From a848a7b349338d91ec3000ccebd3d5bd5d1242b0 Mon Sep 17 00:00:00 2001
From: Chris Tate <chris@ctate.dev>
Date: Sun, 25 Oct 2026 18:44:18 -0500
Subject: [PATCH] Resolve the pipeline promise to undefined for an untyped
 iterable destination

When an untyped destination function returned an async iterable, the
promise form settled its result without a payload, and code that read the
awaited value as an untyped value dereferenced NULL. The promise form for
an untyped destination now resolves to undefined when the destination
returned no promise, or its promise carries no value, as Node does.
---
 packages/runtime/src/scr_stream.c             | 24 +++++++++++++++++--
 .../7509-pipeline-untyped-function-stages.mjs |  5 ++++
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/packages/runtime/src/scr_stream.c b/packages/runtime/src/scr_stream.c
index a7593b551..fb416e5c3 100644
--- a/packages/runtime/src/scr_stream.c
+++ b/packages/runtime/src/scr_stream.c
@@ -5312,13 +5312,31 @@ static void scr_sp_value_inv(ScrClosure *cb, ScrError *err, ScrDyn *value, ScrPr
   scr_promise_release(p);
 }
 
+/* scr_sp_value_inv for an untyped destination (SCR_PIPE_DEST_DYN), whose
+ * result promise carries a dyn value: when the destination returned an
+ * async iterable (no promise), or its promise carries no payload, the
+ * result is undefined, as in Node. */
+static void scr_sp_dyn_value_inv(ScrClosure *cb, ScrError *err, ScrDyn *value,
+                                 ScrPromise *value_p) {
+  if (err != NULL || (value_p != NULL && scr_promise_payload_kind(value_p) != SCR_EXC_NONE)) {
+    scr_sp_value_inv(cb, err, value, value_p);
+    return;
+  }
+  ScrPromise *p = scr_box_get_ref(cb->caps[0]); /* +1 */
+  scr_promise_fulfill_ref(p, scr_dyn_retain(scr_dyn_undefined()), scr_dyn_retain_v,
+                          scr_dyn_release_v, NULL);
+  scr_promise_release(p);
+}
+
 ScrPromise *scr_sp_pipeline_stages(double n, ScrStream **streams, double count,
                                    ScrClosure **stages, double positions, double flags,
                                    double mask, ScrClosure **helpers, ScrClosure *box,
                                    ScrDyn *signal, ScrClosure *abort) {
   ScrPromise *p = scr_promise_new();
   ScrPipeStages fs = scr_pipe_stages_of(count, stages, positions, flags, mask, helpers, box, signal);
-  ScrPipeValInv vi = fs.dest != SCR_PIPE_DEST_STREAM ? &scr_sp_value_inv : NULL;
+  ScrPipeValInv vi = fs.dest == SCR_PIPE_DEST_STREAM ? NULL
+                     : fs.dest == SCR_PIPE_DEST_DYN  ? &scr_sp_dyn_value_inv
+                                                     : &scr_sp_value_inv;
   ScrStream *dst = scr_stream_pipeline_ex((size_t)n, streams, scr_sp_watcher(p), &scr_sp_settle_inv,
                                           true, NULL, NULL, &fs, abort, vi);
   if (dst) scr_stream_release(dst);
@@ -5370,7 +5388,9 @@ ScrPromise *scr_sp_pipeline_stages_opts(double n, ScrStream **streams, double co
   ScrPromise *p = scr_promise_new();
   if (!scr_sp_opts_signal(p, &outer)) return p;
   ScrPipeStages fs = scr_pipe_stages_of(count, stages, positions, flags, mask, helpers, box, signal);
-  ScrPipeValInv vi = fs.dest != SCR_PIPE_DEST_STREAM ? &scr_sp_value_inv : NULL;
+  ScrPipeValInv vi = fs.dest == SCR_PIPE_DEST_STREAM ? NULL
+                     : fs.dest == SCR_PIPE_DEST_DYN  ? &scr_sp_dyn_value_inv
+                                                     : &scr_sp_value_inv;
   ScrStream *dst = scr_stream_pipeline_ex((size_t)n, streams, scr_sp_watcher(p), &scr_sp_settle_inv,
                                           end, outer, add, &fs, abort, vi);
   if (dst) scr_stream_release(dst);
diff --git a/tests/corpus/7509-pipeline-untyped-function-stages.mjs b/tests/corpus/7509-pipeline-untyped-function-stages.mjs
index 18749e55a..590334f90 100644
--- a/tests/corpus/7509-pipeline-untyped-function-stages.mjs
+++ b/tests/corpus/7509-pipeline-untyped-function-stages.mjs
@@ -53,6 +53,11 @@ const out = pipeline(Readable.from(["p1", "p2"]), wrap, (err, value) => {
 console.log("returns a PassThrough", out instanceof PassThrough);
 for await (const chunk of out) console.log("passthrough", chunk);
 
+// an async generator destination in the promise form: the PassThrough
+// takes its values and the promise resolves to undefined
+const promised = await pipelineP(Readable.from(["q1", "q2"]), wrap);
+console.log("generator destination promise", promised, typeof promised);
+
 // a destination whose promise rejects
 try {
   await pipelineP(