mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-11-02 07:43:42 +08:00
Chris Tate
3a1ba89194
An unchecked element read of a tuple array (`rows[i].length` with `rows: [number, string][]`) answers the element's optional value, and the computed `.length` path discarded it, so a read past the end printed the tuple's arity. It now holds the receiver and throws Node's TypeError, "Cannot read properties of undefined (reading 'length')", when the element is missing, before answering the arity. The corpus program tuple-length-computed.ts covers a missing element read directly and through a field holding the array.
91 lines
2.5 KiB
TypeScript
91 lines
2.5 KiB
TypeScript
// `.length` of computed tuple expressions: call results, ternaries, `as`
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// assertions, `as const` literals, member reads (fields and accessors) and
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// element reads. The receiver is evaluated once, in order, for its side
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// effects and exceptions, and the length is the tuple's arity.
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const log: string[] = [];
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function pair(tag: string): [number, string] {
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log.push(`pair ${tag}`);
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return [1, tag];
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}
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function triple(): [number, string, boolean] {
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log.push("triple");
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return [1, "x", true];
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}
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function failing(): [number, number] {
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log.push("failing");
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throw new Error("no tuple");
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}
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class Holder {
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plain: [string, string] = ["a", "b"];
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reads = 0;
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get viaAccessor(): [number, number, number] {
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this.reads++;
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log.push("accessor");
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return [this.reads, 2, 3];
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}
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ownLength(): number {
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return this.plain.length + this.viaAccessor.length;
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}
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}
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const nested: [[number, number], [string, string, string]] = [
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[1, 2],
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["a", "b", "c"],
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];
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let flip = 0;
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function pick(): boolean {
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flip++;
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return flip % 2 === 1;
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}
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console.log(pair("call").length);
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console.log((pick() ? triple() : ([0, "", false] as [number, string, boolean])).length);
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console.log((pick() ? triple() : ([0, "", false] as [number, string, boolean])).length);
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console.log(([1, 2, 3] as const).length);
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console.log(([flip, "y"] as [number, string]).length);
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const h = new Holder();
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console.log(h.plain.length, h.viaAccessor.length, h.viaAccessor.length, h.reads);
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console.log(h.ownLength(), h.reads);
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console.log(nested[0].length, nested[1].length, nested.length);
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// Evaluation order inside one expression, and in a loop condition.
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const sum = pair("left").length + triple().length * 10 + pair("right").length * 100;
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console.log(sum);
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let rounds = 0;
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for (let i = 0; i < pair(`loop ${i}`).length; i++) rounds++;
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console.log(rounds);
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console.log(`${pair("template").length}:${typeof triple().length}`);
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// An exception in the receiver propagates; no length is produced.
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try {
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console.log(failing().length);
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} catch (e) {
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console.log("caught", (e as Error).message);
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}
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// An unchecked element read past the end is undefined, so its `length`
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// throws, also through a field holding the array.
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const rows: [number, string][] = [[1, "a"]];
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let missing = 5;
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try {
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console.log(rows[missing].length);
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} catch (e) {
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console.log("missing", String(e));
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}
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console.log("present", rows[0].length);
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const table: { rows: [number, number][] } = { rows: [] };
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try {
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console.log(table.rows[missing - 3].length);
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} catch (e) {
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console.log("missing field", String(e));
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}
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console.log(log.join(" | "));
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