static: an object-literal key named arguments inside an arrow function is read as the arguments object (SC2009) #431

Summary

Inside an arrow function, an object-literal property named arguments is treated as a read of the arguments object. The function is then refused as variadic (SC2009). Node's own APIs have this shape: node-redis takes { keys, arguments } in eval/evalSha.

Reproduction

const make = (): { arguments: number } => ({ arguments: 1 })
console.log(make().arguments)

$ node a.ts
1
$ scriptc run a.ts
a.ts:1:7 - error SC2009: values of type '() => { arguments: number; }' cannot be compiled: the function shape is supported, but its signature is variadic ('arguments'-reading), and a compiled signature is fixed-arity

The same body in a function declaration compiles. So does a property access such as o.arguments.

A more realistic form:

interface Options { keys: string[]; arguments: string[] }
const count = (options: Options): number => options.keys.length + options.arguments.length
const later = (): number => count({ keys: ['a'], arguments: ['b', 'c'] })
console.log(later()) // Node: 3; scriptc: SC2009 on `later`

Cause

bodyReadsArguments (frontend/lowering/lower-calls.ts) and its copy bodyReadsArgumentsLocal (frontend/type-mapper.ts) count every Identifier whose text is arguments, except the name of a property access. A property-assignment name in an object literal is also an Identifier, so it counts. So would a property signature in an inline type, a destructuring property name (const { arguments: a } = o) or a method name.

Writing the key as ['arguments'] avoids it.

Environment

scriptc 0.1.4, Ubuntu 26.04 x86_64, Node 24.21.0.