refactor(@angular/build): collect and log build errors in library builder

packages/angular/build/src/builders/library/builder.ts

@@ -24,6 +24,7 @@ import { getSupportedBrowsers } from '../../utils/supported-browsers';
 import { assertCompatibleAngularVersion } from '../../utils/version';
 import type { BuildWatcher } from '../../utils/watcher';
 import { normalizeLibraryOptions } from './options';
+import type { BuildActionResult } from './pipeline/build-action';
 import { updateWatchedEntryPoints } from './pipeline/entry-points';
 import type { createComponentStylesheetBundlerForLibrary } from './pipeline/stylesheet-bundler';
 import { loadPackageJson } from './pipeline/utils';
@@ -185,6 +186,17 @@ export async function* executeLibraryBuilder(
   }
 }
 
+/**
+ * Executes a single build iteration with progress reporting, logs any resulting
+ * messages, and registers newly discovered files with the watcher.
+ *
+ * @param message Progress spinner message to display while building.
+ * @param actionContext The build action context and state.
+ * @param withProgress Progress wrapper function (`withSpinner` or `withNoProgress`).
+ * @param watcher Optional file watcher for watch mode.
+ * @param buildAction The library build action function to execute.
+ * @returns A promise resolving to the Architect `BuilderOutput`.
+ */
 async function executeBuild(
   message: string,
   actionContext: import('./pipeline/build-action').BuildActionContext,
@@ -196,13 +208,16 @@ async function executeBuild(
   const { context, watchedCompilationFiles, isWatchMode, options } = actionContext;
 
   try {
-    await withProgress(message, () => buildAction(actionContext));
-    logBuildResult(context.logger, startTime, true, options.outputPath);
-    if (isWatchMode) {
+    const result = await withProgress(message, () => buildAction(actionContext));
+    logMessages(context.logger, result);
+
+    const success = result.errors.length === 0;
+    logBuildResult(context.logger, startTime, success, options.outputPath);
+    if (success && isWatchMode) {
       logCumulativeDurations();
     }
 
-    return { success: true };
+    return { success };
   } catch (error) {
     assertIsError(error);
     logBuildResult(context.logger, startTime, false);
@@ -300,6 +315,7 @@ async function* runWatchLoop(
         assertIsError(error);
         await buildState.singleProgramCache?.compilationInstance.update?.(changedFiles);
         buildState.hasEmittedManifests = false;
+
         yield {
           success: false,
           error: `Failed to reload 'package.json': ${error.message}`,
@@ -343,8 +359,36 @@ async function* runWatchLoop(
   }
 }
 
+/**
+ * Logs informational, warning, and error messages produced during a build iteration.
+ *
+ * @param logger The Architect logger API.
+ * @param result The build action result containing logs, warnings, and errors.
+ */
+function logMessages(
+  logger: logging.LoggerApi,
+  { logs, warnings, errors }: BuildActionResult,
+): void {
+  if (logs.length) {
+    logger.info(logs.join('\n'));
+  }
+
+  if (warnings.length) {
+    logger.warn(warnings.join('\n'));
+  }
+
+  if (errors.length) {
+    logger.error(errors.join('\n'));
+  }
+}
+
 /**
  * Logs the build completion time and status.
+ *
+ * @param logger The Architect logger API.
+ * @param startTime High-resolution timestamp recorded when the build iteration started.
+ * @param success Whether the build iteration succeeded without errors.
+ * @param outputPath Optional output directory path to log on successful builds.
  */
 function logBuildResult(
   logger: logging.LoggerApi,