Telling left and right is hard, apparently

jack-williams · jack-williams · commit 61d2eaf5dc33 · 2019-03-27T15:51:09.000Z
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -16269,7 +16269,7 @@ namespace ts {
                         if (isMatchingReferenceDiscriminant(left, declaredType) || isMatchingInFlowDiscriminant(left, type)) {
                             return narrowTypeByDiscriminant(type, <AccessExpression>left, t => narrowTypeByEquality(t, operator, right, assumeTrue));
                         }
-                        if (isMatchingReferenceDiscriminant(left, declaredType) || isMatchingInFlowDiscriminant(left, type)) {
+                        if (isMatchingReferenceDiscriminant(right, declaredType) || isMatchingInFlowDiscriminant(right, type)) {
                             return narrowTypeByDiscriminant(type, <AccessExpression>right, t => narrowTypeByEquality(t, operator, left, assumeTrue));
                         }
                         if (containsMatchingReferenceDiscriminant(reference, left) || containsMatchingReferenceDiscriminant(reference, right)) {

Original file line number	Diff line number	Diff line change
`@@ -16269,7 +16269,7 @@ namespace ts {`
`16269`	`16269`	`if (isMatchingReferenceDiscriminant(left, declaredType) \|\| isMatchingInFlowDiscriminant(left, type)) {`
`16270`	`16270`	`return narrowTypeByDiscriminant(type, <AccessExpression>left, t => narrowTypeByEquality(t, operator, right, assumeTrue));`
`16271`	`16271`	`}`
`16272`		`- if (isMatchingReferenceDiscriminant(left, declaredType) \|\| isMatchingInFlowDiscriminant(left, type)) {`
	`16272`	`+ if (isMatchingReferenceDiscriminant(right, declaredType) \|\| isMatchingInFlowDiscriminant(right, type)) {`
`16273`	`16273`	`return narrowTypeByDiscriminant(type, <AccessExpression>right, t => narrowTypeByEquality(t, operator, left, assumeTrue));`
`16274`	`16274`	`}`
`16275`	`16275`	`if (containsMatchingReferenceDiscriminant(reference, left) \|\| containsMatchingReferenceDiscriminant(reference, right)) {`