Markdown extension is opening thousands of files

[OmarTawfik]

• VSCode Version: latest master

Problem

I've an extension/language server that lints files on file open. The linters are expensive and sometimes take a couple of seconds to run (an external process invocation). Multiple users reported that sometimes their linters would suddenly spike to hundreds/thousands of checks, without the user obviously opening these files.

Root Cause

I tracked it down to the built-in extension markdown-language-features. It performs a local file search on all markdown files in the workspace, ignoring node_modules, then opens each file.

For non Node.js projects, where they keep their build/out files in different folders, this is a huge performance issue. I'm not sure why does it need to open the file in the editor, instead of a file read, but if a user opens a workspace with hundreds/thousands of markdown files, the editor shouldn't try to open all of them!

With this extension activated, the vscode.workspace.onDidOpenTextDocument event is completely ubusable.

[mjbvz]

Duplicate of #50874