runtime: `class M extends Map {}` / `extends Set` — instance has no methods at all (`m.set(...)` throws TypeError)

[proggeramlug]

Summary

class M extends Map {} produces an instance with no Map methods at all. Calling any of them throws. Same for Set. This is not an override-ordering problem — subclassing these builtins is simply broken, with no override involved.

Confirmed on clean origin/main.

Repro

class M extends Map {}
const m = new M();
m.set("a", 1);
console.log("map subclass get:", m.get("a"), "size:", m.size);

	output
node 26	map subclass get: 1 size: 1
perry main	TypeError: set is not a function

Set behaves the same way.

Context

Surfaced while fixing #6316 (subclass method overriding a native base method was silently bypassed). During that work an affected-base matrix was measured:

base	override runs?	super.<m>() reaches base?
EventEmitter	fixed in #6322	fixed in #6322
node:stream (Readable/Writable/…)	fixed in #6322	fixed in #6322
EventTarget	fixed in #6301 / #6311	—
Array	yes	no — super.push() no-ops
Error	yes	no — super.toString() → undefined
Promise	yes	no — super.then not a function
Map / Set	n/a — subclassing itself is broken	no

So Map/Set are the worst case in that table: the earlier-reported super failure for them is a symptom of the instance having no methods at all, not of dispatch ordering.

Related: #6316 (override bypass, fixed in #6322), #6301 (extends EventTarget, fixed in #6311). Note #6232/#6260 added class X extends Array support — Map/Set appear to have never gotten the equivalent.