Support rendering the content of a specific page to static HTML string #204

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Feature request

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What problem does this feature solve?

Currently saber-plugin-feed uses raw content in the generated feed:

https://github.com/saberland/saber/blob/7e32a24e45ea1559f97fee9c53a4ff702af13420/packages/saber-plugin-feed/lib/index.js#L70

This is fine if the page content has absolutely no Vue components, but unfortunately markdown links are compiled to <saber-link>, and we support many other Vue SFC features in pages.

So we should find a way to transform page.content to real/valid HTML.

What does the proposed API look like?

const html = await api.renderer.renderPartial({ url: 'the permalink' })

How should this be implemented in your opinion?

const context = {
  url: '...',
  // ...
  replaceRouteComponentWithThis: {
    return { 
      props: ['page'],
      render() { return h('div', {id:'__saber_content'}, this.$slots.default) }
    }
  }
}

const html = await renderer.renderToString(context)

// then somehow get the html of #__saber_content
// e.g. use posthtml

Are you willing to work on this yourself?