Migrate eslint to v9

.eslintrc

@@ -33,6 +33,6 @@
     "@typescript-eslint/no-non-null-assertion": "off",
     "@typescript-eslint/explicit-module-boundary-types": "off",
     "@typescript-eslint/semi": ["warn"],
-    "@typescript-eslint/member-delimiter-style": ["warn"]
+    "@typescript-eslint/member-delimiter-style": "warn"
   }
 }

eslint.config.mjs

@@ -0,0 +1,63 @@
+import tsParser from "@typescript-eslint/parser";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import js from "@eslint/js";
+import { FlatCompat } from "@eslint/eslintrc";
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const compat = new FlatCompat({
+    baseDirectory: __dirname,
+    recommendedConfig: js.configs.recommended,
+    allConfig: js.configs.all
+});
+
+export default [{
+    ignores: ["**/dist"],
+}, ...compat.extends(
+    "eslint:recommended",
+    "plugin:@typescript-eslint/eslint-recommended",
+    "plugin:@typescript-eslint/recommended",
+), {
+    languageOptions: {
+        parser: tsParser,
+        ecmaVersion: 2018,
+        sourceType: "module",
+    },
+
+    rules: {
+        quotes: ["warn", "single"],
+
+        indent: ["warn", 2, {
+            SwitchCase: 1,
+        }],
+
+        semi: ["off"],
+        "comma-dangle": ["warn", "always-multiline"],
+        "dot-notation": "off",
+        eqeqeq: "warn",
+        curly: ["warn", "all"],
+        "brace-style": ["warn"],
+        "prefer-arrow-callback": ["warn"],
+        "max-len": ["warn", 140],
+        "no-console": ["warn"],
+        "no-non-null-assertion": ["off"],
+        "comma-spacing": ["error"],
+
+        "no-multi-spaces": ["warn", {
+            ignoreEOLComments: true,
+        }],
+
+        "no-trailing-spaces": ["warn"],
+
+        "lines-between-class-members": ["warn", "always", {
+            exceptAfterSingleLine: true,
+        }],
+
+        "@typescript-eslint/explicit-function-return-type": "off",
+        "@typescript-eslint/no-non-null-assertion": "off",
+        "@typescript-eslint/explicit-module-boundary-types": "off",
+        "@typescript-eslint/semi": ["warn"],
+        "@typescript-eslint/member-delimiter-style": "warn",
+    },
+}];