Feature Request: Option to exclude barrel files from `output.banner`

[alario-tang]

Feature Request: Option to exclude barrel files from output.banner

Problem

When using pluginClient with output.banner: "'use server'" for Next.js Server Actions, all generated files receive this directive, including:

1. Barrel files (index.ts) - only do re-exports
2. Group aggregation files (stocks/stocks.ts, broker/broker.ts, etc.) - generated when using group option

These files should NOT have "use server" because:

• Barrel files only re-export, they don't define server actions
• Aggregation files return function references which cannot be serialized in server actions

Current Workaround

We have to use hooks.done with a post-processing script to remove "use server" from barrel files:

// kubb.config.ts
export default defineConfig({
  hooks: {
    done: ['bash scripts/remove-use-server-from-barrels.sh'],
  },
  plugins: [
    pluginClient({
      output: {
        path: './api',
        banner: "'use server'",
        barrelType: 'named',
      },
      group: { type: 'tag', name: ({ group }) => camelCase(group) },
    }),
  ],
});

# remove-use-server-from-barrels.sh
# Remove "use server" from dir/dir.ts pattern files
find src/actions-generated/api -regex '.*/\([^/]*\)/\1\.ts' -exec perl -i -pe 's/"use server";//' {} \;

Proposed Solution

Add an option to exclude barrel/aggregation files from banner injection:

Option A: bannerExcludeBarrel

pluginClient({
  output: {
    path: './api',
    banner: "'use server'",
    bannerExcludeBarrel: true,  // Don't add banner to index.ts and dir/dir.ts files
  },
}),

Option B: banner as function with file context

pluginClient({
  output: {
    path: './api',
    banner: ({ isBarrel, isAggregation, filePath }) => {
      if (isBarrel || isAggregation) return '';
      return "'use server'";
    },
  },
}),

Option C: Separate barrelBanner option

pluginClient({
  output: {
    path: './api',
    banner: "'use server'",
    barrelBanner: '',  // Override banner for barrel files
  },
}),

Environment

• Kubb version: 4.12.15
• Framework: Next.js 16.1 (App Router with Server Actions)
• Plugins: @kubb/plugin-client, @kubb/plugin-ts, @kubb/plugin-zod

Additional Context

This is a common use case for Next.js users who want to:

1. Generate type-safe API clients with Kubb
2. Use them as Server Actions (requires "use server" directive)
3. Organize code with group option for better structure

The current workaround requires platform-specific scripts (bash/perl) which is not ideal for cross-platform development.

[stijnvanhulle]

Maybe Barrel files do not have banners at all? We simply dont add banners en footers to 'index.ts' files?
@alario-tang

[alario-tang]

@stijnvanhulle sorry, I mean [dir]/[dir.ts], like stocks/stocks.ts, broker/broker.ts
maybe like this: (pseudocode)

banner:
if (isGroupAggregation) return "";
else return "use server";