Support absolute paths for `layout` and `partials` properties for Handlebars

[ludovicm67]

Prerequisites

• [X] I have written a descriptive issue title
• [X] I have searched existing issues to ensure the feature has not already been requested

🚀 Feature Proposal

Allow the use of absolute paths to configure the root, the layout and the options.partials properties when Handlebars is used.

Motivation

The files on the file system are like this:

views/
  layouts/
    main.hbs
  home.hbs

Right now, when I try to use absolute paths for layout, the app crashes with the following error:

Error: unable to access template "/absolute/path/to/views/layouts/main.hbs"

If I cat that exact same path, I'm able to see my template file. So there is an issue.

I have a use-case where I need to allow a user to configure the full path of the layout, the path of the templates and the paths to some partials and the views independently.

Example

This is a basic example of code that is currently not supported:

import { dirname, join } from 'path'
import { fileURLToPath } from 'url'
import fastify from 'fastify'
import fastifyView from '@fastify/view'
import Handlebars from 'handlebars'

const currentDir = dirname(fileURLToPath(import.meta.url))

const server = fastify({
  logger: true,
})

server.register(fastifyView, {
  engine: {
    handlebars: Handlebars
  },
  root: join(currentDir, 'views'),
  viewExt: 'hbs',
  includeViewExtension: true,
  layout: join(currentDir, 'views', 'layouts', 'main.hbs'),
  defaultContext: {
    title: 'My App'
  },
})

Maybe I'm doing something wrong? I'm also open to any suggestion to get this working.