Call untyped write completion callbacks with the error argument (#2585)

packages/compiler/src/frontend/lowering/lower-stream.ts

@@ -6966,11 +6966,15 @@ export function lowerStreamMethodCall(
     const lowerWriteCb = (cbArg: ts.Expression): IrExpr => {
       // The stream ignores what the callback returns (`() => count++`, a
       // stored function returning a value): the value is discarded.
+      // An untyped callback (a function a JavaScript module returned) is
+      // called unbound with the error argument, as Node calls it.
       const raw = lowerer.lowerExpr(cbArg);
       const cb =
-        raw.type.kind === "func" && raw.type.ret.kind !== "void" && raw.type.params.length <= 1
-          ? lowerer.coerceToExpected(raw, funcOf(raw.type.params, VOID))
-          : raw;
+        raw.type.kind === "dyn"
+          ? lowerer.coerceToExpected(raw, funcOf([DYN], VOID))
+          : raw.type.kind === "func" && raw.type.ret.kind !== "void" && raw.type.params.length <= 1
+            ? lowerer.coerceToExpected(raw, funcOf(raw.type.params, VOID))
+            : raw;
       if (cb.type.kind !== "func" || cb.type.ret.kind !== "void" || cb.type.params.length > 1) {
         lowerer.noLowering(
           "write completion callbacks of this shape",

packages/compiler/test/ts7/baselines/order-parity/tests/corpus/stream-dynamic-write-callback/main.ts.json

@@ -0,0 +1,7 @@
+{
+ "order": [
+  "<repo>/tests/corpus/stream-dynamic-write-callback/report.js",
+  "<repo>/tests/corpus/stream-dynamic-write-callback/main.ts"
+ ],
+ "diags": []
+}

tests/corpus/stream-dynamic-write-callback/main.ts

@@ -0,0 +1,28 @@
+// Write completion callbacks from a JavaScript module run unbound with
+// Node's arguments: null after a successful write, the _write error after a
+// failed one, and the write-after-end error. Their return value is ignored.
+import { Writable } from "node:stream";
+import { makeReporter } from "./report.js";
+
+const lines: string[] = [];
+const sink = new Writable({
+  write(chunk: Buffer, _encoding: string, callback: (error?: Error | null) => void): void {
+    callback(chunk.toString() === "bad" ? new Error("rejected") : null);
+  },
+});
+sink.on("error", (error) => lines.push(`error event ${error.message}`));
+sink.write("good", makeReporter(lines, "good"));
+sink.write("bad", "utf8", makeReporter(lines, "bad"));
+
+const ended = new Writable({
+  write(_chunk: Buffer, _encoding: string, callback: (error?: Error | null) => void): void {
+    callback();
+  },
+});
+ended.on("error", () => lines.push("ended error event"));
+ended.end();
+ended.write("late", makeReporter(lines, "late"));
+
+setTimeout(() => {
+  for (const line of lines) console.log(line);
+}, 5);

tests/corpus/stream-dynamic-write-callback/report.js

@@ -0,0 +1,11 @@
+// A write completion callback built in JavaScript: it records how it was
+// called. Module code is strict, so an unbound call sees `this` undefined.
+export function makeReporter(lines, label) {
+  return function (...args) {
+    const error = args[0];
+    lines.push(
+      `${label} args=${args.length} error=${error === null ? "null" : error === undefined ? "undefined" : error.message} this=${typeof this}`,
+    );
+    return "ignored";
+  };
+}

tests/harness/corpus-costs/stream-dynamic-write-callback/main.ts.json

@@ -0,0 +1 @@
+{ "plain": 1833, "san": 2753 }