error: Not a constant expression - only at runtime

[zoechi]

I use a class with a const constructor with new and it complains that it is not a constant expression even though none should be required.

I'm also pretty sure I didn't make changes related to this code since a few months and it worked so far.

DartAnalyzer doesn't show any hints or warnings

here _createSplashScreen() is called

class AppWidgetState extends State<AppWidget> {
  @override
  Widget build(BuildContext context) => new StreamBuilder<AppController>(
      stream: widget.appController.onStateChange,
      builder: (context, _) => widget.appController.isSplashScreenVisible
          ? _createSplashScreen()
          : _createApp(context));

the implementation

  MaterialApp _createSplashScreen() =>
      new MaterialApp(home: new SplashScreen.tenant());

the class with the const constructor

class SplashScreen extends StatelessWidget {
  const SplashScreen.base();

  factory SplashScreen.tenant() {
    switch (Tenant.tenant) {
      case Tenant.origin:
        return const SplashScreenOrigin();
      default:
        return const SplashScreen.base();
    }
  }

class SplashScreenOrigin extends SplashScreen {
  const SplashScreenOrigin() : super.base();

The error message is not very helpful. See also #33438

I/flutter (13702): 8 2018-07-17 14:29:27.436094 SEVERE lookatmybaby_flutter.sentry_error_reporter: Context: building StreamBuilder<AppController<EntityMixin<dynamic>>>(dirty, state: _StreamBuilderBaseState<AppController<EntityMixin<dynamic>>, AsyncSnapshot<AppController<EntityMixin<dynamic>>>>#05069), library: widgets library
I/flutter (13702):     error: 'package:lookatmybaby_flutter/widgets/screens/splash_screen.dart': error: Not a constant expression.
I/flutter (13702): #0      AppWidgetState._createSplashScreen (package:lookatmybaby_flutter/widgets/app_widget.dart:134:33)
I/flutter (13702): #1      AppWidgetState.build.<anonymous closure> (package:lookatmybaby_flutter/widgets/app_widget.dart:47:13)
I/flutter (13702): #2      StreamBuilder.build (package:flutter/src/widgets/async.dart:408:74)
I/flutter (13702): #3      _StreamBuilderBaseState.build (package:flutter/src/widgets/async.dart:124:48)
I/flutter (13702): #4      StatefulElement.build (package:flutter/src/widgets/framework.dart:3743:27)
I/flutter (13702): #5      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3655:15)
I/flutter (13702): #6      Element.rebuild (package:flutter/src/widgets/framework.dart:3508:5)
I/flutter (13702): #7      ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3635:5)
I/flutter (13702): #8      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3782:11)
I/flutter (13702): #9      ComponentElement.mount (package:flutter/src/widgets/framework.dart:3630:5)
I/flutter (13702): #10     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2920:14)

[zoechi]

[✓] Flutter (Channel master, v0.5.8-pre.58, on Mac OS X 10.13.6 17G65, locale en-AT)
• Flutter version 0.5.8-pre.58 at /Users/zoechi/flutter/flutter
• Framework revision 85f09f6 (9 hours ago), 2018-07-16 22:42:06 -0700
• Engine revision c5a63d28bf
• Dart version 2.0.0-dev.67.0.flutter-84ca27a09e

[✓] Android toolchain - develop for Android devices (Android SDK 27.0.3)
• Android SDK at /usr/local/opt/android-sdk
• Android NDK at /usr/local/opt/android-sdk/ndk-bundle
• Platform android-27, build-tools 27.0.3
• ANDROID_HOME = /usr/local/opt/android-sdk
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)
• All Android licenses accepted.

[✓] iOS toolchain - develop for iOS devices (Xcode 9.4.1)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 9.4.1, Build version 9F2000
• ios-deploy 1.9.2
• CocoaPods version 1.5.3

[✓] Android Studio (version 3.1)
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin version 23.1.2
• Dart plugin version 173.4700
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)

[✓] IntelliJ IDEA Ultimate Edition (version 2018.1.5)
• IntelliJ at /Applications/IntelliJ IDEA.app
• Flutter plugin version 26.0.2
• Dart plugin version 181.4892.1

[✓] Connected devices (1 available)
• Android SDK built for x86 • emulator-5554 • android-x86 • Android 8.1.0 (API 27) (emulator)

• No issues found!

[zoechi]

Can't reproduce anymore.

[zoechi]

Still the same. Made a mistake when testing.

[kmillikin]

I can't reproduce this from just the snippets of code above.

Unfortunately, the same error message "Not a constant expression." is used in both the front end compiler and the Dart VM, so I can't even localize the problem from the (bad) stack trace.

Is it possible we could get a standalone reproduction?

[zoechi]

Thanks for having a look.
I'll try to come up with a reproduction, but it might take a while.

[zoechi]

The simplest reproduction I was able to come up with is

import 'package:flutter/widgets.dart';

void main() {
  print(SplashScreen.tenant());
}

abstract class SplashScreen extends StatelessWidget {
  const SplashScreen.base();

  factory SplashScreen.tenant() => const SplashScreenFoo();
}

class SplashScreenFoo extends SplashScreen {
  const SplashScreenFoo() : super.base();

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
  }
}

I wasn't able to reproduce without extending from StatelessWidget, so this code can only run in Flutter.
I tried to replace StatelessWidget with a custom class built after StatelessWidget but I haven't found what part actually caused the issue.

[zoechi]

Currently at

$ flutter doctor -v
[✓] Flutter (Channel master, v0.7.4-pre.21, on Mac OS X 10.13.6 17G65, locale en-AT)
• Flutter version 0.7.4-pre.21 at /Users/zoechi/flutter/flutter
• Framework revision 7cebaac (4 days ago), 2018-08-29 21:53:39 -0700
• Engine revision 252da48082
• Dart version 2.1.0-dev.3.0.flutter-760a9690c2

[✓] Android toolchain - develop for Android devices (Android SDK 28.0.1)
• Android SDK at /usr/local/opt/android-sdk
• Android NDK at /usr/local/opt/android-sdk/ndk-bundle
• Platform android-28, build-tools 28.0.1
• ANDROID_HOME = /usr/local/opt/android-sdk
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)
• All Android licenses accepted.

[✓] iOS toolchain - develop for iOS devices (Xcode 9.4.1)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 9.4.1, Build version 9F2000
• ios-deploy 1.9.2
• CocoaPods version 1.5.3

[✓] Android Studio (version 3.1)
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin version 23.1.2
• Dart plugin version 173.4700
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)

[✓] IntelliJ IDEA Ultimate Edition (version 2018.2)
• IntelliJ at /Applications/IntelliJ IDEA.app
• Flutter plugin version 26.0.3
• Dart plugin version 182.3569.4

[✓] Connected devices (1 available)
• Android SDK built for x86 • emulator-5554 • android-x86 • Android 8.1.0 (API 27) (emulator)

• No issues found!