[CS2] Enhancement: Support object spread syntax in multiline objects without braces or commas

[laurentpayot]

foo =
  a: 1
  b: 2

bar =
  foo...
  c: 3

results in

error: unexpected ...
	foo...
	   ^^^

For now we have to use:

bar = {
  foo...,
  c: 3
}

It's a bit ugly and it adds an exception to the nice CS way of object notation.

[connec]

Copying #4493 (comment)

---

That's probably related to looksObjectish in the rewriter, which seems to only accept implicit object literals when there's a : involved (which is consistent with being unable to use shorthand properties in implicit objects).

Tbh we probably want to leave it like this, or we'll need to face down ambiguities in expressions like

f k: v, rest...

Which, currently, will compile to two arguments (an object literal and a splat param) but would be ambiguous if we allowed splats to exist in implicit objects.

[connec]

As an aside, commas are still optional, even with explicit braces:

{
  foo...
  bar
  baz: 'qux'
}

[GeoffreyBooth]

I ran into this just writing the documentation. I think it’s a thing that will be very common for people to want to do. Could we find a way to allow spreads in multiline objects, while leaving function arguments unaffected (i.e. to avoid ambiguity problems)?

@helixbass this looks like a rewriter issue, if you feel like taking a crack at it.

[zdenko]

@GeoffreyBooth, @connec, @helixbass
I've started to play with this and made some progress.

foo =
  bar...
  c: 3

compiles to

foo = Object.assign({}, bar, {
    c: 3
  });

f a:x, rest... into f({a:x}, ...rest)

f {a:x, rest...} into

f(Object.assign({
    a: x
  }, rest))

And if I'm correct, there is also this case

foo = 
  bar
  c: 3

which should compile to

foo = {
   bar,
   c: 3
}

[vendethiel]

And if I'm correct, there is also this case

foo = 
  bar
  c: 3

which should compile to

foo = {
   bar,
   c: 3
}

I'm not sure we want this. I read it as foo = bar c: 3 at first, and we don't do that for function calls.

[zdenko]

Current status:

# foo = 
#   bar 
#   c: 3
foo = {
  bar,
  c: 3
}

# foo = 
#   bar c: 3
foo = bar({c:3))

# foo = 
#   bar 
#     c: 3
foo = bar({c:3))

[GeoffreyBooth]

See also #4551 (comment)

[GeoffreyBooth]

Closing per discussion in #4618.