Derived class that calls super() then returns a Proxy trips "Must call super constructor" — blocks node-fetch after #10759

[proggeramlug]

With #10759 fixed (PR #10807), node-fetch@3.3.2 gets past the Function.prototype.call was called on a value that is not a function failure and hits the next one:

ReferenceError: Must call super constructor in derived class before accessing 'this'
                or returning from derived constructor

raised inside node-fetch's real Headers.js. Pre-existing and separate from #10759 — reported rather than fixed, per that task's scope.

The shape

node-fetch's Headers is a derived class whose constructor calls super(...) and then returns a Proxy wrapping this:

export default class Headers extends URLSearchParams {
  constructor(init) {
    // ...normalise init into `result`...
    super(result);
    return new Proxy(this, { get(target, p, receiver) { /* ... */ } });
  }
}

That is legal JavaScript and Node executes it without complaint. Perry raises the derived-constructor guard anyway.

Worth noting the guard is doing its job in general — this is not a claim that the check is wrong, but that something in this shape (a super() call followed by a constructor-return override, with a Proxy as the returned value) is not being recognised as having satisfied it.

Why it is worth attention beyond node-fetch

The constructor-return-override is not exotic. Returning a Proxy from a constructor is the standard way to give a class a dynamic property surface, and doing it from a derived class — after super() — is exactly what a subclass of a builtin must do. Anything wrapping a builtin this way is a candidate.

Reproduction

mkdir nf-probe && cd nf-probe
npm install node-fetch@3.3.2
# package.json: { "perry": { "compilePackages": ["node-fetch"] } }
# fixture.ts: import fetch from "node-fetch"; then a GET against a local node:http server
perry compile fixture.ts -o fixture && ./fixture

A package-independent reduction is the obvious first step and was not attempted: a derived class extending a builtin, calling super(), then returning new Proxy(this, {...}). If that reproduces, node-fetch is incidental.

Status

This is the second distinct defect in node-fetch's path, after #10759. Real-source node-fetch remains blocked, and its binding should not be removed until this is resolved. #10759's fix is correct and complete for what it claims — its gap test covers the same derived-class-plus-Proxy shape and passes byte-for-byte against Node — but the package needs both.

[proggeramlug]

Re-tested this against current main (47ade47327) with the real node-fetch@3.3.2 source graph (22 compiled modules: node-fetch, data-uri-to-buffer, fetch-blob, formdata-polyfill, node-domexception, and web-streams-polyfill).

The reported derived-constructor failure is no longer reproducible: Headers gets through super(...) and its Proxy return without the Must call super constructor error. The existing test_gap_10759_urlsearchparams_prototype_method_value.ts reduction also passes.

The full local-HTTP fixture now reaches a later, separate HTTP integration failure:

RESULT: ERROR Error: Invalid response handle
    at new __AnonShape_105fb05143d2f2d2 (<anonymous>)

This result establishes only that the original symptom does not reproduce on current main; the cause of the difference from the earlier run is unknown. The current node-fetch blocker is tracked separately in #10887.

[proggeramlug]

Closing this report because its specific derived-constructor failure no longer reproduces on current main; the reason for the difference from the original run is unknown. The newly observed node-fetch failure is tracked independently in #10887.

[proggeramlug]

Reopening after a fully coherent rebuild of current main (f88acdaa1b) reproduced the original Must call super constructor failure with the clean public-entry node-fetch@3.3.2 fixture. The earlier non-reproduction used a compiler/runtime build containing the pending #10886 changes, so it was not a valid pristine-main result. #10887 remains the next observed blocker on top of that pending fix.

[proggeramlug]

Confirmed reproducing cleanly on current main while re-validating node-fetch after its original blocker (#10759) landed. Full fixture: node-fetch@3.3.2, perry.compilePackages: ["node-fetch"], a self-hosted http.createServer + fetch() round trip (GET /json, POST /echo). Compiles and links (needs the full auto-optimize path — see #10671 for a separate, unrelated link-coherence gap this package also hits under PERRY_NO_AUTO_OPTIMIZE=1), then:

node-fetch version: 3.3.2
ReferenceError: Must call super constructor in derived class before accessing 'this' or returning from derived constructor
    at <anonymous>

Node runs the identical fixture cleanly (GET json: {"hello":"world"}, POST echo: {"a":1}). This is the last blocker standing between node-fetch and a full real-source pass — once this lands, re-validating with the same fixture should confirm the package end-to-end.