add js.lib.BigInt

[terurou]

BigInt is supported by Chrome, Firefox and Node.js.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt

Node.js v12 was added some BigInt API.
https://nodejs.org/dist/latest-v12.x/docs/api/buffer.html#buffer_buf_readbigint64be_offset

[RealyUniqueName]

This is out of scope of this PR, but if it get merged js.Syntax should probably have a static method, which will instantiate bigint literals because:

A BigInt is created by appending n to the end of an integer literal — 10n — or by calling the function BigInt()

[RealyUniqueName]

I think it should be @:coreType instead of an underlying extern class because BigInt is a primitive type:

BigInt is slated to become the first new primitive type added to JavaScript since Symbol in ES2015.

[RealyUniqueName]

And then all bodies of @:op methods should be removed leaving declarations only. E.g.

@:op(-A) static inline function neg(a:BigInt):BigInt;

[terurou]

I tried to use @:coretype, but it didn't work.
http://try-haxe.mrcdk.com/#091Cf

Haxe converts a++ to a = a + 1. But BigInt + Int doesn't work...

[terurou]

In JS, var a = 1n; a++; works fine.

[RealyUniqueName]

Increment/decrement could still have bodies even with @:coreType

[terurou]

Umm..., increment works fine with untyped __js__, but it doesn't work with Syntax.code().

http://try-haxe.mrcdk.com/#6BB44
http://try-haxe.mrcdk.com/#6B8e6

Is it correct? Should I use untyped __js__?

[RealyUniqueName]

Hm... Yeah, looks like it's the only option for now.

[RealyUniqueName]

@Simn any idea how to make @:op(A++) function():BigInt; not to inline into BigInt(1)++?

[RealyUniqueName]

Are you sure bit shift ops require a BigInt as the right hand argument?

[terurou]

Yes. In V8(Chrome and Node.js),

> 1n << 1
Uncaught TypeError: Cannot mix BigInt and other types, use explicit conversions

But Firefox accepts int.

[terurou]

Oh, I find a mistake of sample code... (It is already fixed.)

It works fine.

> 1n << 1n
2n

It doesn't work.

> 1n << 1
Thrown:
TypeError: Cannot mix BigInt and other types, use explicit conversions

[haxiomic]

@terurou, what do you think about using @:native rather than js.Syntax? The benefit is we'd no longer need to have the if( arg == null ) checks

(same as #8633 (comment))

[terurou]

@haxiomic I tried @:native.
http://try-haxe.mrcdk.com/#B0c66

This is not good... I don't need null.

var a = new BigInt(1);
a.toLocaleString();

BigInt.prototype.toLocaleString.call(BigInt(1),null,null);

[haxiomic]

@terurou thanks for testing, I see what's happening. I guess the null checks are the best approach then

Edit: more discussion #8633 (comment)

[Simn]

What's the status here?

[RealyUniqueName]

This PR still needs some work.
Let's try it for 4.1.

[Simn]

At this point, I suppose it's best to close this particular PR. It would require someone to look into this more, and I don't see that happening.