feat!: upgrade eslint to v9

This adds new rules and requires an dependency update so is a breaking change

Author: OliverDudgeon

eslint.config.js

@@ -1,13 +1,13 @@
 import js from "@eslint/js";
-import eslintImport, { rules } from "eslint-plugin-import-x";
+import nextPlugin from "@next/eslint-plugin-next";
+import eslintImport from "eslint-plugin-import-x";
 import * as mdx from "eslint-plugin-mdx";
 import react from "eslint-plugin-react";
 import reactHooks from "eslint-plugin-react-hooks";
 import simpleImportSort from "eslint-plugin-simple-import-sort";
 import eslintPluginUnicorn from "eslint-plugin-unicorn";
 import unusedImports from "eslint-plugin-unused-imports";
 import tseslint from "typescript-eslint";
-import nextPlugin from "@next/eslint-plugin-next";
 
 const tsParserOptions = {
   parser: tseslint.parser,
@@ -65,6 +65,7 @@ const standardRules = {
   "object-shorthand": ["warn"],
   "no-with": ["error"],
   "no-var": ["warn"],
+  "no-useless-assignment": "warn",
   "no-useless-return": ["warn"],
   "no-useless-rename": ["warn"],
   "no-useless-escape": ["warn"],
@@ -232,16 +233,16 @@ const simpleImportSortRules = {
         ],
         // React comes first
         ["^react"],
-        ["^\\u0000"],
+        [String.raw`^\u0000`],
         // Internal packages.
         ["^(@squonk)(/.*|$)"],
-        ["^@?\\w"],
+        [String.raw`^@?\w`],
         // Side effect imports.
         // Parent imports. Put `..` last.
         // Other relative imports. Put same-folder imports and `.` last.
-        ["^\\.\\.(?!/?$)", "^\\.\\./?$", "^\\./(?=.*/)(?!/?$)", "^\\.(?!/?$)", "^\\./?$"],
+        [String.raw`^\.\.(?!/?$)`, String.raw`^\.\./?$`, String.raw`^\./(?=.*/)(?!/?$)`, String.raw`^\.(?!/?$)`, String.raw`^\./?$`],
         // Style imports.
-        ["^.+\\.s?css$"],
+        [String.raw`^.+\.s?css$`],
       ],
     },
   ],

package.json

@@ -15,27 +15,22 @@
     "url": "https://github.com/InformaticsMatters/eslint-config-squonk/issues"
   },
   "homepage": "https://github.com/InformaticsMatters/eslint-config-squonk#readme",
-  "scripts": {
-  },
-  "peerDependencies": {
-    "eslint": "8",
-    "typescript": ">=4.7"
-  },
   "dependencies": {
-    "@eslint/js": "8.57.1",
-    "@next/eslint-plugin-next": "15.2.4",
-    "@types/node": "22.13.14",
-    "eslint": "8.57.1",
-    "eslint-import-resolver-typescript": "4.3.1",
-    "eslint-mdx": "3.3.1",
-    "eslint-plugin-import-x": "4.9.4",
-    "eslint-plugin-mdx": "3.3.1",
-    "eslint-plugin-react": "7.37.4",
+    "@eslint/eslintrc": "^3.3.1",
+    "@eslint/js": "9.25.1",
+    "@next/eslint-plugin-next": "15.3.1",
+    "@types/node": "22.14.1",
+    "eslint": "9.25.1",
+    "eslint-import-resolver-typescript": "4.3.4",
+    "eslint-mdx": "3.4.1",
+    "eslint-plugin-import-x": "4.10.6",
+    "eslint-plugin-mdx": "3.4.1",
+    "eslint-plugin-react": "7.37.5",
     "eslint-plugin-react-hooks": "5.2.0",
     "eslint-plugin-simple-import-sort": "12.1.1",
-    "eslint-plugin-unicorn": "52.0.0",
-    "eslint-plugin-unused-imports": "3.2.0",
-    "typescript": "5.8.2",
-    "typescript-eslint": "8.28.0"
+    "eslint-plugin-unicorn": "58.0.0",
+    "eslint-plugin-unused-imports": "4.1.4",
+    "typescript": "5.8.3",
+    "typescript-eslint": "8.31.0"
   }
 }