return Scaffold(appBar: AppBar());

return Scaffold(
  appBar: AppBar(),
);

$ flutter doctor -v
[✓] Connected device (3 available)
    • sdk gphone64 arm64 (mobile) • emulator-5554                        • android-arm64  • Android 12 (API 31)
      (emulator)
    • iPhone 13 (mobile)          • ECD4C6D8-7BD4-4FC8-BA1F-78A769C823AD • ios            •
      com.apple.CoreSimulator.SimRuntime.iOS-15-0 (simulator)
    • Chrome (web)                • chrome                               • web-javascript • Google Chrome 95.0.4638.69

import 'package:flutter/foundation.dart';

if (kDebugMode) {
  print('debug code');
}

onTap: () {
  print('押されたよ');
},

onTap: () {
  Navigator.push(
    context,
    MaterialPageRoute(
      builder: (context) => const OtherPage(),
    ),
  );
},

onTap: () {
  Navigator.push(
    context,
    MaterialPageRoute(
      builder: (context) => const OtherPage('Foo'),
    ),
  );
},

class TalkRoom extends StatefulWidget {
+  final String name;
-  const TalkRoom({Key? key}) : super(key: key);
+ const TalkRoom({Key? key, required this.name}) : super(key: key);

  @override
  _TalkRoomState createState() => _TalkRoomState();
}

Container(
  constraints: BoxConstraints(
      maxWidth: MediaQuery.of(context).size.width * 0.6),
  ),
  //
)

ListView.builder(
  reverse: true,
  //
)

ListView.builder(
+ shrinkWrap: true,
  reverse: true,
  //
)

ListView.builder(
+ physics: const RangeMaintainingScrollPhysics(),
  shrinkWrap: true,
  reverse: true,
  //
)

import 'package:firebase_core/firebase_core.dart';
import 'firebase_options.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp(
    options: DefaultFirebaseOptions.currentPlatform,
  );
  runApp(const MyApp());
}

$ firebase projects:list
✖ Preparing the list of your Firebase projects

Error: Failed to list Firebase projects. See firebase-debug.log for more info.

$ firebase login --reauth

$ firebase logout
$ firebase login

[!] CocoaPods could not find compatible versions for pod "cloud_firestore":

[!] Automatically assigning platform `iOS` with version `9.0` on target `Runner` because no platform was specified. Please specify a platform for this target in your Podfile. See `https://guides.cocoapods.org/syntax/podfile.html#platform`.

# Uncomment this line to define a globalf platform for your project
-  // platform :ios, '9.0'
+  platform :ios, '14.0'

Launching lib/main.dart on sdk gphone arm64 in debug mode...
Running Gradle task 'assembleDebug'...
Warning: Mapping new ns http://schemas.android.com/repository/android/common/02 to old ns http://schemas.android.com/repository/android/common/01
Warning: Mapping new ns http://schemas.android.com/repository/android/generic/02 to old ns http://schemas.android.com/repository/android/generic/01
Warning: Mapping new ns http://schemas.android.com/sdk/android/repo/addon2/02 to old ns http://schemas.android.com/sdk/android/repo/addon2/01
Warning: Mapping new ns http://schemas.android.com/sdk/android/repo/repository2/02 to old ns http://schemas.android.com/sdk/android/repo/repository2/01
Warning: Mapping new ns http://schemas.android.com/sdk/android/repo/sys-img2/02 to old ns http://schemas.android.com/sdk/android/repo/sys-img2/01
/Users/harapeko/hobby/flutter_udemy_chat/android/app/src/debug/AndroidManifest.xml Error:
	uses-sdk:minSdkVersion 16 cannot be smaller than version 19 declared in library [:cloud_firestore] /Users/harapeko/hobby/flutter_udemy_chat/build/cloud_firestore/intermediates/library_manifest/debug/AndroidManifest.xml as the library might be using APIs not available in 16
	Suggestion: use a compatible library with a minSdk of at most 16,
		or increase this project's minSdk version to at least 19,
		or use tools:overrideLibrary="io.flutter.plugins.firebase.firestore" to force usage (may lead to runtime failures)

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:processDebugMainManifest'.
> Manifest merger failed : uses-sdk:minSdkVersion 16 cannot be smaller than version 19 declared in library [:cloud_firestore] /Users/harapeko/hobby/flutter_udemy_chat/build/cloud_firestore/intermediates/library_manifest/debug/AndroidManifest.xml as the library might be using APIs not available in 16
  	Suggestion: use a compatible library with a minSdk of at most 16,
  		or increase this project's minSdk version to at least 19,
  		or use tools:overrideLibrary="io.flutter.plugins.firebase.firestore" to force usage (may lead to runtime failures)

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 12s

The plugin cloud_firestore requires a higher Android SDK version.
Fix this issue by adding the following to the file /Users/harapeko/hobby/flutter_udemy_chat/android/app/build.gradle:
android {
  defaultConfig {
    minSdkVersion 19
  }
}

Note that your app won't be available to users running Android SDKs below 19.
Alternatively, try to find a version of this plugin that supports these lower versions of the Android SDK.
Exception: Gradle task assembleDebug failed with exit code 1

defaultConfig {
    // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
    applicationId "dev.harapeko.flutter_udemy_chat"
-   minSdkVersion flutter.minSdkVersion
+   minSdkVersion math.Max(flutter.minSdkVersion, 30)
    targetSdkVersion flutter.targetSdkVersion
    versionCode flutterVersionCode.toInteger()
    versionName flutterVersionName
}

BUILD FAILED in 24s
[!] Your project requires a newer version of the Kotlin Gradle plugin.
    Find the latest version on https://kotlinlang.org/docs/gradle.html#plugin-and-versions, then update /Users/harapeko/hobby/flutter_udemy_chat/android/build.gradle:
    ext.kotlin_version = '<latest-version>'
Exception: Gradle task assembleDebug failed with exit code 1

buildscript {
- ext.kotlin_version = '1.3.50'
+ ext.kotlin_version = '1.6.10'
    repositories {
        google()
        mavenCentral()
    }

Error: ADB exited with exit code 1
Performing Streamed Install

adb: failed to install /Users/harapeko/hobby/flutter_udemy_chat/build/app/outputs/flutter-apk/app.apk: Failure [INSTALL_FAILED_OLDER_SDK: Failed parse during installPackageLI: /data/app/vmdl141932564.tmp/base.apk (at Binary XML file line #7): Requires newer sdk version #31 (current version is #30)]
Error launching application on sdk gphone arm64.