Summary

Refine the Bundler interface and bundler configuration hooks to give plugin authors the tools they need to configure bundler-specific behavior correctly and completely.

Problems & Rationale

1. Complex comparison to identify the active bundler

Plugins in extendsBundlerOptions need to know which bundler is active to add the right options (e.g. viteOptions vs chainWebpack). The only discriminator was bundler.name, which is the full scoped package name.

- app.options.bundler.name === '@vuepress/bundler-webpack'
+ app.options.bundler.type === 'webpack'

2. Missing merge helper in extendsBundlerOptions

When a plugin accepts user bundler options and wants to merge them into the resolved options, it needs the correct merge function (vite.mergeConfig vs webpack-merge differ in semantics). The hook only passes (options, app) — no merge helper.

We considered adding mergeConfig as a hook parameter, but all extends* hooks share the uniform signature (extendable: T, app: App):

// hooks.ts — every extends hook follows this pattern
extendsMarkdownOptions: ExtendsHook<MarkdownOptions>
extendsMarkdown: ExtendsHook<Markdown>
extendsPageOptions: ExtendsHook<PageOptions>
extendsPage: ExtendsHook<Page>
extendsBundlerOptions: ExtendsHook<BundlerOptions>

Adding a third parameter would break this consistency. So mergeConfig is exposed on the Bundler object instead:

  export interface Bundler {
    name: string
+   type: string
    dev: (app: App) => Promise<() => Promise<void>>
    build: (app: App) => Promise<void>
+   mergeConfig: <Config extends Record<string, any>>(
+     currentConfig: Config,
+     newConfig: DeepPartial<Config>,
+   ) => Config
  }

Plugins access it naturally: app.options.bundler.mergeConfig(...).

3. configureWebpack / configureVite cannot remove array items

The old merge-on-return model was purely additive — array items could only be appended, never deleted.

  // resolveWebpackConfig.ts
  const configureWebpackResult = options.configureWebpack?.(...)

- // if `configureWebpack` returns a configuration object,
- // use webpack-merge to merge it
  if (configureWebpackResult) {
-   return merge(webpackConfig, configureWebpackResult)
+   webpackConfig = configureWebpackResult
  }

Returning a value now fully replaces the config. To merge explicitly, use the mergeConfig callback parameter passed to the hook.

Note: the mergeConfig from vite always create a fresh new object at every level while merging.

Breaking changes

• Bundler interface now requires type and mergeConfig.
• configureWebpack return value replaces the config. Use the passed mergeConfig parameter to merge instead.