[pigeon] ArgumentError when using a Map with enum keys

[gianlucaparadise]

Steps to Reproduce

1. Define an enum YourEnum
2. Define a class YourObject with a Map<YourEnum?,String?> field
3. Define a pigeon API with a method that takes YourObject as input
4. Create an instance of YourObject, fill the map field and call your method
5. Error: The MessageCodec is not able to encode your argument

You can also check this repository with a sample app:

1. Clone the repo
2. Run the tests under test/pigeon_test.dart

Expected results: I expected to use a Map with enum as key

Actual results: The Map can't be encoded

Code sample

Pigeon API definition:

enum MessageKey {
  title,
  subtitle,
  description,
}

class Message {
  int? id;
  Map<MessageKey?, String?>? additionalProperties;
}

@HostApi()
abstract class HostApiBridge {
  void sendMessage(Message message);
}

API use:

final api = HostApiBridge();

Message message = Message()
  ..id = 1
  ..additionalProperties = {
    MessageKey.title: "title",
    MessageKey.subtitle: "subtitle",
    MessageKey.description: "description",
  };

api.sendMessage(message);

A working sample is available in this repository.

Logs

Invalid argument: Instance of 'MessageKey'

When the exception was thrown, this was the stack:
#0      StandardMessageCodec.writeValue (package:flutter/src/services/message_codecs.dart:426:7)
#1      _HostApiBridgeCodec.writeValue (package:pigeon_issue_example/host_api.dart:45:13)
#2      StandardMessageCodec.writeValue.<anonymous closure> (package:flutter/src/services/message_codecs.dart:422:9)
#3      _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:400:8)
#4      StandardMessageCodec.writeValue (package:flutter/src/services/message_codecs.dart:421:13)
#5      _HostApiBridgeCodec.writeValue (package:pigeon_issue_example/host_api.dart:45:13)
#6      StandardMessageCodec.writeValue.<anonymous closure> (package:flutter/src/services/message_codecs.dart:423:9)
#7      _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:400:8)
#8      StandardMessageCodec.writeValue (package:flutter/src/services/message_codecs.dart:421:13)
#9      _HostApiBridgeCodec.writeValue (package:pigeon_issue_example/host_api.dart:45:13)
#10     _HostApiBridgeCodec.writeValue (package:pigeon_issue_example/host_api.dart:42:7)
#11     StandardMessageCodec.writeValue (package:flutter/src/services/message_codecs.dart:416:9)
#12     _HostApiBridgeCodec.writeValue (package:pigeon_issue_example/host_api.dart:45:13)
#13     StandardMessageCodec.encodeMessage (package:flutter/src/services/message_codecs.dart:314:5)
#14     BasicMessageChannel.send (package:flutter/src/services/platform_channel.dart:56:71)
#15     HostApiBridge.sendMessage (package:pigeon_issue_example/host_api.dart:75:23)
#16     main.<anonymous closure> (file:///Users/your.name/mydev/pigeon_issue_sample/pigeon_issue_example/test/pigeon_test.dart:25:9)
#17     main.<anonymous closure> (file:///Users/your.name/mydev/pigeon_issue_sample/pigeon_issue_example/test/pigeon_test.dart:14:49)
#18     testWidgets.<anonymous closure>.<anonymous closure> (package:flutter_test/src/widget_tester.dart:176:29)
<asynchronous suspension>
<asynchronous suspension>
(elided one frame from package:stack_trace)

Flutter Analyze:

Analyzing pigeon_issue_example...                                       
No issues found! (ran in 3.0s)

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• No issues found!

[danagbemava-nc]

Reproducible using sample provided by OP above.

/cc @gaaclarke

flutter doctor -v

[✓] Flutter (Channel stable, 2.5.3, on macOS 11.6 20G165 darwin-arm, locale en-GB)
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    • Framework revision 18116933e7 (4 weeks ago), 2021-10-15 10:46:35 -0700
    • Engine revision d3ea636dc5
    • Dart version 2.14.4

[✓] Android toolchain - develop for Android devices (Android SDK version 31.0.0)
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    • Platform android-31, build-tools 31.0.0
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[✓] Xcode - develop for iOS and macOS
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[✓] Chrome - develop for the web
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• No issues found!

[✓] Flutter (Channel master, 2.6.0-12.0.pre.688, on macOS 11.6 20G165 darwin-arm, locale en-GB)
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[✓] Android toolchain - develop for Android devices (Android SDK version 31.0.0)
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    • Java binary at: /Applications/Android Studio.app/Contents/jre/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)
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[✓] Connected device (2 available)
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• No issues found!

[gnprice]

Based on flutter/packages#527, it looks like there were two issues here:

• Pigeon doesn't yet support enums as type arguments for collections. That's now tracked as [pigeon] Add support for collections of enums #133728 .
• If you tried to use an enum there, Pigeon wouldn't give a useful up-front error, and instead you'd get an unhelpful exception. That's what [pigeon] Made using enums in type arguments an error, added workaround packages#527 was meant to fix.

So, closing this issue — it's partly been fixed, and what's left is now a duplicate of #133728.

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.