WeakValueMap: replacing an entry doesn't unregister the old value, causing erroneous deletion

[mvduin]

When replacing an existing entry of a WeakValueMap, the old value is not unregistered from the FinalizationRegistry so when it later get garbage-collected the corresponding entry gets erroneously deleted from the map.

Test case using node --expose-gc:

import { WeakValueMap } from 'weakref';
import assert from 'node:assert';

function next_job() {
    return new Promise( resolve => setImmediate( resolve ) );
}

let map = new WeakValueMap;

map.set( 42, {} );  // create entry pointing to fresh garbage

let x = {};

map.set( 42, x );  // overwrite entry with a strongly retained value

await next_job();  // release strong ref on new/dereferenced weakrefs
gc();  // garbage-collect the now-unreferenced old value
await next_job();  // fire finalization callback

assert.strictEqual( map.get( 42 ), x );  // FAILS
assert.strictEqual( map.size, 1 );  // FAILS