fix some incorrect assumptions about the structure of properties

e.g., a C# getter body doesn't necessarily have Statements, and if it
does, it may have zero or more than one

src/EditorFeatures/CSharp/UseAutoProperty/UseAutoPropertyAnalyzer.cs

@@ -7,6 +7,7 @@
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Diagnostics;
 using Microsoft.CodeAnalysis.UseAutoProperty;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Editor.CSharp.UseAutoProperty
 {
@@ -81,11 +82,16 @@ private bool CheckExpressionSyntactically(ExpressionSyntax expression)
         protected override ExpressionSyntax GetGetterExpression(IMethodSymbol getMethod, CancellationToken cancellationToken)
         {
             var getAccessor = getMethod.DeclaringSyntaxReferences[0].GetSyntax(cancellationToken) as AccessorDeclarationSyntax;
-            var firstStatement = getAccessor?.Body?.Statements.SingleOrDefault();
-            if (firstStatement?.Kind() == SyntaxKind.ReturnStatement)
+            var statements = getAccessor?.Body?.Statements;
+            if (statements?.Count == 1)
             {
-                var expr = ((ReturnStatementSyntax)firstStatement).Expression;
-                return CheckExpressionSyntactically(expr) ? expr : null;
+                // this only works with a getter body with exactly one statement
+                var firstStatement = statements.Value[0];
+                if (firstStatement.Kind() == SyntaxKind.ReturnStatement)
+                {
+                    var expr = ((ReturnStatementSyntax)firstStatement).Expression;
+                    return CheckExpressionSyntactically(expr) ? expr : null;
+                }
             }
 
             return null;

src/EditorFeatures/VisualBasic/UseAutoProperty/UseAutoPropertyAnalyzer.vb

@@ -46,10 +46,14 @@ Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.UseAutoProperty
 
         Protected Overrides Function GetGetterExpression(getMethod As IMethodSymbol, cancellationToken As CancellationToken) As ExpressionSyntax
             Dim accessor = TryCast(TryCast(getMethod.DeclaringSyntaxReferences(0).GetSyntax(cancellationToken), AccessorStatementSyntax)?.Parent, AccessorBlockSyntax)
-            Dim firstStatement = accessor?.Statements.SingleOrDefault()
-            If firstStatement?.Kind() = SyntaxKind.ReturnStatement Then
-                Dim expr = DirectCast(firstStatement, ReturnStatementSyntax).Expression
-                Return If(CheckExpressionSyntactically(expr), expr, Nothing)
+            Dim statements = accessor?.Statements
+            If statements?.Count = 1 Then
+                ' this only works with a getter body with exactly one statement
+                Dim firstStatement = statements.Value(0)
+                If firstStatement.Kind() = SyntaxKind.ReturnStatement Then
+                    Dim expr = DirectCast(firstStatement, ReturnStatementSyntax).Expression
+                    Return If(CheckExpressionSyntactically(expr), expr, Nothing)
+                End If
             End If
 
             Return Nothing