fix(eslint-plugin): [no-type-alias] consider keyof as an alias (typescript-eslint#3242)

Josh Goldberg · web-flow · commit 329ef023090c · 2021-03-29T12:38:30.000-07:00
diff --git a/packages/eslint-plugin/src/rules/no-type-alias.ts b/packages/eslint-plugin/src/rules/no-type-alias.ts
@@ -264,9 +264,10 @@ export default util.createRule<Options, MessageIds>({
         type.node.type.endsWith('Keyword') ||
         aliasTypes.has(type.node.type) ||
         (type.node.type === AST_NODE_TYPES.TSTypeOperator &&
-          type.node.operator === 'readonly' &&
-          type.node.typeAnnotation &&
-          aliasTypes.has(type.node.typeAnnotation.type))
+          (type.node.operator === 'keyof' ||
+            (type.node.operator === 'readonly' &&
+              type.node.typeAnnotation &&
+              aliasTypes.has(type.node.typeAnnotation.type))))
       ) {
         // alias / keyword
         checkAndReport(allowAliases!, isTopLevel, type, 'Aliases');
diff --git a/packages/eslint-plugin/tests/rules/no-type-alias.test.ts b/packages/eslint-plugin/tests/rules/no-type-alias.test.ts
@@ -394,6 +394,13 @@ export type ClassValue =
       code: 'type Foo = typeof bar;',
       options: [{ allowAliases: 'always' }],
     },
+    {
+      code: `
+const WithAKey = { AKey: true };
+type KeyNames = keyof typeof SCALARS;
+      `,
+      options: [{ allowAliases: 'always' }],
+    },
     {
       code: 'type Foo = typeof bar | typeof baz;',
       options: [{ allowAliases: 'in-unions' }],
