UnexpectedValue exception is thrown for scenario in Microsoft.CodeAnalysis.CSharp.UnitTests.DiagnosticTest.GetDiagnosticsCalledTwice unit-test

[AlekseyTs]

For the Microsoft.CodeAnalysis.CSharp.UnitTests.DiagnosticTest.GetDiagnosticsCalledTwice unit-test:

• Add

compilation.GetDiagnostics();
compilation.GetEmitDiagnostics();

right after creation of the compilation.

• Run the test

Observed UnexpectedValue exception is thrown during GetEmitDiagnostics call (doesn't repro without calling GetDiagnostics before it):

 	Microsoft.CodeAnalysis.dll!Roslyn.Utilities.ExceptionUtilities.UnexpectedValue(object o) Line 20	C#
>	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.IteratorRewriter.Rewrite(Microsoft.CodeAnalysis.CSharp.BoundStatement body, Microsoft.CodeAnalysis.CSharp.Symbols.MethodSymbol method, int methodOrdinal, Microsoft.CodeAnalysis.CodeGen.VariableSlotAllocator slotAllocatorOpt, Microsoft.CodeAnalysis.CSharp.TypeCompilationState compilationState, Microsoft.CodeAnalysis.DiagnosticBag diagnostics, out Microsoft.CodeAnalysis.CSharp.IteratorStateMachine stateMachineType) Line 73	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.LowerBodyOrInitializer(Microsoft.CodeAnalysis.CSharp.Symbols.MethodSymbol method, int methodOrdinal, Microsoft.CodeAnalysis.CSharp.BoundStatement body, Microsoft.CodeAnalysis.CSharp.SynthesizedSubmissionFields previousSubmissionFields, Microsoft.CodeAnalysis.CSharp.TypeCompilationState compilationState, bool instrumentForDynamicAnalysis, Microsoft.CodeAnalysis.CodeGen.DebugDocumentProvider debugDocumentProvider, ref System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.CodeGen.SourceSpan> dynamicAnalysisSpans, Microsoft.CodeAnalysis.DiagnosticBag diagnostics, ref Microsoft.CodeAnalysis.CodeGen.VariableSlotAllocator lazyVariableSlotAllocator, Microsoft.CodeAnalysis.PooledObjects.ArrayBuilder<Microsoft.CodeAnalysis.CodeGen.LambdaDebugInfo> lambdaDebugInfoBuilder, Microsoft.CodeAnalysis.PooledObjects.ArrayBuilder<Microsoft.CodeAnalysis.CodeGen.ClosureDebugInfo> closureDebugInfoBuilder, out Microsoft.CodeAnalysis.CSharp.StateMachineTypeSymbol stateMachineTypeOpt) Line 1380	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileMethod(Microsoft.CodeAnalysis.CSharp.Symbols.MethodSymbol methodSymbol, int methodOrdinal, ref Microsoft.CodeAnalysis.CSharp.Binder.ProcessedFieldInitializers processedInitializers, Microsoft.CodeAnalysis.CSharp.SynthesizedSubmissionFields previousSubmissionFields, Microsoft.CodeAnalysis.CSharp.TypeCompilationState compilationState) Line 1138	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileNamedType(Microsoft.CodeAnalysis.CSharp.Symbols.NamedTypeSymbol containingType) Line 518	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.VisitNamedType(Microsoft.CodeAnalysis.CSharp.Symbols.NamedTypeSymbol symbol, Microsoft.CodeAnalysis.CSharp.TypeCompilationState arg) Line 396	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.Symbols.NamedTypeSymbol.Accept<Microsoft.CodeAnalysis.CSharp.TypeCompilationState, object>(Microsoft.CodeAnalysis.CSharp.CSharpSymbolVisitor<Microsoft.CodeAnalysis.CSharp.TypeCompilationState, object> visitor, Microsoft.CodeAnalysis.CSharp.TypeCompilationState argument) Line 572	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileNamespace(Microsoft.CodeAnalysis.CSharp.Symbols.NamespaceSymbol symbol) Line 375	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileMethodBodies(Microsoft.CodeAnalysis.CSharp.CSharpCompilation compilation, Microsoft.CodeAnalysis.CSharp.Emit.PEModuleBuilder moduleBeingBuiltOpt, bool emittingPdb, bool emitTestCoverageData, bool hasDeclarationErrors, bool emitMethodBodies, Microsoft.CodeAnalysis.DiagnosticBag diagnostics, System.Predicate<Microsoft.CodeAnalysis.CSharp.Symbol> filterOpt, System.Threading.CancellationToken cancellationToken) Line 156	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.CSharpCompilation.CompileMethods(Microsoft.CodeAnalysis.Emit.CommonPEModuleBuilder moduleBuilder, bool emittingPdb, bool emitMetadataOnly, bool emitTestCoverageData, Microsoft.CodeAnalysis.DiagnosticBag diagnostics, System.Predicate<Microsoft.CodeAnalysis.Symbols.ISymbolInternal> filterOpt, System.Threading.CancellationToken cancellationToken) Line 2771	C#
 	Microsoft.CodeAnalysis.dll!Microsoft.CodeAnalysis.Compilation.Emit(System.IO.Stream peStream, System.IO.Stream metadataPEStream, System.IO.Stream pdbStream, System.IO.Stream xmlDocumentationStream, System.IO.Stream win32Resources, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.ResourceDescription> manifestResources, Microsoft.CodeAnalysis.Emit.EmitOptions options, Microsoft.CodeAnalysis.IMethodSymbol debugEntryPoint, System.IO.Stream sourceLinkStream, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.EmbeddedText> embeddedTexts, Microsoft.CodeAnalysis.CodeGen.CompilationTestData testData, System.Threading.CancellationToken cancellationToken) Line 2497	C#
 	Microsoft.CodeAnalysis.dll!Microsoft.CodeAnalysis.Compilation.Emit(System.IO.Stream peStream, System.IO.Stream pdbStream, System.IO.Stream xmlDocumentationStream, System.IO.Stream win32Resources, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.ResourceDescription> manifestResources, Microsoft.CodeAnalysis.Emit.EmitOptions options, Microsoft.CodeAnalysis.IMethodSymbol debugEntryPoint, System.IO.Stream sourceLinkStream, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.EmbeddedText> embeddedTexts, System.IO.Stream metadataPEStream, System.Threading.CancellationToken cancellationToken) Line 2441	C#
 	Roslyn.Test.Utilities.dll!Microsoft.CodeAnalysis.DiagnosticExtensions.GetEmitDiagnostics<Microsoft.CodeAnalysis.CSharp.CSharpCompilation>(Microsoft.CodeAnalysis.CSharp.CSharpCompilation c, Microsoft.CodeAnalysis.Emit.EmitOptions options, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.ResourceDescription> manifestResources) Line 376	C#
 	Roslyn.Test.Utilities.dll!Microsoft.CodeAnalysis.DiagnosticExtensions.GetEmitDiagnostics<Microsoft.CodeAnalysis.CSharp.CSharpCompilation>(Microsoft.CodeAnalysis.CSharp.CSharpCompilation c) Line 388	C#
 	Microsoft.CodeAnalysis.CSharp.Test.Utilities.dll!Microsoft.CodeAnalysis.CSharp.Test.Utilities.CSharpTestBase.VerifyUsedAssemblyReferences(System.Func<Microsoft.CodeAnalysis.CSharp.CSharpCompilation> createCompilationLambda) Line 1062	C#
 	Microsoft.CodeAnalysis.CSharp.Test.Utilities.dll!Microsoft.CodeAnalysis.CSharp.Test.Utilities.CSharpTestBase.CreateCompilationCore(Microsoft.CodeAnalysis.CSharp.Test.Utilities.CSharpTestSource source, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.MetadataReference> references, Microsoft.CodeAnalysis.CSharp.CSharpCompilationOptions options, Microsoft.CodeAnalysis.CSharp.CSharpParseOptions parseOptions, string assemblyName, string sourceFileName, bool skipUsesIsNullable, Microsoft.CodeAnalysis.CSharp.MessageID? experimentalFeature) Line 1051	C#
 	Microsoft.CodeAnalysis.CSharp.Test.Utilities.dll!Microsoft.CodeAnalysis.CSharp.Test.Utilities.CSharpTestBase.CreateEmptyCompilation(Microsoft.CodeAnalysis.CSharp.Test.Utilities.CSharpTestSource source, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.MetadataReference> references, Microsoft.CodeAnalysis.CSharp.CSharpCompilationOptions options, Microsoft.CodeAnalysis.CSharp.CSharpParseOptions parseOptions, string assemblyName, string sourceFileName, bool skipUsesIsNullable) Line 1009	C#
 	Microsoft.CodeAnalysis.CSharp.Test.Utilities.dll!Microsoft.CodeAnalysis.CSharp.Test.Utilities.CSharpTestBase.CreateCompilation(Microsoft.CodeAnalysis.CSharp.Test.Utilities.CSharpTestSource source, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.MetadataReference> references, Microsoft.CodeAnalysis.CSharp.CSharpCompilationOptions options, Microsoft.CodeAnalysis.CSharp.CSharpParseOptions parseOptions, Roslyn.Test.Utilities.TargetFramework targetFramework, string assemblyName, string sourceFileName, bool skipUsesIsNullable) Line 1000	C#
 	Microsoft.CodeAnalysis.CSharp.Syntax.UnitTests.dll!Microsoft.CodeAnalysis.CSharp.UnitTests.DiagnosticTest.GetDiagnosticsCalledTwice() Line 2245	C#