Unexpected value 'UnsetConversionKind'

[jnyrup]

Version Used:
Visual Studio 16.1.0 Preview 1.0

Steps to Reproduce:
I don't have an exact case as the crash happened during rewriting some code and I haven't been able to reproduce it yet.
The code was somewhat similar to:

var a = new List<int>();
var b = new List<int>();

foreach ((int x, int y, int z) in
    a.Zip(
    b.Join(b,
            e => e,
            e => e,
            (s, t) => (s, t)),
    (f, g) => (f, g.s, g.t)))
{
}

Expected Behavior:
No exception.

Actual Behavior:

System.InvalidOperationException : Unexpected value 'UnsetConversionKind' of type 'Microsoft.CodeAnalysis.CSharp.ConversionKind'
   at Microsoft.CodeAnalysis.CSharp.ConversionKindExtensions.IsImplicitConversion(ConversionKind conversionKind)
   at Microsoft.CodeAnalysis.CSharp.Conversion.get_IsExplicit()
   at Microsoft.CodeAnalysis.CSharp.Utilities.SpeculationAnalyzer.ConversionsAreCompatible(Conversion originalConversion,Conversion newConversion)
   at Microsoft.CodeAnalysis.CSharp.Utilities.SpeculationAnalyzer.ForEachConversionsAreCompatible(SemanticModel originalModel,CommonForEachStatementSyntax originalForEach,SemanticModel newModel,CommonForEachStatementSyntax newForEach)
   at Microsoft.CodeAnalysis.Shared.Utilities.AbstractSpeculationAnalyzer`7.ReplacementBreaksForEachStatement(TForEachStatementSyntax forEachStatement,TForEachStatementSyntax newForEachStatement)
   at Microsoft.CodeAnalysis.Shared.Utilities.AbstractSpeculationAnalyzer`7.ReplacementChangesSemanticsForNode(SyntaxNode currentOriginalNode,SyntaxNode currentReplacedNode,SyntaxNode previousOriginalNode,SyntaxNode previousReplacedNode)
   at Microsoft.CodeAnalysis.Shared.Utilities.AbstractSpeculationAnalyzer`7.ReplacementChangesSemantics(SyntaxNode currentOriginalNode,SyntaxNode currentReplacedNode,SyntaxNode originalRoot,Boolean skipVerificationForCurrentNode)
   at Microsoft.CodeAnalysis.Shared.Utilities.AbstractSpeculationAnalyzer`7.ReplacementChangesSemantics()
   at Microsoft.CodeAnalysis.CSharp.Extensions.ExpressionSyntaxExtensions.CanReplaceWithReducedName(NameSyntax name,TypeSyntax reducedName,SemanticModel semanticModel,CancellationToken cancellationToken)
   at Microsoft.CodeAnalysis.CSharp.Extensions.ExpressionSyntaxExtensions.TryReduce(NameSyntax name,SemanticModel semanticModel,TypeSyntax& replacementNode,TextSpan& issueSpan,OptionSet optionSet,CancellationToken cancellationToken)
   at Microsoft.CodeAnalysis.CSharp.Extensions.ExpressionSyntaxExtensions.TryReduceExplicitName(ExpressionSyntax expression,SemanticModel semanticModel,TypeSyntax& replacementNode,TextSpan& issueSpan,OptionSet optionSet,CancellationToken cancellationToken)
   at Microsoft.CodeAnalysis.CSharp.Extensions.ExpressionSyntaxExtensions.TryReduceOrSimplifyExplicitName(ExpressionSyntax expression,SemanticModel semanticModel,ExpressionSyntax& replacementNode,TextSpan& issueSpan,OptionSet optionSet,CancellationToken cancellationToken)
   at Microsoft.CodeAnalysis.CSharp.Simplification.CSharpNameReducer.SimplifyName(SyntaxNode node,SemanticModel semanticModel,OptionSet optionSet,CancellationToken cancellationToken)
   at Microsoft.CodeAnalysis.CSharp.Simplification.AbstractCSharpReducer.AbstractReductionRewriter.SimplifyNode[TNode](TNode node,SyntaxNode newNode,SyntaxNode parentNode,Func`5 simplifier)
   at Microsoft.CodeAnalysis.CSharp.Simplification.AbstractCSharpReducer.AbstractReductionRewriter.SimplifyExpression[TExpression](TExpression expression,SyntaxNode newNode,Func`5 simplifier)
   at Microsoft.CodeAnalysis.CSharp.Simplification.CSharpNameReducer.Rewriter.VisitAliasQualifiedName(AliasQualifiedNameSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.AliasQualifiedNameSyntax.Accept[TResult](CSharpSyntaxVisitor`1 visitor)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitMemberAccessExpression(MemberAccessExpressionSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Simplification.CSharpNameReducer.Rewriter.VisitMemberAccessExpression(MemberAccessExpressionSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.MemberAccessExpressionSyntax.Accept[TResult](CSharpSyntaxVisitor`1 visitor)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitMemberAccessExpression(MemberAccessExpressionSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Simplification.CSharpNameReducer.Rewriter.VisitMemberAccessExpression(MemberAccessExpressionSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.MemberAccessExpressionSyntax.Accept[TResult](CSharpSyntaxVisitor`1 visitor)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.Simplification.AbstractCSharpReducer.AbstractReductionRewriter.VisitInvocationExpression(InvocationExpressionSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.InvocationExpressionSyntax.Accept[TResult](CSharpSyntaxVisitor`1 visitor)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitArgument(ArgumentSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.ArgumentSyntax.Accept[TResult](CSharpSyntaxVisitor`1 visitor)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitListElement[TNode](TNode node)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitList[TNode](SeparatedSyntaxList`1 list)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitArgumentList(ArgumentListSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.ArgumentListSyntax.Accept[TResult](CSharpSyntaxVisitor`1 visitor)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.Simplification.AbstractCSharpReducer.AbstractReductionRewriter.VisitInvocationExpression(InvocationExpressionSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.InvocationExpressionSyntax.Accept[TResult](CSharpSyntaxVisitor`1 visitor)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitForEachVariableStatement(ForEachVariableStatementSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.ForEachVariableStatementSyntax.Accept[TResult](CSharpSyntaxVisitor`1 visitor)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.Simplification.AbstractCSharpReducer.AbstractReductionRewriter.VisitNodeOrToken(SyntaxNodeOrToken nodeOrToken,SemanticModel semanticModel,Boolean simplifyAllDescendants)
   at async Microsoft.CodeAnalysis.Simplification.AbstractSimplificationService`3.<>c__DisplayClass10_1.<ReduceAsync>b__0[TExpressionSyntax,TStatementSyntax,TCrefSyntax](<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Simplification.AbstractSimplificationService`3.ReduceAsyncInternal[TExpressionSyntax,TStatementSyntax,TCrefSyntax](<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Simplification.AbstractSimplificationService`3.ReduceAsync[TExpressionSyntax,TStatementSyntax,TCrefSyntax](<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Simplification.Simplifier.ReduceAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.ExtractMethod.MethodExtractor.CodeGenerator`3.GenerateAsync[TStatement,TExpression,TNodeUnderContainer](<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.ExtractMethod.MethodExtractor.ExtractMethodAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.ExtractMethod.AbstractExtractMethodService`3.ExtractMethodAsync[TValidator,TExtractor,TResult](<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeRefactorings.ExtractMethod.ExtractMethodCodeRefactoringProvider.GetCodeActionAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeRefactorings.ExtractMethod.ExtractMethodCodeRefactoringProvider.ComputeRefactoringsAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeRefactorings.CodeRefactoringService.GetRefactoringFromProviderAsync(<Unknown Parameters>)
   at Microsoft.VisualStudio.Telemetry.WindowsErrorReporting.WatsonReport.GetClrWatsonExceptionInfo(Exception exceptionObject)

It looks like https://github.com/dotnet/roslyn/blob/master/src/Compilers/CSharp/Portable/Binder/Semantics/Conversions/ConversionKindExtensions.cs is missing a case for UnsetConversionKind after that enum was added in #33648.

[jinujoseph]

Duplicate of #34984