Mobx.dart: Code generator fails on type-inferred @observable fields

[Vardiak]

Hello, I'm currently facing a strange issue when trying to upgrade to Flutter 1.11 (channel beta)

➜ flutter packages pub run build_runner build -v
[INFO] Generating build script...
[INFO] Generating build script completed, took 375ms

[INFO] BuildDefinition:Initializing inputs
[INFO] BuildDefinition:Reading cached asset graph...
[INFO] BuildDefinition:Reading cached asset graph completed, took 104ms

[INFO] BuildDefinition:Checking for updates since last build...
[INFO] BuildDefinition:Checking for updates since last build completed, took 822ms

[INFO] Build:Running build...
[INFO] Build:Running build completed, took 46ms

[INFO] Build:Caching finalized dependency graph...
[INFO] Build:Caching finalized dependency graph completed, took 77ms

[SEVERE] mobx_codegen:mobx_generator on [censored] (cached):
Error running StoreGenerator
NoSuchMethodError: The method 'toSource' was called on null.
Receiver: null
Tried calling: toSource()
dart:core                                                               Object.noSuchMethod
package:mobx_codegen/src/type_names.dart 6:62                           findVariableTypeName
package:mobx_codegen/src/store_class_visitor.dart 108:16                StoreClassVisitor.visitFieldElement
package:analyzer/src/dart/element/element.dart 5655:53                  FieldElementImpl.accept
package:analyzer/src/dart/element/element.dart 3877:15                  ElementImpl.safelyVisitChildren
package:analyzer/src/dart/element/element.dart 311:5                    AbstractClassElementImpl.visitChildren
package:analyzer/src/dart/element/element.dart 1264:11                  ClassElementImpl.visitChildren
package:mobx_codegen/src/mobx_codegen_base.dart 80:9                    StoreGenerator._generateCodeFromTemplate
package:mobx_codegen/src/mobx_codegen_base.dart 57:13                   StoreGenerator._generateCodeForMixinStore
dart:core                                                               Iterable.toSet
package:mobx_codegen/src/mobx_codegen_base.dart 20:69                   StoreGenerator.generate
package:source_gen/src/builder.dart 280:35                              _generate
package:source_gen/src/builder.dart 73:15                               _Builder._generateForLibrary
package:source_gen/src/builder.dart 67:11                               _Builder.build
package:build                                                           runBuilder
package:build_runner_core/src/generate/build_impl.dart 491:19           _SingleBuild._runForInput.<fn>.<fn>.<fn>
package:build_runner_core/src/generate/performance_tracker.dart 300:15  _NoOpBuilderActionTracker.trackStage
package:build_runner_core/src/generate/build_impl.dart 489:23           _SingleBuild._runForInput.<fn>.<fn>
package:timing/src/timing.dart 222:44                                   NoOpTimeTracker.track
package:build_runner_core/src/generate/build_impl.dart 446:22           _SingleBuild._runForInput.<fn>
package:pool/pool.dart 127:28                                           Pool.withResource
package:build_runner_core/src/generate/build_impl.dart 442:17           _SingleBuild._runForInput
package:build_runner_core/src/generate/build_impl.dart 380:38           _SingleBuild._runBuilder.<fn>
dart:async                                                              Future.wait
package:build_runner_core/src/generate/build_impl.dart 379:36           _SingleBuild._runBuilder
dart:async                                                              _AsyncAwaitCompleter.start
package:build_runner_core/src/generate/build_impl.dart 377:40           _SingleBuild._runBuilder
package:build_runner_core/src/generate/build_impl.dart 325:20           _SingleBuild._runPhases.<fn>.<fn>
dart:async                                                              _completeOnAsyncReturn
package:build_runner_core/src/generate/build_impl.dart                  _SingleBuild._matchingPrimaryInputs

[SEVERE] Build:
Failed after 224ms
pub finished with exit code 1

#0      throwToolExit (package:flutter_tools/src/base/common.dart:28:3)
#1      _DefaultPub.interactively (package:flutter_tools/src/dart/pub.dart:323:7)
<asynchronous suspension>
#2      PackagesPassthroughCommand.runCommand (package:flutter_tools/src/commands/packages.dart:269:15)
<asynchronous suspension>
#3      FlutterCommand.verifyThenRunCommand (package:flutter_tools/src/runner/flutter_command.dart:556:18)
<asynchronous suspension>
#4      FlutterCommand.run.<anonymous closure> (package:flutter_tools/src/runner/flutter_command.dart:456:33)
<asynchronous suspension>
#5      AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:146:29)
<asynchronous suspension>
#6      _rootRun (dart:async/zone.dart:1124:13)
#7      _CustomZone.run (dart:async/zone.dart:1021:19)
#8      _runZoned (dart:async/zone.dart:1516:10)
#9      runZoned (dart:async/zone.dart:1463:12)
#10     AppContext.run (package:flutter_tools/src/base/context.dart:145:18)
<asynchronous suspension>
#11     FlutterCommand.run (package:flutter_tools/src/runner/flutter_command.dart:446:20)
#12     CommandRunner.runCommand (package:args/command_runner.dart:197:27)
<asynchronous suspension>
#13     FlutterCommandRunner.runCommand.<anonymous closure> (package:flutter_tools/src/runner/flutter_command_runner.dart:416:21)
<asynchronous suspension>
#14     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:146:29)
<asynchronous suspension>
#15     _rootRun (dart:async/zone.dart:1124:13)
#16     _CustomZone.run (dart:async/zone.dart:1021:19)
#17     _runZoned (dart:async/zone.dart:1516:10)
#18     runZoned (dart:async/zone.dart:1463:12)
#19     AppContext.run (package:flutter_tools/src/base/context.dart:145:18)
<asynchronous suspension>
#20     FlutterCommandRunner.runCommand (package:flutter_tools/src/runner/flutter_command_runner.dart:367:19)
<asynchronous suspension>
#21     CommandRunner.run.<anonymous closure> (package:args/command_runner.dart:112:25)
#22     new Future.sync (dart:async/future.dart:222:31)
#23     CommandRunner.run (package:args/command_runner.dart:112:14)
#24     FlutterCommandRunner.run (package:flutter_tools/src/runner/flutter_command_runner.dart:251:18)
#25     run.<anonymous closure>.<anonymous closure> (package:flutter_tools/runner.dart:63:22)
<asynchronous suspension>
#26     _rootRun (dart:async/zone.dart:1124:13)
#27     _CustomZone.run (dart:async/zone.dart:1021:19)
#28     _runZoned (dart:async/zone.dart:1516:10)
#29     runZoned (dart:async/zone.dart:1500:12)
#30     run.<anonymous closure> (package:flutter_tools/runner.dart:61:18)
<asynchronous suspension>
#31     AppContext.run.<anonymous closure> (package:flutter_tools/src/base/context.dart:146:29)
<asynchronous suspension>
#32     _rootRun (dart:async/zone.dart:1124:13)
#33     _CustomZone.run (dart:async/zone.dart:1021:19)
#34     _runZoned (dart:async/zone.dart:1516:10)
#35     runZoned (dart:async/zone.dart:1463:12)
#36     AppContext.run (package:flutter_tools/src/base/context.dart:145:18)
<asynchronous suspension>
#37     runInContext (package:flutter_tools/src/context_runner.dart:65:24)
<asynchronous suspension>
#38     run (package:flutter_tools/runner.dart:50:10)
#39     main (package:flutter_tools/executable.dart:65:9)
<asynchronous suspension>
#40     main (file:///Users/ncabasso/Documents/flutter/packages/flutter_tools/bin/flutter_tools.dart:8:3)
#41     _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:303:32)
#42     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:172:12)

Versions :

mobx: ^0.3.9+3
flutter_mobx: ^0.3.3+3
build_runner: ^1.7.1
mobx_codegen: ^0.3.10+1

[Vardiak]

The issue seems to go away when I remove the @observable decorators on data structures (Set, ObservableList etc.).

[Vardiak]

After further investigation, this seems to be related with the use of the var keyword instead of the actual type.

[shyndman]

Can you post a snippet? I'll get it fixed up.

[shyndman]

@observable
var foo = ObservableSet()

Something like that?

[Vardiak]

@observable
var foo = ObservableSet()

Something like that?

Yes !

[shyndman]

Cool. I'll get that fixed up. I'll post back here when the PR/release goes up.

[shyndman]

I'm going to take a stab at fixing this quick and dirty now, but I also posted on the analyzer's tracker to see if there's a more elegant approach.
https://github.com/dart-lang/sdk/issues/39927

[shyndman]

This fix is in PR. Should be merged in the next couple of days.

[shyndman]

Thanks for your patience on this. mobx_codegen 0.3.12 is being published as we speak, which resolves this issue.