mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-11-08 08:44:37 +08:00
Malte Ubl
e52688095d
String.fromCharCode, String.fromCodePoint, the global isNaN and isFinite, DataView offsets and values, and typed-array slice/subarray bounds took a `number | undefined` value (an out-of-range read the checker types as number) through a checked narrow, which threw "undefined is not representable" or refused to compile. Node converts undefined with ToNumber: code unit 0, a RangeError for fromCodePoint, isNaN true, offset 0; an undefined slice end is the length. The Math argument conversion becomes a shared helper that also handles field reads and any other value lowered as a number-or-undefined union.
96 lines
3.4 KiB
TypeScript
96 lines
3.4 KiB
TypeScript
// Builtins that convert a number argument with ToNumber see a missing
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// read (an out-of-range typed-array or array read the checker types as
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// `number`) as NaN, ToNumber's answer for undefined: String.fromCharCode
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// yields code unit 0, fromCodePoint throws a RangeError, Math answers NaN,
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// isNaN is true. The missing value reaches them from a module binding, a
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// local, a class field and a record field.
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const base: number = process.argv.length;
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const chars = new Uint16Array(4);
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chars[0] = 108;
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chars[1] = 66;
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const nums: number[] = [7];
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const far = base + 100;
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const missing = chars[far];
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const present = chars[1];
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const missingNum = nums[far];
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function show(label: string, value: unknown): void {
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console.log(label, typeof value === "string" ? JSON.stringify(value) : value);
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}
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function attempt(label: string, run: () => unknown): void {
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try {
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show(label, run());
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} catch (e) {
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console.log(label, "threw", (e as Error).name, (e as Error).message);
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}
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}
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// String.fromCharCode / fromCodePoint.
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show("fcc module", String.fromCharCode(chars[0], missing));
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show("fcc single", String.fromCharCode(missing));
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show("fcc present", String.fromCharCode(chars[0], present));
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show("fcc array", String.fromCharCode(missingNum, 65));
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attempt("fcp module", () => String.fromCodePoint(missing));
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show("fcp present", String.fromCodePoint(present));
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// Math functions.
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show("abs", Math.abs(missing));
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show("floor", Math.floor(missingNum));
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show("max", Math.max(missing, 1));
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show("min3", Math.min(1, 2, missing));
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show("imul", Math.imul(missing, 3));
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show("pow", Math.pow(present, 2));
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show("hypot", Math.hypot(missing, 3));
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// The global number predicates convert; the Number statics do not.
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show("isNaN", isNaN(missing));
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show("isNaN present", isNaN(present));
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show("isFinite", isFinite(missing));
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show("isFinite present", isFinite(present));
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show("Number.isNaN", Number.isNaN(missing));
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show("Number.isFinite", Number.isFinite(missing));
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// DataView offsets (ToIndex) and values (ToNumber).
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const view = new DataView(new ArrayBuffer(4));
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view.setUint8(1, 9);
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show("dv get", view.getUint8(missing));
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view.setUint8(missing, 5);
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show("dv set offset", view.getUint8(0));
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view.setUint8(2, missing);
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show("dv set value", view.getUint8(2));
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// Typed-array ranges: a missing start is 0, a missing end is the length.
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show("slice start", chars.slice(missing).length);
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show("slice end", chars.slice(1, missing).length);
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show("subarray start", chars.subarray(missing).length);
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show("subarray end", chars.subarray(2, missing).length);
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// The same reads held in a local, a class field and a record field.
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function local(i: number, label: string): void {
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let code: number | undefined = 0;
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code = chars[i];
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show(`local fcc ${label}`, String.fromCharCode(97, code));
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show(`local max ${label}`, Math.max(code, 1));
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show(`local isNaN ${label}`, isNaN(code));
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}
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local(far, "missing");
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local(1, "present");
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class Cursor {
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code: number | undefined = 0;
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}
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const cursor = new Cursor();
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cursor.code = chars[far];
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show("field fcc", String.fromCharCode(97, cursor.code));
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show("field abs", Math.abs(cursor.code));
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cursor.code = chars[1];
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show("field fcc present", String.fromCharCode(97, cursor.code));
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const record: { code: number | undefined } = { code: 0 };
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record.code = chars[far];
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show("record fcc", String.fromCharCode(97, record.code));
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show("record max", Math.max(record.code, 1));
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show("record isNaN", isNaN(record.code));
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