[native_assets_builder] Write hook stdout and stderr to disk

pkgs/native_assets_builder/lib/src/build_runner/build_runner.dart

@@ -487,12 +487,13 @@ ${e.message}
       '--config=${inputFile.toFilePath()}',
       if (resources != null) resources.toFilePath(),
     ];
+    final wrappedLogger = await _createFileStreamingLogger(input);
     final result = await runProcess(
       filesystem: _fileSystem,
       workingDirectory: workingDirectory,
       executable: dartExecutable,
       arguments: arguments,
-      logger: logger,
+      logger: wrappedLogger,
       includeParentEnvironment: false,
       environment: environment,
     );
@@ -556,6 +557,32 @@ ${e.message}
     }
   }
 
+  Future<Logger> _createFileStreamingLogger(HookInput input) async {
+    final stdoutFile =
+        _fileSystem.file(input.outputDirectory.resolve('../stdout.txt'));
+    await stdoutFile.writeAsString('');
+    final stderrFile =
+        _fileSystem.file(input.outputDirectory.resolve('../stderr.txt'));
+    await stderrFile.writeAsString('');
+    final wrappedLogger = Logger.detached('')
+      ..level = Level.ALL
+      ..onRecord.listen((record) async {
+        logger.log(record.level, record.message);
+        if (record.level <= Level.INFO) {
+          await stdoutFile.writeAsString(
+            '${record.message}\n',
+            mode: FileMode.append,
+          );
+        } else {
+          await stderrFile.writeAsString(
+            '${record.message}\n',
+            mode: FileMode.append,
+          );
+        }
+      });
+    return wrappedLogger;
+  }
+
   /// Compiles the hook to kernel and caches the kernel.
   ///
   /// If any of the Dart source files, or the package config changed after

pkgs/native_assets_builder/test/build_runner/build_runner_test.dart

@@ -45,6 +45,20 @@ void main() async {
                   '${Platform.pathSeparator}build.dart',
             ]));
         expect(result.encodedAssets.length, 1);
+
+        // Check that invocation logs are written to disk.
+        final packgeBuildDirectory = Directory.fromUri(
+            packageUri.resolve('.dart_tool/native_assets_builder/native_add/'));
+        final buildDirectory =
+            packgeBuildDirectory.listSync().single as Directory;
+        final stdoutFile =
+            File.fromUri(buildDirectory.uri.resolve('stdout.txt'));
+        final stderrFile =
+            File.fromUri(buildDirectory.uri.resolve('stderr.txt'));
+        expect(stdoutFile.existsSync(), true);
+        expect(stdoutFile.readAsStringSync(), contains('Some stdout.'));
+        expect(stderrFile.existsSync(), true);
+        expect(stderrFile.readAsStringSync(), contains('Some stderr.'));
       }
 
       // Trigger a build, should not invoke anything.

pkgs/native_assets_builder/test_data/native_add/hook/build.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:io';
+
 import 'package:logging/logging.dart';
 import 'package:native_assets_cli/native_assets_cli.dart';
 import 'package:native_toolchain_c/native_toolchain_c.dart';
@@ -25,5 +27,7 @@ void main(List<String> arguments) async {
           print('${record.level.name}: ${record.time}: ${record.message}');
         }),
     );
+    stdout.writeln('Some stdout.');
+    stderr.writeln('Some stderr.');
   });
 }