Simplify fix

jack-williams · jack-williams · commit c691df968c53 · 2020-01-08T16:35:25.000Z
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -15863,7 +15863,10 @@ namespace ts {
                             }
                         }
                     }
-                    if (unionParent && !result) {
+                    if (unionParent && !result && targetIsOptional) {
+                        result = isRelatedTo(source, undefinedType);
+                    }
+                    if (unionParent && !result && source.flags & TypeFlags.Union) {
                         // The easiest way to get the right errors here is to un-defer (which may be costly)
                         // If it turns out this is too costly too often, we can replicate the error handling logic within
                         // typeRelatedToSomeType without the discriminatable type branch (as that requires a manifest union

Original file line number	Diff line number	Diff line change
`@@ -15863,7 +15863,10 @@ namespace ts {`
`15863`	`15863`	`}`
`15864`	`15864`	`}`
`15865`	`15865`	`}`
`15866`		`- if (unionParent && !result) {`
	`15866`	`+ if (unionParent && !result && targetIsOptional) {`
	`15867`	`+ result = isRelatedTo(source, undefinedType);`
	`15868`	`+ }`
	`15869`	`+ if (unionParent && !result && source.flags & TypeFlags.Union) {`
`15867`	`15870`	`// The easiest way to get the right errors here is to un-defer (which may be costly)`
`15868`	`15871`	`// If it turns out this is too costly too often, we can replicate the error handling logic within`
`15869`	`15872`	`// typeRelatedToSomeType without the discriminatable type branch (as that requires a manifest union`