Null pointer in type check

[bwilkerson]

The line numbers have changed, but I believe the code is unchanged.

Count: 1
Session Id: 1474545975743.919

Message: Task failed: StrongModeVerifyUnitTask for source xxx.dart,
StackTrace: Unexpected exception while performing StrongModeVerifyUnitTask for source xxx.dart
#0      AnalysisTask._safelyPerform (package:analyzer/task/model.dart:350)
#1      AnalysisTask.perform (package:analyzer/task/model.dart:238)
#2      AnalysisDriver.performWorkItem (package:analyzer/src/task/driver.dart:284)
#3      AnalysisDriver.performAnalysisTask (package:analyzer/src/task/driver.dart:255)
#4      AnalysisContextImpl.performAnalysisTask.<anonymous closure> (package:analyzer/src/context/context.dart:1231)
#5      _PerformanceTagImpl.makeCurrentWhile (package:analyzer/src/generated/utilities_general.dart:212)
#6      AnalysisContextImpl.performAnalysisTask (package:analyzer/src/context/context.dart:1229)
#7      PerformAnalysisOperation.perform (package:analysis_server/src/operation/operation_analysis.dart:374)
#8      AnalysisServer.performOperation (package:analysis_server/src/analysis_server.dart:889)
#9      Future.Future.<anonymous closure> (dart:async/future.dart:118)
#10     _rootRun (dart:async/zone.dart:1154)
#11     _CustomZone.run (dart:async/zone.dart:1034)
#12     _CustomZone.runGuarded (dart:async/zone.dart:932)
#13     _CustomZone.bindCallback.<anonymous closure> (dart:async/zone.dart:959)
#14     _rootRun (dart:async/zone.dart:1158)
#15     _CustomZone.run (dart:async/zone.dart:1034)
#16     _CustomZone.runGuarded (dart:async/zone.dart:932)
#17     _CustomZone.bindCallback.<anonymous closure> (dart:async/zone.dart:959)
#18     Timer._createTimer.<anonymous closure> (dart:async-patch/timer_patch.dart:16)
#19     _Timer._runTimers (dart:isolate-patch/timer_impl.dart:385)
#20     _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:414)
#21     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:148)

Caused by The null object does not have a getter 'isDynamic'.

NoSuchMethodError: method not found: 'isDynamic'
Receiver: null
Arguments: []
#0      Object._noSuchMethod (dart:core-patch/object_patch.dart:44)
#1      Object.noSuchMethod (dart:core-patch/object_patch.dart:47)
#2      _isTop (package:analyzer/src/generated/type_system.dart:1697)
#3      StrongTypeSystemImpl._isSubtypeOf (package:analyzer/src/generated/type_system.dart:753)
#4      StrongTypeSystemImpl.isSubtypeOf (package:analyzer/src/generated/type_system.dart:431)
#5      CodeChecker.visitFieldFormalParameter (package:analyzer/src/task/strong/checker.dart:384)
#6      FieldFormalParameterImpl.accept (package:analyzer/src/dart/ast/ast.dart:4420)
#7      NodeListImpl.accept (package:analyzer/src/dart/ast/ast.dart:7688)
#8      FormalParameterListImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:4729)
#9      RecursiveAstVisitor.visitFormalParameterList (package:analyzer/dart/ast/visitor.dart:1587)
#10     FormalParameterListImpl.accept (package:analyzer/src/dart/ast/ast.dart:4725)
#11     MethodDeclarationImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:7195)
#12     RecursiveAstVisitor.visitMethodDeclaration (package:analyzer/dart/ast/visitor.dart:1737)
#13     MethodDeclarationImpl.accept (package:analyzer/src/dart/ast/ast.dart:7187)
#14     NodeListImpl.accept (package:analyzer/src/dart/ast/ast.dart:7688)
#15     ClassDeclarationImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:1915)
#16     RecursiveAstVisitor.visitClassDeclaration (package:analyzer/dart/ast/visitor.dart:1425)
#17     CodeChecker.visitClassDeclaration (package:analyzer/src/task/strong/checker.dart:303)
#18     ClassDeclarationImpl.accept (package:analyzer/src/dart/ast/ast.dart:1847)
#19     NodeListImpl.accept (package:analyzer/src/dart/ast/ast.dart:7688)
#20     CompilationUnitImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:2446)
#21     CodeChecker.visitCompilationUnit (package:analyzer/src/task/strong/checker.dart:315)
#22     StrongModeVerifyUnitTask.internalPerform (package:analyzer/src/task/dart.dart:6335)
#23     AnalysisTask._safelyPerform (package:analyzer/task/model.dart:338)
#24     AnalysisTask.perform (package:analyzer/task/model.dart:238)
#25     AnalysisDriver.performWorkItem (package:analyzer/src/task/driver.dart:284)
#26     AnalysisDriver.performAnalysisTask (package:analyzer/src/task/driver.dart:255)
#27     AnalysisContextImpl.performAnalysisTask.<anonymous closure> (package:analyzer/src/context/context.dart:1231)
#28     _PerformanceTagImpl.makeCurrentWhile (package:analyzer/src/generated/utilities_general.dart:212)
#29     AnalysisContextImpl.performAnalysisTask (package:analyzer/src/context/context.dart:1229)
#30     PerformAnalysisOperation.perform (package:analysis_server/src/operation/operation_analysis.dart:374)
#31     AnalysisServer.performOperation (package:analysis_server/src/analysis_server.dart:889)
#32     Future.Future.<anonymous closure> (dart:async/future.dart:118)
#33     _rootRun (dart:async/zone.dart:1154)
#34     _CustomZone.run (dart:async/zone.dart:1034)
#35     _CustomZone.runGuarded (dart:async/zone.dart:932)
#36     _CustomZone.bindCallback.<anonymous closure> (dart:async/zone.dart:959)
#37     _rootRun (dart:async/zone.dart:1158)
#38     _CustomZone.run (dart:async/zone.dart:1034)
#39     _CustomZone.runGuarded (dart:async/zone.dart:932)
#40     _CustomZone.bindCallback.<anonymous closure> (dart:async/zone.dart:959)
#41     Timer._createTimer.<anonymous closure> (dart:async-patch/timer_patch.dart:16)
#42     _Timer._runTimers (dart:isolate-patch/timer_impl.dart:385)
#43     _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:414)
#44     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:148)

[jmesserly]

@bwilkerson -- any idea how we could have ended up with a FieldFormalParameter that has a null type?

it's supposed to be inferred from the field type. Worst case it will be dynamic not null, but the time it reaches CodeChecker (which is fairly late in the task model)

[bwilkerson]

No. It's a little hard to tell which type is null without valid line numbers.

• It's possible that the parameter has a type that is undefined (C(undefinedType this.field)).
• It's possible that the parameter references a field with an unknown type.
• It's possible that the parameter references a name that is not a field.
  In all those cases I would have expected that the type would have been converted into dynamic, but I haven't verified that.

It's also possible that there's another bug somewhere that's causing the information to be erased after it's been computed and then not re-computed.

[jmesserly]

not sure if we'll be able to take action on this now, so much has/is changing in the code base. if it shows up again we can investigate further.