Closure-captured numeric params read as 0 inside object-literal `: Date` method (@perryts/mysql MyDateTime.toDate shape)

[proggeramlug]

Repro (MySQL-free, no Fastify, 12 lines)

Drop into /tmp/repro.ts, perry compile repro.ts -o repro && ./repro:

function show(label: string, d: Date) {
  console.log(label, "getTime=", d.getTime(), " iso=", d.toISOString());
}
function makeDT(y: number) {
  return { toDate(): Date {
    return new Date(Date.UTC(y, 4, 15, 17, 29, 35, 402));   // captured `y` reads as 0 inside this method
  } };
}
const d = makeDT(2026).toDate();
console.log("INLINE:", d.getTime());
show("HELPER:", d);

Observed (perry 0.5.914)

INLINE: -62155492224598
HELPER: getTime= -62155492224598  iso= 0000-05-15T17:29:36.598Z

Expected (tsx / node — same source)

INLINE: 1778866175402
HELPER: getTime= 1778866175402  iso= 2026-05-15T17:29:35.402Z

The reconstructed milliseconds -62155492224598 is exactly Date.UTC(0, 4, 15, 17, 29, 35, 402) — i.e. the captured y is read as 0 inside toDate() regardless of the value passed to makeDT(...). All other Date.UTC args are literals and arrive intact; only the closure-captured numeric y is corrupt.

Adding a NaN-guard branch (if (y===0) return new Date(NaN);) confirms it from the other side — makeDT(2026).toDate() returns Invalid Date because the guard sees y === 0.

Where this surfaces in real code

node_modules/@perryts/mysql/src/types/datetime.ts::makeMyDateTime is structurally identical:

function makeMyDateTime(y, mo, d, h, mi, sec, micros, raw) {
  return { year:y, ..., toDate(): Date {
    if (y===0 && mo===0 && d===0) return new Date(NaN);
    return new Date(Date.UTC(y, mo-1, d, h, mi, sec, Math.round(micros/1000)));
  }};
}

So every DATETIME column decoded by @perryts/mysql produces a MyDateTime whose .toDate() returns either Invalid Date (the all-zero guard wins because every captured field reads as 0) or a year-0 garbage Date. Consumers like skelpo-shop-admin's toUser(row) then either crash in downstream formatters or silently store wrong timestamps. This is the proximate cause of the new SIGBUS in the shop-admin signup path at v0.5.914 (filed separately).

Notes from bisecting

• The bug only fires in certain file contexts — a tighter single-function file (function makeDT(...); console.log(makeDT(2026).toDate().getTime()) with no other declarations) compiles correctly. Adding a second function that declares a : Date parameter type, or a few other shapes, makes it manifest reliably. So it's a type-analysis interaction across the module, not a property of the makeDT definition alone.
• Object-literal method with : Date return annotation + closure capture of a numeric outer param is the consistent shape.
• The captured non-numeric references (raw: string in the real makeMyDateTime) appear unaffected — only numeric captures zero out.
• Counterpart shapes that DO work: toDate: (): Date => new Date(Date.UTC(y, ...)) (arrow-property), toDate: function(): Date { ... } (fn-prop), bare function f(y): Date { ... } (standalone fn). The bug is specific to the shorthand-method-in-object-literal-with-: Date-return-and-closure-captured-numeric-params combination.

Context

Surfaced while verifying the v0.5.912 / v0.5.914 #748 fixes against the shop-admin native server. The wait_for_promise condvar fix and the Invalid-Date sentinel both landed correctly — confirmed via the previous minimal repros. This is a separate downstream bug in the same : Date / closure-capture region that's exposed once the Invalid-Date path is correct.

Reproduces deterministically at perry 0.5.914 (HEAD e18cdb07). Happy to add PERRY_DEBUG_* traces if useful — the dynamic-dispatch path for Date.UTC(...) inside the method's body is where I'd start looking (whether captured-arg slots get the f64 they should at the call site).