SC9001 internal compiler error: 'ternary must not be void' for an arrow body over two void calls

[ryoppippi]

An arrow function whose body is a conditional expression over two void calls trips an internal compiler error. The diagnostic asks for a report, so here it is.

Repro

export {}
function a(): void {
  console.log('a')
}
function b(): void {
  console.log('b')
}
function main() {
  const flag = process.argv.length > 99
  const pick = (n: number) => (flag ? a() : b())
  pick(1)
}
main()

$ bun void3.ts
b

$ scriptc build void3.ts -o void3
void3.ts:10:32 - error SC9001: internal compiler error: in %fn0: ternary must not be void — please report this

   9 |   const flag = process.argv.length > 99
  10 |   const pick = (n: number) => (flag ? a() : b())
     |                                ^~~~~~~~~~~~~~~~
  11 |   pick(1)

1 error.

Workaround

A block body with if/else compiles and behaves correctly:

const pick = (n: number) => {
  if (flag) a()
  else b()
}

Note

void-returning arrow bodies are documented as supported (SC1090's hint for void in value position says "void-returning arrow bodies compile"), so the conditional form looks like a gap in the same path rather than an intentional refusal.

Encountered while porting a real CLI; the shape was (value) => cond ? emitA(value) : emitB(value) over two functions returning void.

Environment

• scriptc 0.0.17, @scriptc/compiler 0.0.17
• macOS 26.5.2, arm64, Node v24.18.0
• Reproduces on both static and --dynamic builds