Require pipeTo() to properly use the destination queue

index.bs

@@ -643,9 +643,11 @@ ReadableStream(<var>underlyingSource</var> = {}, { <var>size</var>, <var>highWat
          from _reader_.
        * If _reader_ is a <a>BYOB reader</a>, WritableStreamDefaultWriterGetDesiredSize(_writer_) should be used to
          determine the size of the chunks read from _reader_.
-       * Otherwise, WritableStreamDefaultWriterGetDesiredSize(_writer_) may be used to determine the flow rate
-         heuristically, e.g. by delaying reads while it is judged to be "low" compared to the size of chunks that have
-         been typically read.
+       * Reads or writes should not be delayed for reasons other than these backpressure signals.
+         <p class="example" id="example-bad-backpressure">An implementation that waits for each write to successfully
+         complete before proceeding to the next read/write operation violates this recommendation. In doing so, such an
+         implementation makes the <a>internal queue</a> of _dest_ useless, as it ensures _dest_ always contains at most
+         one queued <a>chunk</a>.</p>
      * <strong>Shutdown must stop all activity:</strong> if _shuttingDown_ becomes *true*, the user agent must not
        initiate further reads from _reader_ or writes to _writer_. (Ongoing reads and writes may finish.) In particular,
        the user agent must check the below conditions on *this*.[[state]] and _dest_.[[state]] before performing any

reference-implementation/lib/readable-stream.js

@@ -133,11 +133,10 @@ class ReadableStream {
         return writer._readyPromise.then(() => {
           return ReadableStreamDefaultReaderRead(reader).then(({ value, done }) => {
             if (done === true) {
-              return undefined;
+              return;
             }
 
-            currentWrite = WritableStreamDefaultWriterWrite(writer, value);
-            return currentWrite;
+            currentWrite = WritableStreamDefaultWriterWrite(writer, value).catch(() => {});
           });
         })
         .then(pipeLoop);
@@ -202,17 +201,13 @@ class ReadableStream {
         }
       }
 
-      function waitForCurrentWrite() {
-        return currentWrite.catch(() => {});
-      }
-
       function shutdownWithAction(action, originalIsError, originalError) {
         if (shuttingDown === true) {
           return;
         }
         shuttingDown = true;
 
-        waitForCurrentWrite().then(() => {
+        currentWrite.then(() => {
           return action().then(
             () => finalize(originalIsError, originalError),
             newError => finalize(true, newError)
@@ -227,7 +222,7 @@ class ReadableStream {
         }
         shuttingDown = true;
 
-        waitForCurrentWrite().then(() => {
+        currentWrite.then(() => {
           finalize(isError, error);
         })
         .catch(rethrowAssertionErrorRejection);