Merge pull request #13933 from gafter/dev15-preview-5-13884

Avoid a null value key in the decision tree in error recovery situations.

src/Compilers/CSharp/Portable/BoundTree/DecisionTree.cs

@@ -224,7 +224,7 @@ private void AddToDecisionTree(DecisionTree decisionTree, BoundPatternSwitchLabe
                 case BoundKind.ConstantPattern:
                     {
                         var constantPattern = (BoundConstantPattern)pattern;
-                        AddByValue(decisionTree, constantPattern.Value, (e, t) => new DecisionTree.Guarded(e, t, default(ImmutableArray<KeyValuePair<BoundExpression, LocalSymbol>>), _section, guard, label), label.HasErrors);
+                        AddByValue(decisionTree, constantPattern.Value, (e, t) => new DecisionTree.Guarded(e, t, default(ImmutableArray<KeyValuePair<BoundExpression, LocalSymbol>>), _section, guard, label));
                         break;
                     }
                 case BoundKind.DeclarationPattern:
@@ -475,7 +475,7 @@ private ErrorCode CheckSubsumed(BoundPattern pattern, DecisionTree decisionTree,
             BoundExpression expression,
             TypeSymbol type);
 
-        private DecisionTree AddByValue(DecisionTree decision, BoundExpression value, DecisionMaker makeDecision, bool hasErrors)
+        private DecisionTree AddByValue(DecisionTree decision, BoundExpression value, DecisionMaker makeDecision)
         {
             if (decision.MatchIsComplete)
             {
@@ -487,17 +487,17 @@ private DecisionTree AddByValue(DecisionTree decision, BoundExpression value, De
             switch (decision.Kind)
             {
                 case DecisionTree.DecisionKind.ByType:
-                    return AddByValue((DecisionTree.ByType)decision, value, makeDecision, hasErrors);
+                    return AddByValue((DecisionTree.ByType)decision, value, makeDecision);
                 case DecisionTree.DecisionKind.ByValue:
-                    return AddByValue((DecisionTree.ByValue)decision, value, makeDecision, hasErrors);
+                    return AddByValue((DecisionTree.ByValue)decision, value, makeDecision);
                 case DecisionTree.DecisionKind.Guarded:
-                    return AddByValue((DecisionTree.Guarded)decision, value, makeDecision, hasErrors);
+                    return AddByValue((DecisionTree.Guarded)decision, value, makeDecision);
                 default:
                     throw ExceptionUtilities.UnexpectedValue(decision.Kind);
             }
         }
 
-        private DecisionTree AddByValue(DecisionTree.Guarded guarded, BoundExpression value, DecisionMaker makeDecision, bool hasErrors)
+        private DecisionTree AddByValue(DecisionTree.Guarded guarded, BoundExpression value, DecisionMaker makeDecision)
         {
             if (guarded.Default != null)
             {
@@ -511,20 +511,20 @@ private DecisionTree AddByValue(DecisionTree.Guarded guarded, BoundExpression va
                 guarded.Default = new DecisionTree.ByValue(guarded.Expression, guarded.Type, null);
             }
 
-            return AddByValue(guarded.Default, value, makeDecision, hasErrors);
+            return AddByValue(guarded.Default, value, makeDecision);
         }
 
-        private DecisionTree AddByValue(DecisionTree.ByValue byValue, BoundExpression value, DecisionMaker makeDecision, bool hasErrors)
+        private DecisionTree AddByValue(DecisionTree.ByValue byValue, BoundExpression value, DecisionMaker makeDecision)
         {
             Debug.Assert(value.Type == byValue.Type);
             if (byValue.Default != null)
             {
-                return AddByValue(byValue.Default, value, makeDecision, hasErrors);
+                return AddByValue(byValue.Default, value, makeDecision);
             }
 
             // For error recovery, to avoid "unreachable code" diagnostics when there is a bad case
             // label, we use the case label itself as the value key.
-            object valueKey = hasErrors ? (object)value : value.ConstantValue.Value;
+            object valueKey = value.ConstantValue?.Value ?? value;
             DecisionTree valueDecision;
             if (byValue.ValueAndDecision.TryGetValue(valueKey, out valueDecision))
             {
@@ -546,13 +546,13 @@ private DecisionTree AddByValue(DecisionTree.ByValue byValue, BoundExpression va
             return valueDecision;
         }
 
-        private DecisionTree AddByValue(DecisionTree.ByType byType, BoundExpression value, DecisionMaker makeDecision, bool hasErrors)
+        private DecisionTree AddByValue(DecisionTree.ByType byType, BoundExpression value, DecisionMaker makeDecision)
         {
             if (byType.Default != null)
             {
                 try
                 {
-                    return AddByValue(byType.Default, value, makeDecision, hasErrors);
+                    return AddByValue(byType.Default, value, makeDecision);
                 }
                 finally
                 {
@@ -619,7 +619,7 @@ private DecisionTree AddByValue(DecisionTree.ByType byType, BoundExpression valu
                 byType.TypeAndDecision.Add(new KeyValuePair<TypeSymbol, DecisionTree>(value.Type, forType));
             }
 
-            return AddByValue(forType, value, makeDecision, hasErrors);
+            return AddByValue(forType, value, makeDecision);
         }
 
         private DecisionTree AddByType(DecisionTree decision, TypeSymbol type, DecisionMaker makeDecision)