Environment API - Preview Environments

[jamesopstad]

The Environment API currently allows creating environments for dev and build but not for preview. Supporting environments when running vite preview would enable the build output to be previewed in the appropriate runtime (and in Cloudflare's case with the appropriate bindings etc.). This would also have the benefit of making it more straightforward to test build output.

Usage

• Preview environments can be created, similarly to dev and build environments.
• Plugins can access preview environments via the environments property on PreviewServer in the configurePreviewServer hook. This is equivalent to accessing dev environments in the configureServer hook.
• Plugins can add middleware that uses the PreviewEnvironment. This should have a similar interface to DevEnvironment (including dispatchFetch if that is agreed upon).

API

• Add preview option to EnvironmentOptions with PreviewEnvironmentOptions type:

interface PreviewEnvironmentOptions {
  createEnvironment?: (name: string, config: ResolvedConfig) =>
    Promise<PreviewEnvironment> | PreviewEnvironment
}

• Add PreviewEnvironment class:

class PreviewEnvironment extends BaseEnvironment {
  // implementation
}

• Add environments property to PreviewServer

Questions

• Are there other preview specific options that need to be added to PreviewEnvironmentOptions?
• Should build output locations simply be determined from the ResolvedConfig?