fix(@angular-devkit/architect): complete builders on the next event loop iteration

Waiting to complete the builder until the next tick allows the logging
subscription to flush and provide queued logging entries to the builder
consumer.

(cherry picked from commit ecdbe72)

Author: clydin

packages/angular_devkit/architect/src/create-builder.ts

@@ -8,7 +8,7 @@
 
 import { analytics, experimental, json, logging } from '@angular-devkit/core';
 import { Observable, Subscription, from, isObservable, of, throwError } from 'rxjs';
-import { tap } from 'rxjs/operators';
+import { mergeMap, tap } from 'rxjs/operators';
 import {
   BuilderContext,
   BuilderHandlerFn,
@@ -223,6 +223,12 @@ export function createBuilder<OptT = json.JsonObject, OutT extends BuilderOutput
                 progress({ state: BuilderProgressState.Running, current: total }, context);
                 progress({ state: BuilderProgressState.Stopped }, context);
               }),
+              mergeMap(async (value) => {
+                // Allow the log queue to flush
+                await new Promise<void>(setImmediate);
+
+                return value;
+              }),
             )
             .subscribe(
               (message) => observer.next(message as OutT),

packages/angular_devkit/architect/src/index_spec.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import { json, schema } from '@angular-devkit/core';
+import { json, logging, schema } from '@angular-devkit/core';
 import { timer } from 'rxjs';
 import { map, take, tap, toArray } from 'rxjs/operators';
 import { promisify } from 'util';
@@ -209,6 +209,36 @@ describe('architect', () => {
     expect(all.length).toBe(10);
   });
 
+  it('propagates all logging entries', async () => {
+    const logCount = 100;
+
+    testArchitectHost.addBuilder(
+      'package:test-logging',
+      createBuilder(async (_, context) => {
+        for (let i = 0; i < logCount; ++i) {
+          context.logger.info(i.toString());
+        }
+
+        return { success: true };
+      }),
+    );
+
+    const logger = new logging.Logger('test-logger');
+    const logs: string[] = [];
+    logger.subscribe({
+      next(entry) {
+        logs.push(entry.message);
+      },
+    });
+    const run = await architect.scheduleBuilder('package:test-logging', {}, { logger });
+    expect(await run.result).toEqual(jasmine.objectContaining({ success: true }));
+    await run.stop();
+
+    for (let i = 0; i < logCount; ++i) {
+      expect(logs[i]).toBe(i.toString());
+    }
+  });
+
   it('reports errors in the builder', async () => {
     testArchitectHost.addBuilder(
       'package:error',