stream: return readable stream on promisified pipeline

lib/stream/promises.js

@@ -23,11 +23,15 @@ function pipeline(...streams) {
       signal = options.signal;
     }
 
-    pl(streams, (err, value) => {
+    const stream = pl(streams, (err, value) => {
       if (err) {
         reject(err);
-      } else {
+      } else if (value !== undefined) {
         resolve(value);
+      } else if (stream.readable) {
+        resolve(stream);
+      } else {
+        resolve();
       }
     }, { signal });
   });

test/parallel/test-stream-pipeline.js

@@ -1447,3 +1447,29 @@ const tsp = require('timers/promises');
     assert.strictEqual(text, 'Hello World!');
   }));
 }
+
+{
+  const pipelinePromise = promisify(pipeline);
+
+  async function run() {
+    const read = new Readable({
+      read() {}
+    });
+
+    const duplex = new PassThrough();
+
+    read.push('data');
+    read.push(null);
+
+    const stream = await pipelinePromise(read, duplex);
+
+    let ret = ''
+    for await (const x of stream) {
+      ret += x;
+    }
+
+    assert.strictEqual(ret, 'data');
+  }
+
+  run();
+}