USFM Parsing Bug: 'Stack Empty'

[Enkidu93]

Last month we had some Serval builds faulted with the error 'Stack empty' coming from the USFM parsing. See this doc for more information on the build.

[pmachapman]

This error occurs on Serval QA, and I was able to recreate it using the following USFM:

\id LJE - My Test Project
\h
\mt
\c 1
\p \v 0
\s
\p \v 1 \v 2 \v 3 \v 4 \v 5 \v 6 \v 7

[pmachapman]

I have also had this issue occur with the \zimagecopyrights USFM tag (used to auto-generate copyright credits for images in PtxPrint) when it is in present in front-matter, i.e A0FRTTEA.SFM:

\id FRT - Test English Apocrypha
\mt1 Test English Apocrypha
\pc Copyright Statement \zimagecopyrights
\pc Further copyright statements

This specific crash didn't occur using the version of machine on Serval prod (should this be logged as a separate issue as although it is the same error, it is a different cause?).

Here is the stack trace:

      System.InvalidOperationException: An error occurred while parsing the text 'FRT' in project 'GSTBT'. Verse: FRT 1:0, line: 16, character: 1, error: 'Stack empty.'
       ---> System.InvalidOperationException: Stack empty.
         at System.Collections.Generic.Stack`1.ThrowForEmptyStack()
         at System.Collections.Generic.Stack`1.Pop()
         at SIL.Machine.Corpora.ScriptureRefUsfmParserHandlerBase.NextElement(String marker)
         at SIL.Machine.Corpora.ScriptureRefUsfmParserHandlerBase.StartParentElement(String marker)
         at SIL.Machine.Corpora.UsfmTextBase.TextRowCollector.StartPara(UsfmParserState state, String marker, Boolean unknown, IReadOnlyList`1 attributes)
         at SIL.Machine.Corpora.UsfmParser.ProcessToken()
         at SIL.Machine.Corpora.UsfmTextBase.GetVersesInDocOrder()
         --- End of inner exception stack trace ---
         at SIL.Machine.Corpora.UsfmTextBase.GetVersesInDocOrder()
         at SIL.Machine.Corpora.ScriptureText.GetRows()
         at System.Linq.Enumerable.SelectManySingleSelectorIterator`2.MoveNext()
         at SIL.Machine.Corpora.TextCorpusEnumerator.MoveNext()
         at SIL.Machine.Corpora.NParallelTextCorpus.GetRows(IList`1 enumerators)+MoveNext()
         at SIL.Machine.Corpora.NParallelTextCorpus.GetRows(IEnumerable`1 textIds)+MoveNext()
         at SIL.Machine.Corpora.MergedTextCorpus.GetRows(IEnumerable`1 textIds)+MoveNext()
         at System.Linq.Enumerable.WhereIterator[TSource](IEnumerable`1 source, Func`3 predicate)+MoveNext()
         at SIL.Machine.Corpora.TextCorpusEnumerator.MoveNext()
         at SIL.Machine.Corpora.NParallelTextCorpus.GetRows(IList`1 enumerators)+MoveNext()
         at SIL.Machine.Corpora.NParallelTextCorpus.GetRows(IEnumerable`1 textIds)+MoveNext()
         at SIL.Machine.Corpora.ParallelTextCorpus.GetRows(IEnumerable`1 textIds)+MoveNext()
         at System.Collections.Generic.LargeArrayBuilder`1.AddRange(IEnumerable`1 items)
         at System.Collections.Generic.EnumerableHelpers.ToArray[T](IEnumerable`1 source)
         at SIL.ServiceToolkit.Services.ParallelCorpusPreprocessingService.PreprocessAsync(IReadOnlyList`1 corpora, Func`2 train, Func`4 inference, Boolean useKeyTerms) in /app/src/ServiceToolkit/src/SIL.ServiceToolkit/Services/ParallelCorpusPreprocessingService.cs:line 88
         at Serval.Machine.Shared.Services.TranslationPreprocessBuildJob.WriteDataFilesAsync(String buildId, IReadOnlyList`1 corpora, String buildOptions, CancellationToken cancellationToken) in /app/src/Machine/src/Serval.Machine.Shared/Services/TranslationPreprocessBuildJob.cs:line 47
         at Serval.Machine.Shared.Services.TranslationPreprocessBuildJob.WriteDataFilesAsync(String buildId, IReadOnlyList`1 corpora, String buildOptions, CancellationToken cancellationToken)
         at Serval.Machine.Shared.Services.TranslationPreprocessBuildJob.WriteDataFilesAsync(String buildId, IReadOnlyList`1 corpora, String buildOptions, CancellationToken cancellationToken)
         at Serval.Machine.Shared.Services.TranslationPreprocessBuildJob.WriteDataFilesAsync(String buildId, IReadOnlyList`1 corpora, String buildOptions, CancellationToken cancellationToken)
         at Serval.Machine.Shared.Services.TranslationPreprocessBuildJob.WriteDataFilesAsync(String buildId, IReadOnlyList`1 corpora, String buildOptions, CancellationToken cancellationToken)
         at Serval.Machine.Shared.Services.PreprocessBuildJob`1.DoWorkAsync(String engineId, String buildId, IReadOnlyList`1 data, String buildOptions, CancellationToken cancellationToken) in /app/src/Machine/src/Serval.Machine.Shared/Services/PreprocessBuildJob.cs:line 47
         at Serval.Machine.Shared.Services.HangfireBuildJob`2.RunAsync(String engineId, String buildId, TData data, String buildOptions, CancellationToken cancellationToken) in /app/src/Machine/src/Serval.Machine.Shared/Services/HangfireBuildJob.cs:line 56
         at Serval.Machine.Shared.Services.HangfireBuildJob`2.RunAsync(String engineId, String buildId, TData data, String buildOptions, CancellationToken cancellationToken) in /app/src/Machine/src/Serval.Machine.Shared/Services/HangfireBuildJob.cs:line 120
         at Serval.Machine.Shared.Services.HangfireBuildJob`2.RunAsync(String engineId, String buildId, TData data, String buildOptions, CancellationToken cancellationToken) in /app/src/Machine/src/Serval.Machine.Shared/Services/HangfireBuildJob.cs:line 124
         at InvokeStub_TaskAwaiter.GetResult(Object, Object, IntPtr*)
         at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

@Enkidu93 I think this is a blocker for Serval 1.10?