Only perform fallback when computed type is not an intersection or union

jack-williams · jack-williams · commit e91ee148cdcc · 2019-03-26T19:11:13.000Z
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -16184,7 +16184,10 @@ namespace ts {
                 }
                 let propType;
                 return isMatchingReference(reference, expr.expression) &&
-                    (isDiscriminantProperty(computedType, name) || (propType = getTypeOfPropertyOfType(computedType, name)) && isUnitType(propType));
+                (isDiscriminantProperty(computedType, name) ||
+                 ((computedType.flags & TypeFlags.UnionOrIntersection) === 0) &&
+                 (propType = getTypeOfPropertyOfType(computedType, name))
+                 && isUnitType(propType));
             }
 
             function narrowTypeByDiscriminant(type: Type, access: AccessExpression, narrowType: (t: Type) => Type): Type {

Original file line number	Diff line number	Diff line change
`@@ -16184,7 +16184,10 @@ namespace ts {`
`16184`	`16184`	`}`
`16185`	`16185`	`let propType;`
`16186`	`16186`	`return isMatchingReference(reference, expr.expression) &&`
`16187`		`- (isDiscriminantProperty(computedType, name) \|\| (propType = getTypeOfPropertyOfType(computedType, name)) && isUnitType(propType));`
	`16187`	`+ (isDiscriminantProperty(computedType, name) \|\|`
	`16188`	`+ ((computedType.flags & TypeFlags.UnionOrIntersection) === 0) &&`
	`16189`	`+ (propType = getTypeOfPropertyOfType(computedType, name))`
	`16190`	`+ && isUnitType(propType));`
`16188`	`16191`	`}`
`16189`	`16192`
`16190`	`16193`	`function narrowTypeByDiscriminant(type: Type, access: AccessExpression, narrowType: (t: Type) => Type): Type {`