stream: add comments to pipeline implementation

Fixes: #32039 PR-URL: #32042 Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Matteo Collina <[email protected]> Reviewed-By: James M Snell <[email protected]>

Author: ronag

lib/internal/streams/pipeline.js

@@ -219,6 +219,11 @@ function pipeline(...streams){
 PassThrough=require('_stream_passthrough');
 }
 
+// If the last argument to pipeline is not a stream
+// we must create a proxy stream so that pipeline(...)
+// always returns a stream which can be further
+// composed through `.pipe(stream)`.
+
 constpt=newPassThrough();
 if(isPromise(ret)){
 ret
@@ -253,6 +258,9 @@ function pipeline(...streams){
 }
 }
 
+// TODO(ronag): Consider returning a Duplex proxy if the first argument
+// is a writable. Would improve composability.
+// See, https://github.com/nodejs/node/issues/32020
 returnret;
 }