Disable default-case ESLint rule for type-checked TypeScript files

eslint.cli.config.mjs

@@ -10,6 +10,9 @@ export default defineConfig([
     // This override adds type-checked rules.
     // Linting with type-checked rules is very slow and needs a lot of memory,
     // so we exclude non-essential files.
+    // NOTE: eslint.config.mjs has a config block that mirrors these
+    // `files`/`ignores` to override non-type-checked rules for the same set of
+    // files. Keep both in sync if you change the globs.
     ignores: [
       'bench/**/*',
       'examples/**/*',
@@ -27,7 +30,10 @@ export default defineConfig([
     rules: {
       // TODO: enable in follow-up PR
       '@typescript-eslint/no-floating-promises': 'off',
-      '@typescript-eslint/switch-exhaustiveness-check': 'error',
+      '@typescript-eslint/switch-exhaustiveness-check': [
+        'error',
+        { requireDefaultForNonUnion: true },
+      ],
     },
   },
 ])

eslint.config.mjs

@@ -394,6 +394,30 @@ export default defineConfig([
       '@typescript-eslint/prefer-literal-enum-member': 'error',
     },
   },
+  {
+    // This block mirrors the `files`/`ignores` of the type-checked config in
+    // eslint.cli.config.mjs, so it targets exactly the files for which those
+    // type-aware rules run. Use it to override non-type-checked rules whose
+    // behavior overlaps with a type-checked rule. Keep the globs below in sync
+    // with eslint.cli.config.mjs.
+    files: ['**/*.ts', '**/*.tsx'],
+    ignores: [
+      'bench/**/*',
+      'examples/**/*',
+      'test/**/*',
+      '**/*.d.ts',
+      'turbopack/**/*',
+    ],
+    rules: {
+      // `@typescript-eslint/switch-exhaustiveness-check` already enforces
+      // complete switch coverage on these files: every member of a union or
+      // enum must be handled, and with `requireDefaultForNonUnion` a default
+      // is required for switches on plain types (string, number, …). Leaving
+      // `default-case` on would additionally force a redundant default on
+      // exhaustive union/enum switches.
+      'default-case': 'off',
+    },
+  },
   {
     files: ['packages/**/*.ts', 'packages/**/*.tsx'],
     plugins: {

packages/next/src/build/webpack/loaders/postcss-loader/src/index.ts

@@ -83,7 +83,6 @@ export default async function loader(
       }
 
       for (const message of result.messages) {
-        // eslint-disable-next-line default-case
         switch (message.type) {
           case 'dependency':
             this.addDependency(message.file)
@@ -109,6 +108,9 @@ export default async function loader(
                 message.info
               )
             }
+            break
+          default:
+            break
         }
       }
 

packages/next/src/shared/lib/head.tsx

@@ -73,7 +73,6 @@ function unique() {
       }
     }
 
-    // eslint-disable-next-line default-case
     switch (h.type) {
       case 'title':
       case 'base':
@@ -106,6 +105,8 @@ function unique() {
           }
         }
         break
+      default:
+        break
     }
 
     return isUnique