perf(linter/plugins): small perf optimizations (#14420)

Follow-on after #14415 and #14416. Perf micro-optimizations.

Author: overlookmotel

apps/oxlint/src-js/plugins/context.ts

@@ -6,7 +6,7 @@ import type { Fix, FixFn } from './fix.ts';
 import type { SourceCode } from './source_code.ts';
 import type { Location, Ranged } from './types.ts';
 
-const { hasOwn } = Object;
+const { hasOwn, keys: ObjectKeys } = Object;
 
 // Diagnostic in form passed by user to `Context#report()`
 export type Diagnostic = DiagnosticWithNode | DiagnosticWithLoc | DiagnosticWithMessageId;
@@ -161,8 +161,7 @@ export class Context {
     // Resolve message from messageId if present
     let message: string;
     if (hasOwn(diagnostic, 'messageId')) {
-      const diagWithMessageId = diagnostic as DiagnosticWithMessageId;
-      message = resolveMessage(diagWithMessageId.messageId, internal);
+      message = resolveMessage((diagnostic as DiagnosticWithMessageId).messageId, internal);
     } else {
       message = diagnostic.message;
       if (typeof message !== 'string') {
@@ -249,15 +248,14 @@ export class Context {
  */
 function resolveMessage(messageId: string, internal: InternalContext): string {
   const { messages } = internal;
-
-  if (!messages) {
+  if (messages === null) {
     throw new Error(`Cannot use messageId '${messageId}' - rule does not define any messages in meta.messages`);
   }
 
   if (!hasOwn(messages, messageId)) {
     throw new Error(
       `Unknown messageId '${messageId}'. Available messages: ${
-        Object.keys(messages).map((msg) => `'${msg}'`).join(', ')
+        ObjectKeys(messages).map((msg) => `'${msg}'`).join(', ')
       }`,
     );
   }

apps/oxlint/src-js/plugins/load.ts

@@ -134,11 +134,10 @@ async function loadPluginImpl(path: string): Promise<PluginDetails> {
       }
 
       // Extract messages for messageId support
-      if (ruleMeta.messages != null) {
-        if (typeof ruleMeta.messages !== 'object' || Array.isArray(ruleMeta.messages)) {
-          throw new TypeError('Invalid `meta.messages` - must be an object');
-        }
-        messages = ruleMeta.messages;
+      const inputMessages = ruleMeta.messages;
+      if (inputMessages != null) {
+        if (typeof inputMessages !== 'object') throw new TypeError('`meta.messages` must be an object if provided');
+        messages = inputMessages;
       }
     }