stream: reject closed only after sink abort settles

lib/internal/webstreams/writablestream.js

@@ -928,6 +928,13 @@ function writableStreamFinishErroring(stream) {
     writableStreamRejectCloseAndClosedPromiseIfNeeded(stream);
     return;
   }
+  // The closed promises are only rejected once the sink's abort algorithm
+  // settles, so materialize them here: deriving them from the 'errored'
+  // state within that window would hand out an already rejected promise.
+  stream[kState].closedPromise ??= PromiseWithResolvers();
+  const writer = stream[kState].writer;
+  if (writer !== undefined)
+    writer[kState].close ??= PromiseWithResolvers();
   PromisePrototypeThen(
     stream[kState].controller[kAbort](abortRequest.reason),
     () => {

test/parallel/test-webstreams-writer-closed-abort-pending.js

@@ -0,0 +1,42 @@
+'use strict';
+
+// The writer's closed promise stays pending until the sink's abort()
+// algorithm settles, even when it is first observed after the stream has
+// already reached the 'errored' state.
+
+const common = require('../common');
+const assert = require('assert');
+const { setImmediate: immediate } = require('timers/promises');
+const { WritableStream } = require('stream/web');
+
+async function main() {
+  const error = new Error('boom');
+  const { promise: abortComplete, resolve: finishAbort } = Promise.withResolvers();
+  const ws = new WritableStream({
+    abort: common.mustCall((reason) => {
+      assert.strictEqual(reason, error);
+      return abortComplete;
+    }),
+  });
+  const writer = ws.getWriter();
+  const aborted = writer.abort(error);
+
+  // Lets the stream finish erroring and call the sink's abort().
+  await immediate();
+
+  let closedSettled = false;
+  const closed = writer.closed.catch(common.mustCall((reason) => {
+    closedSettled = true;
+    assert.strictEqual(reason, error);
+  }));
+
+  await immediate();
+  assert.strictEqual(closedSettled, false);
+
+  finishAbort();
+  await aborted;
+  await closed;
+  assert.strictEqual(closedSettled, true);
+}
+
+main().then(common.mustCall());