Allow re-rendering Markdown preview when updated extra configurations provided by extension

[yhatt]

If Markdown extension provides some extra settings to affect the rendering of Markdown, it would want to re-render Markdown preview when changed configuration values. In fact, VS Code built-in configurations (e.g. markdown.preview.breaks) will behave like that. (Tested in 1.33.0-insider)

I have met with such a case while creating a Markdown extension that has configurable rendering, but I could not find a way to re-trigger Markdown rendering manually. markdown.preview.refresh command is meaningless because it just refresh WebView and not triggered a rendering process.

import { ExtensionContext, commands, workspace } from 'vscode'

export const activate = ({ subscriptions }: ExtensionContext) => {
  subscriptions.push(
    workspace.onDidChangeConfiguration(e => {
      if (e.affectsConfiguration('extension.configuration')) {
        // FIXME: `markdown.preview.refresh` won't re-trigger rendering
        commands.executeCommand('markdown.preview.refresh')
      }
    })
  )

  return {
    extendMarkdownIt: md => {
      md.use(() => {
        const conf = workspace.getConfiguration('extension').get('configuration')
        // ... and use configured value in markdown-it plugin ...
      })
    }
  }
}

Thus, user have to change Markdown buffer once for previewing with updated configurations. Probably many users would expect to reflect the changed configuration to preview immediately.

It would be awesome if there was a command (or API for extension) to re-trigger rendering of Markdown.

[mjbvz]

PRs welcome to make the refresh command re-render

[vitaliymaz]

Reproducible for me, can I work on the PR?

[vitaliymaz]

The problem happens with cached tokens here
https://github.com/Microsoft/vscode/blob/2f2085f3e1e3c75916ea950d5c8c2e1e4c28b3dd/extensions/markdown-language-features/src/markdownEngine.ts#L121

It makes a decision whether to recalculate tokens based on the document version and markdown extension configurations. But it doesn't consider changing configurations of markdownItPlugins.

There are two possible solutions I see:

1. Extract configurations of all plugins which extend markdown base plugin and recalculate tokens if something changed there.
2. Clean tokens cache on refresh command or pass some force flag.

@mjbvz , maybe you can help me with a decision.

[yhatt]

IMO I prefer 2, a controllable way in per extension.

Some settings defined in Markdown extension would not require clearing cache. I'm afraid to degraded performance.

In addition, I have an extension that must trigger re-rendering Markdown by VSCode native configuration window.zoomLevel. It does not defined in the extension. (marp-team/marp-vscode#8 (comment))

[mjbvz]

@vitaliymaz I'm in favor of the second approach as well: making the refresh command flush the cache. That way it's entirely up to the extension to say when the preview is refreshed

[vitaliymaz]

@mjbvz, thank you for the feedback. Working on the second approach.

[mjbvz]

Fixed by #71442

[yhatt]

Thanks @mjbvz, and @vitaliymaz's awesome work! I'll start to test in the next insider version. Cheers 🍻

UPDATE: 1.34 is getting work 😄