🐛 Ternaries with parenthesized identifiers as consequents parse as Arrow Function Expressions

[faultyserver]

Environment information

main

What happened?

Playground Link

This is a weirdly specific error that I noticed while trying to test formatting our monorepo for regressions. As shown in the playground, this code fails to parse:

!isDisabled ? (
    foo
  ) : (
    <Tooltip>
      {() => null}
    </Tooltip>
  );

It fails on the arrow function expression inside the JSX expression (the {() => null}). But, this only fails to parse when:

• The consequent of the ternary (the first branch after the ?) is a plain identifier
• The consequent is wrapped in parentheses

After messing around a bit, it looks like what's actually happening here is the parser thinks this is a conditional expression where the consequent is an Arrow Function Expression, rather than treating it as a parenthesized identifier, which is confirmed by looking at the Syntax tab on that playground link as well. Then the JSX in the alternate ends up being parsed as a return type rather than JSX at all, hence the errors that show up here.

It also doesn't matter if the file is parsed as TypeScript or JavaScript, or even with JSX enabled or not. The parse always errors.

As a comparison, ASTExplorer shows that all other JS parsers are able to understand this as a parenthesized identifier rather than starting an arrow expression.

Expected result

Parsing the ternary should succeed as a conditional expression with a parenthesized identifier as the consequent and a JSX expression as the alternate.

Code of Conduct

• I agree to follow Biome's Code of Conduct

[kalleep]

Hey I can take a look at this one if you don't mind

[faultyserver]

@kalleep Sure! I'll assign it to you

[kalleep]

Thanks started to do some digging earlier and pretty sure the issue is from here: https://github.com/biomejs/biome/blob/main/crates/biome_js_parser/src/syntax/function.rs#L587

// error
a ? (b) : (<p>{() => null}</p>);
// error
a ? (b) : <p>{() => null}</p>;

Both of these fails to parse correctly and seems like part of the consequence, up until the arrow, is parsed as typescript return parameter. This results in https://github.com/biomejs/biome/blob/main/crates/biome_js_parser/src/syntax/function.rs#L599 succeeding.

Will keep looking at this tomorrow and work on a fix