[internal error] Parser exception: Collection was modified; enumeration operation may not execute

[keyboardDrummer]

https://github.com/dafny-lang/dafny/actions/runs/8520037939/job/23335354897?pr=5284

There was a concurrent collection modification exception, but sadly only part of the exception is shown in the log:

[xUnit.net 00:03:27.83]         --- End of stack trace from previous location ---
  Failed Microsoft.Dafny.LanguageServer.IntegrationTest.Various.ConcurrentInteractionsTest.VerificationErrorDetectedAfterCanceledSave [188 ms]
  Error Message:
   Assert.Equal() Failure
          ↓ (pos 0)
Expected: assertion might not hold
Actual:   [internal error] Parser exception: Collec···
          ↑ (pos 0)
  Stack Trace:

[keyboardDrummer]

More logging PR, to show the entire stacktrace: #5387

[keyboardDrummer]

Still occurs: https://github.com/dafny-lang/dafny/actions/runs/10417507125/job/28851913718?pr=5695

[keyboardDrummer]

Now we have the stacktrace, so maybe we can fix it:

   at System.Collections.Generic.Dictionary`2.Enumerator.MoveNext()
   at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
   at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector)
   at Microsoft.Dafny.DafnyOptions..ctor(DafnyOptions src, Boolean useNullWriters) in /Users/runner/work/dafny/dafny/dafny/Source/DafnyCore/DafnyOptions.cs:line 447
   at Microsoft.Dafny.Parser..ctor(DafnyOptions options, Scanner scanner, Errors errors, CancellationToken cancellationToken) in /Users/runner/work/dafny/dafny/dafny/Source/DafnyCore/AST/Grammar/ParserNonGeneratedPart.cs:line 24
   at Microsoft.Dafny.ProgramParser.SetupParser(String s, Uri uri, ErrorReporter errorReporter, CancellationToken cancellationToken) in /Users/runner/work/dafny/dafny/dafny/Source/DafnyCore/AST/Grammar/ProgramParser.cs:line 307
   at Microsoft.Dafny.ProgramParser.ParseFile(DafnyOptions options, String content, Uri uri, CancellationToken cancellationToken) in /Users/runner/work/dafny/dafny/dafny/Source/DafnyCore/AST/Grammar/ProgramParser.cs:line 281
   at Microsoft.Dafny.ProgramParser.ParseFile(DafnyOptions options, Func`1 getReader, Uri uri, CancellationToken cancellationToken) in /Users/runner/work/dafny/dafny/dafny/Source/DafnyCore/AST/Grammar/ProgramParser.cs:line 270
   at Microsoft.Dafny.LanguageServer.Language.CachingParser.ParseFile(DafnyOptions options, Func`1 getReader, Uri uri, CancellationToken cancellationToken) in /Users/runner/work/dafny/dafny/dafny/Source/DafnyLanguageServer/Language/CachingParser.cs:line 42
   at Microsoft.Dafny.ProgramParser.ParseFileWithErrorHandling(DafnyOptions options, Func`1 getContent, IToken origin, Uri uri, CancellationToken cancellationToken) in /Users/runner/work/dafny/dafny/dafny/Source/DafnyCore/AST/Grammar/ProgramParser.cs:line 115
  Stack Trace:
     at XunitAssertMessages.AssertM.WithMessage(String message, Action action)
   at XunitAssertMessages.AssertM.Equal(String expected, String actual, String userMessage)