CSharpDecompiler: EnumValueDisplayMode does not expect Class, sets to null and throws (ProtoContract issue?)

[StalkR]

I noticed since version 8.0.0.7106-preview2 up to current master, ilspycmd fails to decompile, complaining about ArgumentOutOfRangeException in CSharpDecompiler.cs:1432 (full stacktrace at the end). It works fine up to version 8.0.0.7007-preview1 then starts crashing.

Just 10 commits between these tags for this file:

$ git log v8.0-preview1..v8.0-preview2 ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs | grep ^commit | wc -l
10

I can share the dll privately if necessary, but the code is basically:

namespace SomeNamespace
{
        public class SomeClass
	{
		[ProtoContract]
		public enum SomeEnum
		{
			Zero,
			One
		}
	}
}

I can reproduce with ILSpy as well, it just fails to decompile this specific enum.

Debugging a bit, it's not expecting decompileRun.EnumValueDisplayMode to be null, coming from this:

				decompileRun.EnumValueDisplayMode = typeDef.Kind == TypeKind.Enum
					? DetectBestEnumValueDisplayMode(typeDef, module.PEFile)
					: null;

In this situation, typeDef.Kind is actually Class.

If I replace null with EnumValueDisplayMode.None for instance, it's able to decompile.

Did you set it on purpose to null to catch this sort of situations and investigate closer? otherwise I can send you this pull request always setting it to EnumValueDisplayMode.None as safe fallback value.

With that exception out of the way, decompilation gives:

[ProtoContract]
public enum SomeEnum
{
	private class SomeNamespace_SomeClass<>SomeEnum<>Actor : IActivator, IActivator<SomeEnum>
	{
		private virtual sealed object CreateInstance()
		{
			return default(SomeEnum);
		}

		object IActivator.CreateInstance()
		{
			//ILSpy generated this explicit interface implementation from .override directive in CreateInstance
			return this.CreateInstance();
		}

		private virtual sealed SomeEnumCreateInstance()
		{
			//IL_000f: Expected I4, but got O
			return (MyLayerMode)(object)default(SomeEnum);
		}

		SomeEnumIActivator<SomeEnum>.CreateInstance()
		{
			//ILSpy generated this explicit interface implementation from .override directive in CreateInstance
			return this.CreateInstance();
		}
	}
	,
	Zero,
	One
}

But I think it shouldn't show this class at all, just the fields.

Maybe this extra class comes from the [ProtoContract] annotation? (protobuf-net most likely)

Thanks for the project and maintaining it ❤️

Error message

System.AggregateException: One or more errors occurred. (Error decompiling @[redacted] [redacted])
 ---> Error decompiling @[redacted] [redacted] in assembly "[redacted]"
 ---> System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values.
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DoDecompile(ITypeDefinition typeDef, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in CSharpDecompiler.cs:line 1432
-- continuing with outer exception (ICSharpCode.Decompiler.DecompilerException) --
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DoDecompile(ITypeDefinition typeDef, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in CSharpDecompiler.cs:line 1440
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.<>c__DisplayClass74_0.<DoDecompile>g__DoDecompileMember|0(IEntity entity, RecordDecompiler recordDecompiler, PartialTypeInfo partialType) in CSharpDecompiler.cs:line 1491
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DoDecompile(ITypeDefinition typeDef, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in CSharpDecompiler.cs:line 1368
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DoDecompileTypes(IEnumerable`1 types, DecompileRun decompileRun, ITypeResolveContext decompilationContext, SyntaxTree syntaxTree) in CSharpDecompiler.cs:line 651
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DecompileTypes(IEnumerable`1 types) in CSharpDecompiler.cs:line 950
   at ICSharpCode.Decompiler.CSharp.ProjectDecompiler.WholeProjectDecompiler.<>c__DisplayClass46_0.<WriteCodeFilesInProject>b__5(IGrouping`2 file) in WholeProjectDecompiler.cs:line 274
   at System.Threading.Tasks.Parallel.<>c__DisplayClass44_0`2.<PartitionerForEachWorker>b__1(IEnumerator& partitionState, Int32 timeout, Boolean& replicationDelegateYieldedBeforeCompletion) in offset 259
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() in offset 17
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw(Exception source) in offset 0
   at System.Threading.Tasks.Parallel.<>c__DisplayClass44_0`2.<PartitionerForEachWorker>b__1(IEnumerator& partitionState, Int32 timeout, Boolean& replicationDelegateYieldedBeforeCompletion) in offset 609
   at System.Threading.Tasks.TaskReplicator.Replica`1.ExecuteAction(Boolean& yieldedBeforeCompletion) in offset 0
   at System.Threading.Tasks.TaskReplicator.Replica.Execute() in offset 0
   --- End of inner exception stack trace ---
   at System.Threading.Tasks.TaskReplicator.Run[TState](ReplicatableUserAction`1 action, ParallelOptions options, Boolean stopOnFirstFailure)
   at System.Threading.Tasks.Parallel.PartitionerForEachWorker[TSource,TLocal](Partitioner`1 source, ParallelOptions parallelOptions, Action`1 simpleBody, Action`2 bodyWithState, Action`3 bodyWithStateAndIndex, Func`4 bodyWithStateAndLocal, Func`5 bodyWithEverything, Func`1 localInit, Action`1 localFinally)
--- End of stack trace from previous location ---
   at System.Threading.Tasks.Parallel.ThrowSingleCancellationExceptionOrOtherException(ICollection exceptions, CancellationToken cancelToken, Exception otherException)
   at System.Threading.Tasks.Parallel.PartitionerForEachWorker[TSource,TLocal](Partitioner`1 source, ParallelOptions parallelOptions, Action`1 simpleBody, Action`2 bodyWithState, Action`3 bodyWithStateAndIndex, Func`4 bodyWithStateAndLocal, Func`5 bodyWithEverything, Func`1 localInit, Action`1 localFinally)
   at System.Threading.Tasks.Parallel.ForEach[TSource](Partitioner`1 source, ParallelOptions parallelOptions, Action`1 body)
   at ICSharpCode.Decompiler.CSharp.ProjectDecompiler.WholeProjectDecompiler.<>c__DisplayClass46_0.<WriteCodeFilesInProject>g__ProcessFiles|3(List`1 files) in /_/ICSharpCode.Decompiler/CSharp/ProjectDecompiler/WholeProjectDecompiler.cs:line 255
   at ICSharpCode.Decompiler.CSharp.ProjectDecompiler.WholeProjectDecompiler.WriteCodeFilesInProject(PEFile module, IList`1 partialTypes, CancellationToken cancellationToken) in /_/ICSharpCode.Decompiler/CSharp/ProjectDecompiler/WholeProjectDecompiler.cs:line 221
   at ICSharpCode.Decompiler.CSharp.ProjectDecompiler.WholeProjectDecompiler.DecompileProject(PEFile moduleDefinition, String targetDirectory, TextWriter projectFileWriter, CancellationToken cancellationToken) in /_/ICSharpCode.Decompiler/CSharp/ProjectDecompiler/WholeProjectDecompiler.cs:line 154
   at ICSharpCode.ILSpyCmd.ILSpyCmdProgram.DecompileAsProject(String assemblyFileName, String projectFileName) in D:\a\ILSpy\ILSpy\ICSharpCode.ILSpyCmd\IlspyCmdProgram.cs:line 318
   at ICSharpCode.ILSpyCmd.ILSpyCmdProgram.OnExecuteAsync(CommandLineApplication app) in D:\a\ILSpy\ILSpy\ICSharpCode.ILSpyCmd\IlspyCmdProgram.cs:line 147

[siegfriedpammer]

I have a hard time reproducing the exact issue. Would you be able to provide the assembly in question? Thanks!

[StalkR]

Thanks much!