mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-11-01 07:33:12 +08:00
Malte UblandClaude Opus 5.5
677710075a
`''.match(re) ?? []` typed the literal uninhabited (`never[]`), whose element still mapped through never's f64 value representation, so the whole expression was `RegExpMatchArray | number[]` — a result no single array slot can receive. A union return such as `"all" | readonly string[]` refused with SC2003 "union conversion has no unambiguous layout mapping" (`getScriptReach` in a coding agent's tool-discovery path). An EMPTY array-literal default has no element of its own: it adopts the left's present array arm, exactly the rule the union slot and the ternary arm already state for an empty literal. The left's nullish test and the lazy default are unchanged, and a default whose own type already matches the left keeps the identical lowering it had. Corpus: tests/corpus/nullish-empty-array-default.ts pins the union return, string element reads through the default, the declared optional-array slot with a fresh empty value per evaluation, and a parenthesized/template default. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
41 lines
1.8 KiB
TypeScript
41 lines
1.8 KiB
TypeScript
// `''.match(re) ?? []`: the empty array-literal default of a `??` adopts the
|
|
// left's present array arm. tsc gives the literal the uninhabited `never[]`
|
|
// element, which the compiler maps through never's f64 value representation
|
|
// (`number[]`), so the whole expression used to be `RegExpMatchArray |
|
|
// number[]` — a result no single array slot can receive.
|
|
|
|
// A union return (`"all" | readonly string[]`) whose array arm is the
|
|
// `?? []` result.
|
|
function reach(code: unknown): "all" | readonly string[] {
|
|
if (typeof code !== "string") return [];
|
|
return /\bALL\b/.test(code) ? "all" : (code.match(/\w+/g) ?? []);
|
|
}
|
|
console.log(JSON.stringify(reach(7)));
|
|
console.log(JSON.stringify(reach("ALL")));
|
|
console.log(JSON.stringify(reach("a.b c")));
|
|
console.log(JSON.stringify(reach("")));
|
|
|
|
// The default's element type is the left's: string element reads and a
|
|
// map callback over the value compile as strings, and an absent match
|
|
// answers the empty array Node does.
|
|
const names = "a-b c".match(/[a-z]+/g) ?? [];
|
|
console.log(names.map((name) => name.toUpperCase()).join("+"));
|
|
const none = "123".match(/[a-z]+/g) ?? [];
|
|
console.log(none.length, JSON.stringify(none), names.length);
|
|
|
|
// A declared optional array keeps its own type through the same default,
|
|
// and the fresh empty array is a value of its own (mutation, identity).
|
|
function fill(source: number[] | undefined, with_: number): number[] {
|
|
const list = source ?? [];
|
|
list.push(with_);
|
|
return list;
|
|
}
|
|
console.log(JSON.stringify(fill(undefined, 1)), JSON.stringify(fill([7, 8], 9)));
|
|
const first = fill(undefined, 2);
|
|
const second = fill(undefined, 3);
|
|
console.log(first !== second, JSON.stringify(first), JSON.stringify(second));
|
|
|
|
// A parenthesized default and one inside a longer expression.
|
|
const longest = ("abbbc".match(/b+/g) ?? []).length;
|
|
console.log(longest, `${JSON.stringify("xyz".match(/q/g) ?? [])}!`);
|