Remove support of children spread inside JSX

[Copilot]

This PR removes support for JSX children spread syntax while preserving props spread functionality.

What was removed

Children spread syntax like this is no longer supported:

<div> ...children </div>
<Component> ...rest </Component>
<> ...items </>

What still works

Props spread continues to work as before:

<Button {...buttonProps} />
<div className="wrapper" {...divProps} />
<MyComponent id="test" {...rest} onClick={handler} />

Normal JSX children also continue to work:

<div> {text} {otherElement} </div>
<Container> <span>child</span> </Container>

Implementation details

The changes remove the JSXChildrenSpreading variant from the jsx_children type and update all related code:

• Parser: Updated parse_jsx_children to no longer recognize ... syntax in children context
• Type system: Removed JSXChildrenSpreading of expression from jsx_children type
• Processing: Updated all AST mappers, iterators, printers, and analysis tools
• Tests: Removed children spread examples from test files

The implementation is minimal and surgical - only the children spread functionality is removed while all other JSX features remain unchanged.

Files changed

• Core type definition in parsetree.ml
• Parser logic in res_core.ml and printer in res_printer.ml
• AST processing across 8 files in compiler/ml/
• Syntax processing in 3 files in compiler/syntax/src/
• Frontend and analysis support files
• Test cases updated to remove children spread examples

This change makes the JSX syntax more consistent by having spread syntax only available in props context.

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commit: 605b78d

[nojaf]

Looks good at a glance. Can we add a test to check which parsing error we now get for ...? If that’s too cryptic, I’d raise a custom parser error that clearly states child spreading was removed.

[zth]

This can be removed now as well, right? Should probably do that in the same PR.

[tsnobip]

fixed!

[tsnobip]

Looks good at a glance. Can we add a test to check which parsing error we now get for ...? If that’s too cryptic, I’d raise a custom parser error that clearly states child spreading was removed.

@nojaf that's a good point, unfortunately the error is indeed quite cryptic!

  Syntax error!
  syntax_tests/data/parsing/errors/expressions/jsx.res:18:15-17

  16 │ 
  17 │ // spread children
  18 │ let x = <div> ...c </div>

  Did you forget a `</` here?


  Syntax error!
  syntax_tests/data/parsing/errors/expressions/jsx.res:18:15-17

  16 │ 
  17 │ // spread children
  18 │ let x = <div> ...c </div>

  I'm not sure what to parse here when looking at "...".


  Syntax error!
  syntax_tests/data/parsing/errors/expressions/jsx.res:18:22-25

  16 │ 
  17 │ // spread children
  18 │ let x = <div> ...c </div>

  unterminated regex

[nojaf]

@tsnobip inside the loop you probably want to match ... and give a better parse error.

[tsnobip]

@nojaf is it better like that?

[nojaf]

Yes, does wrapping it {...c} do anything?
Syntax-wise probably that is going to be valid.
Would surprise me if that type-checks though.

[nojaf]

Great work!