[ffigen] make logger optional

pkgs/ffigen/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 20.0.0-dev.1
+
+- Make the `Logger` argument of `FfiGenerator.generate` optional. It defaults to
+  a logger printing to stdout and stderr.
+
 ## 20.0.0-dev.0
 
 - __Breaking change__: Completely rewrite the public Dart API for FFIgen.

pkgs/ffigen/lib/src/config_provider/config.dart

@@ -118,7 +118,10 @@ final class FfiGenerator {
   });
 
   /// Run this generator.
-  void generate({required Logger? logger, Uri? libclangDylib}) {
+  ///
+  /// If provided, uses [logger] to output logs. Otherwise, uses a default
+  /// logger that streams [Level.WARNING] to stdout and higher levels to stderr.
+  void generate({Logger? logger, Uri? libclangDylib}) {
     return FfiGenGenerator(
       this,
     ).generate(logger: logger, libclangDylib: libclangDylib);

pkgs/ffigen/lib/src/ffigen.dart

@@ -10,13 +10,17 @@ import 'package:logging/logging.dart';
 import 'config_provider.dart' show Config, FfiGenerator;
 import 'context.dart';
 import 'header_parser.dart' show parse;
+import 'logger.dart';
 
 final _ansi = Ansi(Ansi.terminalSupportsAnsi);
 
 extension FfiGenGenerator on FfiGenerator {
   /// Runs the entire generation pipeline for the given config.
-  void generate({required Logger? logger, Uri? libclangDylib}) {
-    logger ??= Logger.detached('dev/null')..level = Level.OFF;
+  ///
+  /// If provided, uses [logger] to output logs. Otherwise, uses a default
+  /// logger that streams [Level.WARNING] to stdout and higher levels to stderr.
+  void generate({Logger? logger, Uri? libclangDylib}) {
+    logger ??= createDefaultLogger();
     final config = Config(this);
     final context = Context(logger, config, libclangDylib: libclangDylib);
 

pkgs/ffigen/lib/src/logger.dart

@@ -0,0 +1,27 @@
+// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
+// 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';
+
+/// Creates a default logger that logs to stdout and stderr.
+Logger createDefaultLogger() {
+  final logger = Logger.detached('FFIgen');
+  logger.level = Level.INFO;
+  logger.onRecord.listen((record) {
+    if (record.level >= Level.WARNING) {
+      stderr.writeln(record.message);
+    } else {
+      stdout.writeln(record.message);
+    }
+    if (record.error != null) {
+      stderr.writeln(record.error);
+    }
+    if (record.stackTrace != null) {
+      stderr.writeln(record.stackTrace);
+    }
+  });
+  return logger;
+}

pkgs/ffigen/pubspec.yaml

@@ -3,7 +3,7 @@
 # BSD-style license that can be found in the LICENSE file.
 
 name: ffigen
-version: 20.0.0-dev.0
+version: 20.0.0-dev.1
 description: >
   Generator for FFI bindings, using LibClang to parse C, Objective-C, and Swift
   files.