NPE during inference

[bwilkerson]

Dart analysis server, SDK version 1.15.0-dev.0.0, server version 1.14.0, error: Task failed: PartiallyResolveUnitReferencesTask for source ...
Unexpected exception while performing PartiallyResolveUnitReferencesTask for source ...
#0      AnalysisTask._safelyPerform (package:analyzer/task/model.dart:328)
#1      AnalysisTask.perform (package:analyzer/task/model.dart:218)
#2      AnalysisDriver.performWorkItem (package:analyzer/src/task/driver.dart:274)
#3      AnalysisDriver.performAnalysisTask (package:analyzer/src/task/driver.dart:249)
#4      AnalysisContextImpl.performAnalysisTask.<anonymous closure> (package:analyzer/src/context/context.dart:1122)
#5      _PerformanceTagImpl.makeCurrentWhile (package:analyzer/src/generated/utilities_general.dart:194)
#6      AnalysisContextImpl.performAnalysisTask (package:analyzer/src/context/context.dart:1120)
#7      PerformAnalysisOperation.perform (package:analysis_server/src/operation/operation_analysis.dart:371)
#8      AnalysisServer.performOperation (package:analysis_server/src/analysis_server.dart:807)
#9      Future.Future.<anonymous closure> (dart:async/future.dart:118)
#10     _rootRun (dart:async/zone.dart:891)
#11     _CustomZone.run (dart:async/zone.dart:790)
#12     _CustomZone.runGuarded (dart:async/zone.dart:696)
#13     _CustomZone.bindCallback.<anonymous closure> (dart:async/zone.dart:721)
#14     _rootRun (dart:async/zone.dart:895)
#15     _CustomZone.run (dart:async/zone.dart:790)
#16     _CustomZone.runGuarded (dart:async/zone.dart:696)
#17     _CustomZone.bindCallback.<anonymous closure> (dart:async/zone.dart:721)
#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 'element'.

NoSuchMethodError: method not found: 'element'
Receiver: null
Arguments: []
#0      Object._noSuchMethod (dart:core-patch/object_patch.dart:42)
#1      Object.noSuchMethod (dart:core-patch/object_patch.dart:45)
#2      InferenceContext._matchTypes.match (package:analyzer/src/generated/resolver.dart:5587)
#3      InferenceContext._matchTypes.match (package:analyzer/src/generated/resolver.dart:5603)
#4      InferenceContext._matchTypes (package:analyzer/src/generated/resolver.dart:5629)
#5      InferenceContext.matchTypes (package:analyzer/src/generated/resolver.dart:5505)
#6      ResolverVisitor.visitInstanceCreationExpression (package:analyzer/src/generated/resolver.dart:9081)
#7      InstanceCreationExpressionImpl.accept (package:analyzer/src/dart/ast/ast.dart:5948)
#8      AstNodeImpl._safelyVisitChild (package:analyzer/src/dart/ast/ast.dart:935)
#9      VariableDeclarationImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:10449)
#10     ResolverVisitor.visitNode (package:analyzer/src/generated/resolver.dart:9212)
#11     PartialResolverVisitor.visitNode (package:analyzer/src/generated/resolver.dart:7665)
#12     UnifyingAstVisitor.visitVariableDeclaration (package:analyzer/dart/ast/visitor.dart:1844)
#13     ScopedVisitor.visitVariableDeclaration (package:analyzer/src/generated/resolver.dart:10757)
#14     ResolverVisitor.visitVariableDeclaration (package:analyzer/src/generated/resolver.dart:9328)
#15     VariableDeclarationImpl.accept (package:analyzer/src/dart/ast/ast.dart:10443)
#16     NodeListImpl.accept (package:analyzer/src/dart/ast/ast.dart:7410)
#17     VariableDeclarationListImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:10544)
#18     ResolverVisitor.visitNode (package:analyzer/src/generated/resolver.dart:9212)
#19     PartialResolverVisitor.visitNode (package:analyzer/src/generated/resolver.dart:7665)
#20     UnifyingAstVisitor.visitVariableDeclarationList (package:analyzer/dart/ast/visitor.dart:1848)
#21     ResolverVisitor.visitVariableDeclarationList (package:analyzer/src/generated/resolver.dart:9354)
#22     VariableDeclarationListImpl.accept (package:analyzer/src/dart/ast/ast.dart:10538)
#23     AstNodeImpl._safelyVisitChild (package:analyzer/src/dart/ast/ast.dart:935)
#24     TopLevelVariableDeclarationImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:9762)
#25     ResolverVisitor.visitNode (package:analyzer/src/generated/resolver.dart:9212)
#26     PartialResolverVisitor.visitNode (package:analyzer/src/generated/resolver.dart:7665)
#27     UnifyingAstVisitor.visitTopLevelVariableDeclaration (package:analyzer/dart/ast/visitor.dart:1826)
#28     ResolverVisitor.visitTopLevelVariableDeclaration (package:analyzer/src/generated/resolver.dart:9312)
#29     PartialResolverVisitor.visitTopLevelVariableDeclaration (package:analyzer/src/generated/resolver.dart:7672)
#30     TopLevelVariableDeclarationImpl.accept (package:analyzer/src/dart/ast/ast.dart:9757)
#31     ResolverVisitor.visitCompilationUnit (package:analyzer/src/generated/resolver.dart:8610)
#32     CompilationUnitImpl.accept (package:analyzer/src/dart/ast/ast.dart:2360)
#33     PartiallyResolveUnitReferencesTask.internalPerform (package:analyzer/src/task/dart.dart:3718)
#34     AnalysisTask._safelyPerform (package:analyzer/task/model.dart:318)
#35     AnalysisTask.perform (package:analyzer/task/model.dart:218)
#36     AnalysisDriver.performWorkItem (package:analyzer/src/task/driver.dart:274)
#37     AnalysisDriver.performAnalysisTask (package:analyzer/src/task/driver.dart:249)
#38     AnalysisContextImpl.performAnalysisTask.<anonymous closure> (package:analyzer/src/context/context.dart:1122)
#39     _PerformanceTagImpl.makeCurrentWhile (package:analyzer/src/generated/utilities_general.dart:194)
#40     AnalysisContextImpl.performAnalysisTask (package:analyzer/src/context/context.dart:1120)
#41     PerformAnalysisOperation.perform (package:analysis_server/src/operation/operation_analysis.dart:371)
#42     AnalysisServer.performOperation (package:analysis_server/src/analysis_server.dart:807)
#43     Future.Future.<anonymous closure> (dart:async/future.dart:118)
#44     _rootRun (dart:async/zone.dart:891)
#45     _CustomZone.run (dart:async/zone.dart:790)
#46     _CustomZone.runGuarded (dart:async/zone.dart:696)
#47     _CustomZone.bindCallback.<anonymous closure> (dart:async/zone.dart:721)
#48     _rootRun (dart:async/zone.dart:895)
#49     _CustomZone.run (dart:async/zone.dart:790)
#50     _CustomZone.runGuarded (dart:async/zone.dart:696)
#51     _CustomZone.bindCallback.<anonymous closure> (dart:async/zone.dart:721)
#52     Timer._createTimer.<anonymous closure> (dart:async-patch/timer_patch.dart:16)
#53     _Timer._runTimers (dart:isolate-patch/timer_impl.dart:385)
#54     _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:414)
#55     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:148)

[jmesserly]

I'm guessing classTypeName.type is null, probably because the class name wasn't defined: List<int> x = new SomeUnknownName() ... I'll see if I can make a repro

[jmesserly]

Huh, I tried things like this:

class C<T> implements SomeUnknownName<T> {}
main() {
  C<int> x = new C();
}

Unfortunately it doesn't reproduce the problem (I may be on an older build). Here's a question -- how is it possible to get a null in the superclass/supermixin/superinterface chain? That seems like what's happening. Haven't gotten to dig in further.

[bwilkerson]

That's probably the bug, but the most likely cause is invalid code, such as

class C<T> implements DoesNotExist {}

or even

class C<T> implements {}

[bwilkerson]

I still don't know how to reproduce this, but it looks like we're getting to a point where t1 has a null superclass but isn't equal to the type for Object. I can't think of a way to get into that state, though.

[jmesserly]

I'm guessing this is stale? if not we can reopen