feat(front-import): change to type safe json parse

gui/frontend/src/lib/storage/cacheKeys.ts

@@ -1,3 +1,5 @@
+/// The reason for the key value pairs is to simplify refactoring of the language server.
+/// If we leave them as strings, we cannot automate symbol changes.
 import { OBJECT } from '@/lib/object-utils';
 
 const FORM_PUB_CACHE_KEYS_OBJ = {

gui/frontend/src/services/api/backup.ts

@@ -7,28 +7,38 @@ import { readFile, writeFile } from './fs';
 
 const SETTINGS_FILE_NAME = 'settings';
 
+/** ref: [better-typescript-lib article(ja)](https://zenn.dev/uhyo/articles/better-typescript-lib-v2#better-typescript-lib-%E3%81%AB%E3%81%A4%E3%81%84%E3%81%A6) */
+function isPropertyAccessible(obj: unknown): obj is Record<string, unknown> {
+  return obj !== null;
+}
+
 export const BACKUP = {
   /** @throws Error */
-  async import() {
+  async import(): Promise<Cache | null> {
     const settings = await readFile(PRIVATE_CACHE_OBJ.importSettingsPath, SETTINGS_FILE_NAME);
-    if (settings) {
-      const obj = JSON.parse(settings);
-
-      // Validate
-      for (const key of Object.keys(obj)) {
-        if (key === PRIVATE_CACHE_OBJ.importSettingsPath) {
-          continue; // The import path does not need to be overwritten.
-        }
-
-        // Remove invalid settings values
-        const isInvalidKey = !CACHE_KEYS.some((cacheKey) => cacheKey === key);
-        if (isInvalidKey) {
-          delete obj[key];
-        }
+    if (settings === null) {
+      return null;
+    }
+
+    const json = JSON.parse(settings);
+    if (!isPropertyAccessible(json)) {
+      return null;
+    }
+
+    // Validate
+    for (const key of Object.keys(json)) {
+      if (key === PRIVATE_CACHE_OBJ.importSettingsPath) {
+        continue; // The import path does not need to be overwritten.
       }
 
-      return obj as Cache;
+      // Remove invalid settings values
+      const isInvalidKey = !CACHE_KEYS.some((cacheKey) => cacheKey === key);
+      if (isInvalidKey) {
+        delete json[key];
+      }
     }
+
+    return json;
   },
 
   /** @throws Json parse Error */