Dynamic failures in analysis server during `dart fix`

[eernstg]

I hope this is useful, even though I haven't made any attempts to create a minimal scenario. I've experienced a number of dynamic errors raised in the analysis server (2.19.0-421.0.dev) as follows. Run this command:

> cd $SDK/tests/language
> dart fix --dry-run .

The current commit of the SDK repo was e7985b28e9007bc4bfc9f1e5084c1b5376617fe8 .

One example run provided this output:

Computing fixes in language (dry run)...
Error from the analysis server: Exception while getting bulk fixes: type 'BooleanLiteralImpl' is not a subtype of type '_ParenthesizedCondition' in type cast
#0      AstBuilder.endSwitchStatement (package:analyzer/src/fasta/ast_builder.dart:3051:27)
#1      Parser.parseSwitchStatement (package:_fe_analyzer_shared/src/parser/parser_impl.dart:8278:14)
#2      Parser.parseStatementX (package:_fe_analyzer_shared/src/parser/parser_impl.dart:5250:14)
#3      Parser.parseStatement (package:_fe_analyzer_shared/src/parser/parser_impl.dart:5198:20)
#4      Parser.parseFunctionBody (package:_fe_analyzer_shared/src/parser/parser_impl.dart:5103:15)
#5      Parser.parseTopLevelMethod (package:_fe_analyzer_shared/src/parser/parser_impl.dart:3573:13)
#6      Parser.parseTopLevelMemberImpl (package:_fe_analyzer_shared/src/parser/parser_impl.dart:3318:14)
#7      Parser.parseTopLevelDeclarationImpl (package:_fe_analyzer_shared/src/parser/parser_impl.dart:574:14)
#8      Parser.parseUnit (package:_fe_analyzer_shared/src/parser/parser_impl.dart:392:15)
#9      Parser.parseCompilationUnit2 (package:analyzer/src/generated/parser.dart:107:32)
#10     Parser.parseCompilationUnit (package:analyzer/src/generated/parser.dart:103:12)
#11     FileState._parse (package:analyzer/src/dart/analysis/file_state.dart:709:23)
#12     FileState.parse (package:analyzer/src/dart/analysis/file_state.dart:489:14)
#13     FileState._getUnlinkedUnit (package:analyzer/src/dart/analysis/file_state.dart:655:16)
#14     FileState.refresh (package:analyzer/src/dart/analysis/file_state.dart:526:27)
#15     FileSystemState._newFile (package:analyzer/src/dart/analysis/file_state.dart:1435:10)
#16     FileSystemState.getFileForPath2 (package:analyzer/src/dart/analysis/file_state.dart:1267:14)
#17     FileSystemState.getFileForPath (package:analyzer/src/dart/analysis/file_state.dart:1251:12)
#18     AnalysisDriver.getResolvedLibrary (package:analyzer/src/dart/analysis/driver.dart:873:27)
#19     AnalysisSessionImpl.getResolvedLibrary (package:analyzer/src/dart/analysis/session.dart:103:26)
#20     BulkFixProcessor.fixErrors (package:analysis_server/src/services/correction/bulk_fix_processor.dart:244:52)
<asynchronous suspension>
#21     EditBulkFixes.handle (package:analysis_server/src/handler/legacy/edit_bulk_fixes.dart:43:20)
<asynchronous suspension>


#0      FileState.parse (package:analyzer/src/dart/analysis/file_state.dart:491:7)
#1      FileState._getUnlinkedUnit (package:analyzer/src/dart/analysis/file_state.dart:655:16)
#2      FileState.refresh (package:analyzer/src/dart/analysis/file_state.dart:526:27)
#3      FileSystemState._newFile (package:analyzer/src/dart/analysis/file_state.dart:1435:10)
#4      FileSystemState.getFileForPath2 (package:analyzer/src/dart/analysis/file_state.dart:1267:14)
#5      FileSystemState.getFileForPath (package:analyzer/src/dart/analysis/file_state.dart:1251:12)
#6      AnalysisDriver.getResolvedLibrary (package:analyzer/src/dart/analysis/driver.dart:873:27)
#7      AnalysisSessionImpl.getResolvedLibrary (package:analyzer/src/dart/analysis/session.dart:103:26)
#8      BulkFixProcessor.fixErrors (package:analysis_server/src/services/correction/bulk_fix_processor.dart:244:52)
<asynchronous suspension>
#9      EditBulkFixes.handle (package:analysis_server/src/handler/legacy/edit_bulk_fixes.dart:43:20)
<asynchronous suspension>


#0      FileState.parse (package:analyzer/src/dart/analysis/file_state.dart:491:7)
#1      FileState._getUnlinkedUnit (package:analyzer/src/dart/analysis/file_state.dart:655:16)
#2      FileState.refresh (package:analyzer/src/dart/analysis/file_state.dart:526:27)
#3      FileSystemState._newFile (package:analyzer/src/dart/analysis/file_state.dart:1435:10)
#4      FileSystemState.getFileForPath2 (package:analyzer/src/dart/analysis/file_state.dart:1267:14)
#5      FileSystemState.getFileForPath (package:analyzer/src/dart/analysis/file_state.dart:1251:12)
#6      AnalysisDriver.getResolvedLibrary (package:analyzer/src/dart/analysis/driver.dart:873:27)
#7      AnalysisSessionImpl.getResolvedLibrary (package:analyzer/src/dart/analysis/session.dart:103:26)
#8      BulkFixProcessor.fixErrors (package:analysis_server/src/services/correction/bulk_fix_processor.dart:244:52)
<asynchronous suspension>
#9      EditBulkFixes.handle (package:analysis_server/src/handler/legacy/edit_bulk_fixes.dart:43:20)
<asynchronous suspension>

The process was stuck at this point (no changes for about half an hour):

> sudo strace -p 160073
strace: Process 160073 attached
futex(0x7fff97b3b4f0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, FUTEX_BITSET_MATCH_ANY) = ? ERESTARTSYS (To be restarted if SA_RESTART is set)

It seems like this procedure will yield many different crashes, perhaps because it will process the input libraries in a different order from time to time. Here is another one:

Computing fixes in language (dry run)...
Error from the analysis server: Exception while getting bulk fixes: Stack Overflow
#0      SubtypeHelper.isSubtypeOf (package:analyzer/src/dart/element/subtype.dart:36:3)
#1      SubtypeHelper.isSubtypeOf (package:analyzer/src/dart/element/subtype.dart:165:11)
#2      SubtypeHelper.isSubtypeOf (package:analyzer/src/dart/element/subtype.dart:285:25)
#3      SubtypeHelper.isSubtypeOf (package:analyzer/src/dart/element/subtype.dart:165:11)
#4      SubtypeHelper.isSubtypeOf (package:analyzer/src/dart/element/subtype.dart:285:25)
#5      SubtypeHelper.isSubtypeOf (package:analyzer/src/dart/element/subtype.dart:165:11)
#6      SubtypeHelper.isSubtypeOf (package:analyzer/src/dart/element/subtype.dart:285:25)
#7      SubtypeHelper.isSubtypeOf (package:analyzer/src/dart/element/subtype.dart:165:11)
...

[srawlins]

CC @scheglov recent changes in switches?

[bwilkerson]

Sounds like there are at least three bugs here:

• the unguarded cast in AstBuilder
• the infinite loop in SubtypeHelper
• the hang in dart fix when the server fails to send a response to the request

[scheglov]

1. The infinite loop in SubtypeHelper has always been there, last time when I looked, I decided that it works as specified, i.e. there is a loop in the spec.

2. I can reproduce the crash with this code:

// @dart = 2.18
void f(Object value) {
  switch (value) {
    case (int a,) when a == 0:
  }
}

It happens because in endCaseExpression we pop components of SwitchPatternCaseImpl only when _featureSet.isEnabled(Feature.patterns), but the parser always pushes "something" for the pattern and when clauses. So, we actually pop the guard expression, and leave the "pattern" (not really, actually ParenthesizedExpression because the parser does not create patterns when not enabled, but still creates something) in the stack.

[bwilkerson]

... I decided that it works as specified, i.e. there is a loop in the spec.

I don't think it's reasonable to say that an infinite loop in the spec means that it's ok for server to crash with a stack overflow. Can we please get that fixed?

@eernstg for the bug in the spec.

[scheglov]

See #46524 which I opened a while ago for tracking.
I updated it with a simple reproduction code.

[scheglov]

https://dart-review.googlesource.com/c/sdk/+/272387 should fix the crash for switch.

[srawlins]

I think this is still P1 because an infinite loop can still occur just by running the simple dart fix command @eernstg provided, in the tests/language directory. But if that's... weird or no one does it or no user has ever reported it, or it's acceptable for a few weeks until we get a change to the language spec, maybe it can be downgraded?

[srawlins]

I'm changing my mind on this one. The infinite loop has been around for ages, and we've only had one user report (internally, also from the language tests directory). I think this is just P2.