chore: upgrade eslint to v9

eslint.config.js

@@ -0,0 +1,54 @@
+import js from '@eslint/js';
+import ts from 'typescript-eslint';
+import svelte from 'eslint-plugin-svelte';
+import prettier from 'eslint-config-prettier';
+import globals from 'globals';
+
+/** @type {import('eslint').Linter.Config[]} */
+export default [
+	js.configs.recommended,
+	...ts.configs.recommended,
+	...svelte.configs['flat/recommended'],
+	prettier,
+	{
+		languageOptions: {
+			globals: {
+				...globals.browser,
+				...globals.node,
+			},
+		},
+	},
+	{
+		files: ['**/*.svelte'],
+		languageOptions: {
+			parserOptions: {
+				parser: ts.parser,
+				svelteFeatures: {
+					experimentalGenerics: true,
+				},
+			},
+		},
+	},
+	{
+		ignores: [
+			'**/.svelte-kit',
+			'**/build',
+			'**/node_modules',
+			'**/static',
+			'**/package',
+			'**/lz-string/*',
+		],
+	},
+	{
+		rules: {
+			'@typescript-eslint/no-unused-vars': [
+				'error',
+				{
+					argsIgnorePattern: '^(_|\\$\\$)',
+					varsIgnorePattern: '^(_|\\$\\$)',
+					caughtErrorsIgnorePattern: '^(_|\\$\\$)',
+				},
+			],
+		},
+	},
+];

package.json

@@ -46,10 +46,10 @@
 		"@sveltejs/kit": "^2.5.0",
 		"@sveltejs/package": "^2.2.6",
 		"@svitejs/changesets-changelog-github-compact": "^1.1.0",
-		"@typescript-eslint/eslint-plugin": "^7.0.2",
-		"@typescript-eslint/parser": "^7.0.2",
-		"eslint": "^8.56.0",
-		"eslint-plugin-svelte": "^2.35.1",
+		"eslint": "^9.8.0",
+		"eslint-config-prettier": "^9.1.0",
+		"eslint-plugin-svelte": "^2.43.0",
+		"globals": "^15.8.0",
 		"prettier": "^3.2.5",
 		"prettier-plugin-svelte": "^3.2.1",
 		"svelte": "^4.2.11",
@@ -58,6 +58,7 @@
 		"svelte-typewriter-store": "^0.0.5",
 		"tslib": "^2.6.2",
 		"typescript": "^5.0.0",
+		"typescript-eslint": "8.0.0-alpha.54",
 		"vite": "^5.1.3",
 		"vitest": "^2.0.0"
 	},

playground/src/routes/+page.svelte

@@ -16,15 +16,18 @@
 	let lz_changes = 0;
 
 	$: {
+		// eslint-disable-next-line @typescript-eslint/no-unused-expressions
 		$obj;
 		obj_changes++;
 	}
 
 	$: {
+		// eslint-disable-next-line @typescript-eslint/no-unused-expressions
 		$arr;
 		arr_changes++;
 	}
 	$: {
+		// eslint-disable-next-line @typescript-eslint/no-unused-expressions
 		$lz;
 		lz_changes++;
 	}

playground/src/routes/equalityFn/+page.svelte

@@ -8,6 +8,7 @@
 
 	let obj_changes = 0;
 	$: {
+		// eslint-disable-next-line @typescript-eslint/no-unused-expressions
 		$obj;
 		obj_changes++;
 	}
@@ -25,6 +26,7 @@
 
 	let store_changes = 0;
 	$: {
+		// eslint-disable-next-line @typescript-eslint/no-unused-expressions
 		$params;
 		store_changes++;
 	}

playground/src/routes/queryparameters/+page.svelte

@@ -22,6 +22,7 @@
 	let change_in_store = 0;
 
 	$: {
+		// eslint-disable-next-line @typescript-eslint/no-unused-expressions
 		$store;
 		change_in_store++;
 	}