extract markdown into an extension

[kieferrm]

Extracts colorizing and previewing of markdown files into its own extension as described in #6106.

[mention-bot]

By analyzing the blame information on this pull request, we identified @egamma and @jrieken to be potential reviewers

[jrieken]

do we need monaco-editor?
and for the sake of being aligned and explicit should we call the theme classes: vscode-light, vscode-dark, and vscode-high-contrast?

[jrieken]

@kieferrm We have some hygiene failure due to missing copy right statements

[cbreeden]

If you don't mind me asking. As it is coded here, anytime a member wants to add a plugin to markdown-it, it seems they will have to:

1. Npm install markdown-it-plugin --savedev in extensions folder
2. Require package here and add package to .use(...)

This seems fine to me, but I believe that also means I would have to do this every time that extension is updated. I don't know of a good solution, but one solution I thought of is to allow for developers to create a "skeleton" package that simply exposes and api to the markdown extension that says use this. So people will be able to install a package, say: vscode-markdown-it-katex for math support which has a dependency on this package and it should just work. Not an ideal solution, but maybe there is a better one? I could open this as a feature request if you would like to defer this until another cycle. Or possibly a pull request later on.

[rebornix]

@cbreeden your request is valid to me. People always need to customize the Markdown rendering process to meet their need. A final perfect solution is allowing users to load markdown-it anomynous extensions on the fly. But I don't find this feature documented on their website. So personaly I suggest:

1. Find out or add on-the-fly loading mechanism for markdown-it. Maybe create a feature request on their repo.
2. Emebed this feature into our seperate Markdown Extension. Provide users a configuration (an array is simple enough) to inject their markdown-it extensions written in JS.

Since we've already moved the markdown stuff out of VS Code, we may want to keep all related features in markdown or its dependencies instead of here.

If you are willing to help file these issues/requests to corresponding repositories, it would be really awesome. Otherwise I can do it myself.

[cbreeden]

Sounds great. Could you help me try to understand a little better how to implement this? I believe that .use is on the 'on-the-fly' as in it should work something like this:

var md = require('markdown-it')();
var mathPlugin = require('markdown-it-katex');

md.render('$1 \\over 2$'); // renders '$1 \\over 2$' in paragraph tag

md = md.use(mathPlugin);
md.render('$1 \\over 2$'); // renders '1/2' in new fancy math

So you could certainly iterate over a list of plugins to attach them. The issue is that I am not exactly sure how I would get the extension to obtain the mathPlugin object from a settings list. Also how to make this list persist through extension updates. Do you have any ideas?

Minor note: There are some other methods for extending markdown-it where you override the rendering functions to meet special needs. It's very similar to what vscode already has. But just getting the plugins to load would be great and worry about this later maybe.

[rebornix]

When I say on-the-fly, it's more or less loading anomynous plugins:

plugins.each((ext) => {
  md.use(ext);
})

This is what we need to figure out (I have no idea about this either for now).

Updating is another topic. One solution is keeping our hands clean by only allowing users to inject javascript files and let users update the plugins themselves. Otherwise we need careful design about plugin upgrade.

[jrieken]

For markdown-it plugins I suggest that we explore a path via settings. For instance, a user can manually configure additional plugins to use in settings.json like markdown.plugins: ["p1", "p2"]. We would try to find and configure them, but not install them.

[jrieken]

@aeschli There is an integration test failure (https://travis-ci.org/Microsoft/vscode/jobs/137741881#L2247) with those changes. I believe this is cos we have added new token types etc and I guess you know for sure and how to fix it.