Use union type when binding element has initializer

ahejlsberg · ahejlsberg · commit a25104e152dc · 2016-08-27T09:40:49.000-07:00
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -2974,7 +2974,9 @@ namespace ts {
             if (strictNullChecks && declaration.initializer && !(getFalsyFlags(checkExpressionCached(declaration.initializer)) & TypeFlags.Undefined)) {
                 type = getTypeWithFacts(type, TypeFacts.NEUndefined);
             }
-            return type;
+            return declaration.initializer ?
+                getUnionType([type, checkExpressionCached(declaration.initializer)], /*subtypeReduction*/ true) :
+                type;
         }
 
         function getTypeForVariableLikeDeclarationFromJSDocComment(declaration: VariableLikeDeclaration) {

Original file line number	Diff line number	Diff line change
`@@ -2974,7 +2974,9 @@ namespace ts {`
`2974`	`2974`	`if (strictNullChecks && declaration.initializer && !(getFalsyFlags(checkExpressionCached(declaration.initializer)) & TypeFlags.Undefined)) {`
`2975`	`2975`	`type = getTypeWithFacts(type, TypeFacts.NEUndefined);`
`2976`	`2976`	`}`
`2977`		`- return type;`
	`2977`	`+ return declaration.initializer ?`
	`2978`	`+ getUnionType([type, checkExpressionCached(declaration.initializer)], /subtypeReduction/ true) :`
	`2979`	`+ type;`
`2978`	`2980`	`}`
`2979`	`2981`
`2980`	`2982`	`function getTypeForVariableLikeDeclarationFromJSDocComment(declaration: VariableLikeDeclaration) {`