mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-11-03 07:54:40 +08:00
Chris Tate
aeb429c066
- An empty `[]` whose own type is `never[]` (a `return []` in an async function, whose contextual type is `T[] | PromiseLike<T[]>`, or an object literal's `files: []` field) builds as the unit-only element array, like the empty tuple, so typed array slots receive it through the checked empty-array lift. It was `number[]`, so `string[]` slots refused it with SC1090 or SC2002. - The refusal "instanceof against this native constructor" names its site, and coverage lists the sites whose right-hand side is `Object` or `Function`, which always reach it. An arrow function or method on the right of an untyped `instanceof` throws Node's "Function has non-object prototype" TypeError for an object. - Coverage lists the diagnostics of a function whose signature did not compile. A use of a parameter whose type did not compile reports SC2004. - Coverage lists deferred fences in a module's top-level code under "runs at startup", and the diagnostics envelope marks them `startup: true`.
59 lines
1.5 KiB
TypeScript
59 lines
1.5 KiB
TypeScript
// Empty array literals whose own type is `never[]`: `return []` in an async
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// function (its contextual type is `string[] | PromiseLike<string[]>`) and
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// an object literal's `files: []` field returned or passed where typed
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// arrays are declared. Each value holds the declared element type.
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interface Listing {
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files: string[];
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sizes: number[];
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}
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async function readNames(text: string): Promise<string[]> {
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try {
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return JSON.parse(text) as string[];
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} catch {
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return [];
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}
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}
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const loadIds = async (fail: boolean): Promise<number[]> => {
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if (fail) return [];
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return [1, 2];
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};
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function emptyListing(): Listing {
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const listing = { files: [], sizes: [] };
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return listing;
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}
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function index(): Record<"files" | "dirs", string[]> {
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const out = { files: [], dirs: [] };
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return out;
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}
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function total(listing: Listing): number {
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return listing.sizes.reduce((sum, size) => sum + size, 0);
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}
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async function main(): Promise<void> {
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const names = await readNames("not json");
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names.push("fallback");
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console.log(names, (await readNames('["a","b"]')).join("+"));
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const ids = await loadIds(true);
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ids.push(7);
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console.log(ids, await loadIds(false));
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const listing = emptyListing();
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listing.files.push("a.txt");
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listing.sizes.push(3, 4);
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console.log(listing, total(listing));
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const dirs = index();
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dirs.dirs.push("src");
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console.log(JSON.stringify(dirs), dirs.files.length);
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const blank = { files: [], sizes: [] };
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console.log(total(blank), JSON.stringify(blank));
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}
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main();
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