Allow customization of generated files

[tobiasdiez]

Most presets are writing files that configure the deployment behavior (and are specific to the vendor used for the deployment). Sometimes, one needs to extend these configuration files and add/change certain things. For example, add custom (lambda) functions (https://github.com/nuxt/framework/discussions/2414, #266) or to add custom redirects by say modifying staticwebapp.config.json for Azure. Currently, the only option is to change the content of the generated files as a post-process step (e.g. in a custom preset), which involves loading, parsing and writing the content.

I think it would be more convenient and extensible if one could hook into the generation process and modify the corresponding js object before it is written to file. This could then look like:

// In the azure preset
....
config = callHook('staticwebapp.config.json', config)
await writeFile(resolve(nitro.options.rootDir, 'staticwebapp.config.json'), JSON.stringify(config))
....

// In the custom preset
export const azure = defineNitroPreset({
  extends: 'azure'
  hooks: {
    async 'staticwebapp.config.json' (config) {
      config.routes.push({
         route: 'my-custom-route',
         // configure, eg add redirection
      })
    }
  }
})