Updates

.vscode/settings.json

@@ -15,5 +15,18 @@
   },
   "rewrap.wrappingColumn": 100,
   "rust-analyzer.cargo.features": "all",
-  "typescript.tsdk": "frontend/node_modules/typescript/lib"
+  "typescript.tsdk": "frontend/node_modules/typescript/lib",
+  "eslint.options": {
+    "flags": ["unstable_ts_config"]
+  },
+  "eslint.workingDirectories": [
+    "frontend"
+  ],
+  "eslint.useFlatConfig": true,
+  "eslint.validate": [
+    "javascript",
+    "typescript",
+    "svelte"
+  ],
+  "svelte.enable-ts-plugin": true
 }

frontend/eslint.config.ts

@@ -0,0 +1,110 @@
+import js from '@eslint/js';
+import ts from 'typescript-eslint';
+import {type TSESLint} from '@typescript-eslint/utils';
+import svelte from 'eslint-plugin-svelte';
+import svelteParser from 'svelte-eslint-parser';
+import globals from 'globals';
+
+/** Files that should be ignored globally by eslint. */
+const IGNORES = [
+    // Temporary files, generated files, dependencies
+    '**/.DS_Store',
+    '**/node_modules',
+    'build',
+    '.svelte-kit',
+    'package',
+    '**/.env',
+    '**/.env.*',
+    '!**/.env.example',
+    '**/package-lock.json',
+
+    // Certain third party libs
+    'static/js/elements.flagmeister.min.js',
+    'static/js/maplibre-gl.js',
+    'static/js/*.component.js',
+];
+
+/** Files that should be ignored globally by typescript-eslint. */
+const IGNORES_TS = ['**/*.js', '**/*.mjs', '**/*.cjs'];
+
+/**
+ * Apply the {@link IGNORES_TS} ignore to the specified config array.
+ */
+function typescriptOnly(
+    configArray: TSESLint.FlatConfig.ConfigArray,
+): TSESLint.FlatConfig.ConfigArray {
+    return configArray.map((config) => ({
+        ...config,
+        ignores: IGNORES_TS,
+    }));
+}
+
+export default ts.config(
+    // Ignore certain files
+    {ignores: IGNORES},
+
+    // Apply JS base config
+    js.configs.recommended,
+
+    // Apply TS base config (but not to plain-JS files)
+    ...typescriptOnly(ts.configs.recommendedTypeChecked),
+    //...ts.configs.strictTypeChecked, // TODO
+    //...ts.configs.stylisticTypeChecked, // TODO
+
+    // Apply Svelte config
+    ...svelte.configs['flat/prettier'],
+
+    // Configure language options
+    {
+        languageOptions: {
+            ecmaVersion: 2023,
+            globals: {
+                ...globals.browser,
+                ...globals.node,
+            },
+            parserOptions: {
+                projectService: true,
+                extraFileExtensions: ['.svelte'],
+            },
+        },
+    },
+    {
+        files: ['**/*.svelte'],
+        languageOptions: {
+            parser: svelteParser,
+            ecmaVersion: 2023,
+            sourceType: 'script',
+            parserOptions: {
+                parser: '@typescript-eslint/parser',
+            },
+        },
+    },
+
+    // Configure general rules
+    {
+        rules: {
+            // Creates a lot of false positives, e.g. when throwing redirect()
+            '@typescript-eslint/only-throw-error': 'off',
+            // Disallows putting unknown caught errors in messages
+            '@typescript-eslint/restrict-template-expressions': 'off',
+        },
+    },
+
+    // Configure test rules
+    {
+        rules: {
+            '@typescript-eslint/no-unused-expressions': 'off',
+        },
+        files: ['**/*.test.ts'],
+    },
+
+    // Configure SvelteKit rules
+    {
+        rules: {
+            // Lots of false positives, see https://github.com/sveltejs/eslint-plugin-svelte/issues/413
+            '@typescript-eslint/no-unsafe-call': 'off',
+            '@typescript-eslint/no-unsafe-member-access': 'off',
+        },
+        files: ['**/+page.svelte'],
+    },
+);