Match control flow logic for switch statements to conditional expressions

Author: ahejlsberg

src/compiler/checker.ts

@@ -15780,9 +15780,6 @@ namespace ts {
 
             function getTypeAtSwitchClause(flow: FlowSwitchClause): FlowType {
                 const expr = flow.switchStatement.expression;
-                if (containsMatchingReferenceDiscriminant(reference, expr)) {
-                    return declaredType;
-                }
                 const flowType = getTypeAtFlowNode(flow.antecedent);
                 let type = getTypeFromFlowType(flowType);
                 if (isMatchingReference(reference, expr)) {
@@ -15797,6 +15794,9 @@ namespace ts {
                 else if (expr.kind === SyntaxKind.TypeOfExpression && isMatchingReference(reference, (expr as TypeOfExpression).expression)) {
                     type = narrowBySwitchOnTypeOf(type, flow.switchStatement, flow.clauseStart, flow.clauseEnd);
                 }
+                else if (containsMatchingReferenceDiscriminant(reference, expr)) {
+                    type = declaredType;
+                }
                 return createFlowType(type, isIncomplete(flowType));
             }