument in a Proxy that does the undefined check on lookup, returning rewrapped values to keep going. Then you call the user-supplied function, and unwrap the result to return.

You may need to feature-detect support and fallback to error regexes, but it should leave newer browsers unconstrained.

[yungsters]

Either suggestion seems fine to me. I would even be fine with changing idx to throw an error message stating that babel-plugin-idx has not been enabled.

But I probably won't be able to improve the polyfill anytime soon. I can help review pull requests, though.

[yungsters]

@miketaylr, were you able to resolve the matter with Flipkart by using babel-plugin-idx?

[yungsters]

Closing this out due to inactivity.

Feel free to open a new issue if you or anyone would like to revive the discussion about doing away with the runtime implementation.