CFE crash in wild

[ThinkDigitalSoftware]

Don't know how to reproduce.

Unhandled exception:
NoSuchMethodError: The getter 'length' was called on null.
Receiver: null
Tried calling: length
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)
#1 setParents (package:kernel/ast.dart:9651:29)
#2 new ForElement (package:front_end/src/fasta/kernel/collections.dart:201:5)
#3 Forest.createForElement (package:front_end/src/fasta/kernel/forest.dart:241:16)
#4 BodyBuilder.endForControlFlow (package:front_end/src/fasta/kernel/body_builder.dart:2796:34)
#5 ForComplete.parse (package:_fe_analyzer_shared/src/parser/literal_entry_info_impl.dart:123:21)
#6 Parser.parseLiteralSetOrMapSuffix (package:_fe_analyzer_shared/src/parser/parser_impl.dart:5246:26)
#7 Parser.parsePrimary (package:_fe_analyzer_shared/src/parser/parser_impl.dart:5011:14)
#8 Parser.parseUnaryExpression (package:_fe_analyzer_shared/src/parser/parser_impl.dart:4870:12)
#9 Parser.parsePrecedenceExpression (package:_fe_analyzer_shared/src/parser/parser_impl.dart:4604:13)
#10 Parser.parseExpression (package:_fe_analyzer_shared/src/parser/parser_impl.dart:4545:13)
#11 BodyBuilder.parseSingleExpression (package:front_end/src/fasta/kernel/body_builder.dart:1376:20)
#12 SourceLoader.buildExpression (package:front_end/src/fasta/source/source_loader.dart:485:21)

#13 IncrementalCompiler.compileExpression. (package:front_end/src/fasta/incremental_compiler.dart:1645:61)
#14 CompilerContext.runInContext.. (package:front_end/src/fasta/compiler_context.dart:123:46)
#15 new Future.sync (dart:async/future.dart:223:31)
#16 CompilerContext.runInContext. (package:front_end/src/fasta/compiler_context.dart:123:19)
#17 _rootRun (dart:async/zone.dart:1190:13)
#18 _CustomZone.run (dart:async/zone.dart:1093:19)
#19 _runZoned (dart:async/zone.dart:1630:10)
#20 runZoned (dart:async/zone.dart:1550:10)
#21 CompilerContext.runInContext (package:front_end/src/fasta/compiler_context.dart:122:12)
#22 IncrementalCompiler.compileExpression (package:front_end/src/fasta/incremental_compiler.dart:1570:26)
#23 IncrementalCompiler.compileExpression (package:vm/incremental_compiler.dart:205:23)
#24 FrontendCompiler.compileExpression (package:frontend_server/frontend_server.dart:925:44)
#25 _FlutterFrontendCompiler.compileExpression (package:flutter_frontend_server/server.dart:74:22)
#26 listenAndCompile. (package:frontend_server/frontend_server.dart:1296:20)
#27 _RootZone.runUnaryGuarded (dart:async/zone.dart:1384:10)
#28 _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:357:11)
#29 _BufferingStreamSubscription._add (dart:async/stream_impl.dart:285:7)
#30 _SinkTransformerStreamSubscription._add (dart:async/stream_transformers.dart:69:11)
#31 _EventSinkWrapper.add (dart:async/stream_transformers.dart:15:11)
#32 _StringAdapterSink.add (dart:convert/string_conversion.dart:238:11)
#33 _LineSplitterSink._addLines (dart:convert/line_splitter.dart:155:13)
#34 _LineSplitterSink.addSlice (dart:convert/line_splitter.dart:130:5)
#35 StringConversionSinkMixin.add (dart:convert/string_conversion.dart:163:5)
#36 _SinkTransformerStreamSubscription._handleData (dart:async/stream_transformers.dart:121:24)
#37 _RootZone.runUnaryGuarded (dart:async/zone.dart:1384:10)
#38 _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:357:11)
#39 _BufferingStreamSubscription._add (dart:async/stream_impl.dart:285:7)
#40 _SinkTransformerStreamSubscription._add (dart:async/stream_transformers.dart:69:11)
#41 _EventSinkWrapper.add (dart:async/stream_transformers.dart:15:11)
#42 _StringAdapterSink.add (dart:convert/string_conversion.dart:238:11)
#43 _StringAdapterSink.addSlice (dart:convert/string_conversion.dart:243:7)
#44 _Utf8ConversionSink.addSlice (dart:convert/string_conversion.dart:317:20)
#45 _Utf8ConversionSink.add (dart:convert/string_conversion.dart:310:5)
#46 _ConverterStreamEventSink.add (dart:convert/chunked_conversion.dart:72:18)
#47 _SinkTransformerStreamSubscription._handleData (dart:async/stream_transformers.dart:121:24)
#48 _RootZone.runUnaryGuarded (dart:async/zone.dart:1384:10)
#49 _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:357:11)
#50 _BufferingStreamSubscription._add (dart:async/stream_impl.dart:285:7)
#51 _SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:808:19)
#52 _StreamController._add (dart:async/stream_controller.dart:682:7)
#53 _StreamController.add (dart:async/stream_controller.dart:624:5)
#54 _Socket._onData (dart:io-patch/socket_patch.dart:2044:41)
#55 _RootZone.runUnaryGuarded (dart:async/zone.dart:1384:10)
#56 _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:357:11)
#57 _BufferingStreamSubscription._add (dart:async/stream_impl.dart:285:7)
#58 _SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:808:19)
#59 _StreamController._add (dart:async/stream_controller.dart:682:7)
#60 _StreamController.add (dart:async/stream_controller.dart:624:5)
#61 new _RawSocket. (dart:io-patch/socket_patch.dart:1580:33)
#62 _NativeSocket.issueReadEvent.issue (dart:io-patch/socket_patch.dart:1076:14)
#63 _microtaskLoop (dart:async/schedule_microtask.dart:41:21)
#64 _startMicrotaskLoop (dart:async/schedule_microtask.dart:50:5)
#65 _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:118:13)
#66 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:169:5)
the Dart compiler exited unexpectedly.
the Dart compiler exited unexpectedly.

Flutter 1.22.5 • channel stable • https://github.com/flutter/flutter.git
Framework • revision 7891006299 (4 weeks ago) • 2020-12-10 11:54:40 -0800
Engine • revision ae90085a84
Tools • Dart 2.10.4

[vsmenon]

@ThinkDigitalSoftware - can you give some context of what you were doing when you saw this error? Building a debug version of the app? Release version? Debugging an app - e.g., typing an expression in the REPL?

What version of Dart and/or Flutter? Android/ios/web?

[ThinkDigitalSoftware]

Hi, I was paused on a breakpoint In debug mode running on an android device. Let me get the version.

[ThinkDigitalSoftware]

What version of Dart and/or Flutter? Android/ios/web?

Added the Flutter and Dart version to the description now.

[johnniwinther]

The situation is triggered by code like {for (;;) e;}; (a UI collection for-loop) but I haven't been able to find exactly what to put in the for-loop to trigger the crash.

[ThinkDigitalSoftware]

And it's an enormous project and I wasn't even working on the UI section of the code... Wish I could help

[johnniwinther]

From the stack trace the crash happened when evaluating an expression during debugging so the source code isn't even in your project code. The most likely cause is some expression with syntax error being compiled and the crash comes from the recovery we try to make. For instance if you write for (;, we would try to complete it to for (;;); in order to parse it, and this recovery crashes the compiler later in its pipeline.