Fix the usage of spreadProps without any other props

[mununki]

// original
let c1 = <A {...p} />

// converted to
// v4 classic
let c1 = React.createElement(A.make, p)

// v4 automatic
let c1 = React.jsx(A.make, p)

[cristianoc]

Shouldn't this be an error?

[mununki]

That would be more nicer, because the second p1 would be ignored anyway.

[mununki]

afdd64b

[cristianoc]

Looking at the generated output, perhaps this should also be the only order allowed, and the first example, in the other order, should be an error?

[mununki]

I think we need to describe the spec of how the spread props will work compared to the js. In js, always the latter one has a priority which means order does matter. But in v4 spread props, independent props always have a priority.

How about allowing reversed order only? The semantic seems matching to the js output.

let c2 = <A {...p} x="x" />

Or, describing on the spec that each independent prop will be updated at the end regardless of order.

[cristianoc]

Exactly. Allowing reverse only seems natural. And avoids confusion if there's only one way.

[mununki]

One thing came to my mind, maybe I think I can extract the (label, expression) list from arguments and label declaration in spread prop. then I can reduce it to the single record expression. I’ll give it a try.

[mununki]

Ah..I confused. Never mind the reduce thing, p is a just Lident not Pexp_record.

[mununki]

afdd64b

[cristianoc]

This is great.
Just added a couple of suggestions to make the error message easier to understand.
Other than that, ready to go.