[nodejs/auto] Fix incremental behavior of onStdout (#10678)

* Fix incrementality of onStdout

* Test that onOutput is called more than once

* Add a CHANGELOG entry

CHANGELOG_PENDING.md

@@ -7,3 +7,9 @@
 
 - Fix invalid resource type on `pulumi convert` to Go
   [#10670](https://github.com/pulumi/pulumi/pull/10670)
+
+- [auto/nodejs] `onOutput` is now called incrementally as the
+  underyling Pulumi process produces data, instead of being called
+  once at the end of the process execution. This restores behavior
+  that regressed since 3.39.0.
+  [#10678](https://github.com/pulumi/pulumi/pull/10678)

sdk/nodejs/automation/cmd.ts

@@ -56,14 +56,23 @@ export async function runPulumiCmd(
     const env = { ...process.env, ...additionalEnv };
 
     try {
-        const { stdout, stderr, exitCode } = await execa("pulumi", args, { env, cwd });
+        const proc = execa("pulumi", args, { env, cwd });
+
+        if (onOutput && proc.stdout) {
+            proc.stdout!.on("data", (data: any) => {
+                if (data && data.toString) {
+                    data = data.toString();
+                }
+                onOutput(data);
+            });
+        }
+
+        const { stdout, stderr, exitCode } = await proc;
         const commandResult = new CommandResult(stdout, stderr, exitCode);
         if (exitCode !== 0) {
             throw createCommandError(commandResult);
         }
-        if (onOutput) {
-            onOutput(stdout);
-        }
+
         return commandResult;
     } catch (err) {
         const error = err as Error;

sdk/nodejs/tests/automation/cmd.spec.ts

@@ -1,4 +1,4 @@
-// Copyright 2016-2021, Pulumi Corporation.
+// Copyright 2016-2022, Pulumi Corporation.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -13,17 +13,19 @@
 // limitations under the License.
 
 import * as assert from "assert";
-import * as sinon from "sinon";
 import { runPulumiCmd } from "../../automation";
 import { asyncTest } from "../util";
 
 describe("automation/cmd", () => {
     it("calls onOutput when provided to runPulumiCmd", asyncTest(async () => {
-        const spy = sinon.spy();
-        await runPulumiCmd(["version"], ".", {}, spy);
-
-        assert.ok(spy.calledOnce);
-        assert.strictEqual(spy.firstCall.firstArg, spy.lastCall.lastArg);
+        let output = "";
+        let numCalls = 0;
+        await runPulumiCmd(["--help"], ".", {}, (data: string) => {
+            output += data;
+            numCalls += 1;
+        });
+        assert.ok(numCalls > 1, `expected numCalls > 1, got ${numCalls}`);
+        assert.match(output, new RegExp("Usage[:]"));
+        assert.match(output, new RegExp("[-][-]verbose"));
     }));
 });
-