Add assertion.

DanielRosenwasser · DanielRosenwasser · commit 40c3ffec91bd · 2020-06-30T01:33:32.000-07:00
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -16130,6 +16130,7 @@ namespace ts {
 
                 if (isLiteralType(source) && !typeCouldHaveTopLevelSingletonTypes(target)) {
                     generalizedSource = getBaseTypeOfLiteralType(source);
+                    Debug.assert(!isTypeAssignableTo(generalizedSource, target), "generalized source shouldn't be assignable");
                     generalizedSourceType = getTypeNameForErrorDisplay(generalizedSource);
                 }
 

Original file line number	Diff line number	Diff line change
`@@ -16130,6 +16130,7 @@ namespace ts {`
`16130`	`16130`
`16131`	`16131`	`if (isLiteralType(source) && !typeCouldHaveTopLevelSingletonTypes(target)) {`
`16132`	`16132`	`generalizedSource = getBaseTypeOfLiteralType(source);`
	`16133`	`+ Debug.assert(!isTypeAssignableTo(generalizedSource, target), "generalized source shouldn't be assignable");`
`16133`	`16134`	`generalizedSourceType = getTypeNameForErrorDisplay(generalizedSource);`
`16134`	`16135`	`}`
`16135`	`16136`