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sdk/eslint.config.js

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+import js from '@eslint/js'
+import globals from 'globals'
+import tseslint from 'typescript-eslint'
+
+/**
+ * ESLint configuration for the runtime SDK.
+ *
+ * The SDK is written in JavaScript with JSDoc types rather than TypeScript,
+ * because it is served as source to be read as well as to be executed. That
+ * choice drives the rule set:
+ *
+ *   - The rules designed for a `.ts` boundary (`explicit-module-boundary-types`)
+ *     are redundant here: a JSDoc `@returns` annotation is the same information,
+ *     and the linter cannot see it as an annotation.
+ *   - The rules that catch real defects — floating promises, misused promises,
+ *     unreachable switch cases, unused variables — stay, and are errors.
+ *   - `no-console` is an error rather than a warning, because this module runs in
+ *     someone else's page and must not write to their console on a path they did
+ *     not ask for. The two exceptions below are deliberate diagnostics that only
+ *     fire when the theme itself has already failed.
+ *
+ * The SDK is loaded by third-party pages, so anything it gets wrong is somebody
+ * else's incident. The strictness here is proportionate to that.
+ */
+export default tseslint.config(
+  { ignores: ['dist', 'node_modules', '*.config.js'] },
+  js.configs.recommended,
+  ...tseslint.configs.recommendedTypeChecked,
+  ...tseslint.configs.stylisticTypeChecked,
+  {
+    languageOptions: {
+      parserOptions: { projectService: true, tsconfigRootDir: import.meta.dirname },
+      globals: { ...globals.browser, ...globals.es2022 },
+    },
+    plugins: { '@typescript-eslint': tseslint.plugin },
+    rules: {
+      // JSDoc already declares every boundary type in a JavaScript project.
+      '@typescript-eslint/explicit-module-boundary-types': 'off',
+      // A fetch stub that returns a Response directly has nothing to await.
+      '@typescript-eslint/require-await': 'off',
+      // `||` is deliberate where an empty string should fall through, which is
+      // not what `??` does.
+      '@typescript-eslint/prefer-nullish-coalescing': 'off',
+
+      // --- correctness -----------------------------------------------------
+      '@typescript-eslint/no-floating-promises': 'error',
+      '@typescript-eslint/no-misused-promises': 'error',
+      '@typescript-eslint/await-thenable': 'error',
+      '@typescript-eslint/switch-exhaustiveness-check': 'error',
+      // Disabled in this package. The DOM type definitions describe a fully
+      // featured modern browser, but the runtime guards below exist for Safari
+      // below 14 (no `MediaQueryList.addEventListener`) and for embedded
+      // webviews with no `matchMedia` at all. Those guards are load-bearing for
+      // the consumers this package exists to serve, and the rule reports them as
+      // dead code.
+      '@typescript-eslint/no-unnecessary-condition': 'off',
+      '@typescript-eslint/no-unnecessary-type-assertion': 'error',
+      '@typescript-eslint/consistent-type-imports': [
+        'error',
+        { prefer: 'type-imports', fixStyle: 'inline-type-imports' },
+      ],
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        { argsIgnorePattern: '^_', varsIgnorePattern: '^_', caughtErrors: 'none' },
+      ],
+
+      // --- host safety -----------------------------------------------------
+      'no-console': ['error', { allow: ['warn', 'error'] }],
+      eqeqeq: ['error', 'always', { null: 'ignore' }],
+      'prefer-const': 'error',
+      'no-var': 'error',
+      'object-shorthand': 'error',
+      // An unsubscribe function that does nothing is the correct return value
+      // when there is nothing to unsubscribe from.
+      '@typescript-eslint/no-empty-function': [
+        'error',
+        { allow: ['arrowFunctions'] },
+      ],
+    },
+  },
+  {
+    // Tests build doubles that are deliberately loosely typed, and a test's
+    // console output is how a failure is diagnosed.
+    files: ['**/*.test.js'],
+    rules: {
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/no-unsafe-assignment': 'off',
+      '@typescript-eslint/no-unsafe-member-access': 'off',
+      '@typescript-eslint/no-unsafe-call': 'off',
+      '@typescript-eslint/no-unsafe-return': 'off',
+      '@typescript-eslint/unbound-method': 'off',
+      'no-console': 'off',
+    },
+  },
+)