fix hasExhaustiveCaseClauses for 'case never:'

Author: ajafff

CHANGELOG.md

@@ -9,7 +9,7 @@
 **Bugfixes:**
 
 * `getConstructorTypeOfClassLikeDeclaration` now really returns the constructor type (the static side of the class), previously it returned the instance type
-* `hasExhaustiveCaseClauses` allows additional case clauses with `null` and `undefined`
+* `hasExhaustiveCaseClauses` allows additional case clauses with `null`, `undefined` and `never`
 
 # 3.18.0
 

test/rules/exhaustive-switch/test.ts.lint

@@ -65,6 +65,7 @@ declare function get<T>(): T;
         case 1:
         case null:
         case undefined:
+        case get<never>():
             return;
     }
     debugger;

util/util.ts

@@ -1710,7 +1710,10 @@ export function hasExhaustiveCaseClauses(node: ts.SwitchStatement, checker: ts.T
         return false;
     const seen = new Set<string | undefined>();
     for (const clause of caseClauses) {
-        const type = getPrimitiveLiteralFromType(checker.getTypeAtLocation(clause.expression));
+        const expressionType = checker.getTypeAtLocation(clause.expression);
+        if (isTypeFlagSet(expressionType, ts.TypeFlags.Never))
+            continue; // additional case clause with 'never' is always allowed
+        const type = getPrimitiveLiteralFromType(expressionType);
         if (types.has(type)) {
             seen.add(type);
         } else if (type !== 'null' && type !== 'undefined') { // additional case clauses with 'null' and 'undefined' are always allowed