Adding ignoreBOM and fatal to TextDecoder

[Pauan]

Fixes #1729

[alexcrichton]

Looks good to me, thanks!

Could this also include a comment for why the extra options are specified? (in the Rust source, not the generated JS source)

[alexcrichton]

Looks great! I think there are some test failures though?

[Pauan]

@alexcrichton It seems to work fine in Chrome, but is failing in Firefox. I'm investigating it.

[Pauan]

Okay, that took me several hours to debug. It's actually a bug in Firefox:

const decoder = new TextDecoder('utf-8', { ignoreBOM: true, fatal: true });
const slice = new Uint8Array([239, 187, 191, 98, 97, 114]);
console.log(decoder.decode(slice) === decoder.decode(slice));

The above code returns true in Chrome but false in Firefox. Basically, if you use the same TextDecoder multiple times, it ignores the ignoreBOM setting.

This has already been reported and fixed (3 days ago), but it is fixed in Firefox 70, so we have to wait for that to be released.

[alexcrichton]

Nice digging! Want to back out the tests and we can land this anyway for the time being?

[Pauan]

@alexcrichton Done.

[alexcrichton]

👍