Remove only undefined, not null | undefined, from declared type

sandersn · sandersn · commit 36513f21aba6 · 2017-03-07T09:14:51.000-08:00
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -10929,7 +10929,7 @@ namespace ts {
                 declaration.initializer &&
                 getFalsyFlags(declaredType) & TypeFlags.Undefined &&
                 !(getFalsyFlags(checkExpression(declaration.initializer)) & TypeFlags.Undefined);
-            return annotationIncludesUndefined ? getNonNullableType(declaredType) : declaredType;
+            return annotationIncludesUndefined ? getTypeWithFacts(declaredType, TypeFacts.NEUndefined) : declaredType;
         }
 
         function checkIdentifier(node: Identifier): Type {
diff --git a/tests/cases/compiler/defaultParameterAddsUndefinedWithStrictNullChecks.ts b/tests/cases/compiler/defaultParameterAddsUndefinedWithStrictNullChecks.ts
@@ -27,6 +27,13 @@ function foo4(x: string | undefined = undefined, b: number) {
     x = undefined;
 }
 
+type OptionalNullableString = string | null | undefined;
+function allowsNull(val: OptionalNullableString = "") {
+    val = null;
+    val = 'string and null are both ok';
+}
+allowsNull(null); // still allows passing null
+
 
 
 // .d.ts should have `string | undefined` for foo1, foo2, foo3 and foo4

Original file line number	Diff line number	Diff line change
`@@ -10929,7 +10929,7 @@ namespace ts {`
`10929`	`10929`	`declaration.initializer &&`
`10930`	`10930`	`getFalsyFlags(declaredType) & TypeFlags.Undefined &&`
`10931`	`10931`	`!(getFalsyFlags(checkExpression(declaration.initializer)) & TypeFlags.Undefined);`
`10932`		`- return annotationIncludesUndefined ? getNonNullableType(declaredType) : declaredType;`
	`10932`	`+ return annotationIncludesUndefined ? getTypeWithFacts(declaredType, TypeFacts.NEUndefined) : declaredType;`
`10933`	`10933`	`}`
`10934`	`10934`
`10935`	`10935`	`function checkIdentifier(node: Identifier): Type {`