Folder icon for folder containing definitions only

I am not sure if it is possible to change icon based of folder content, but if not, simple definition(s?) detection would do it.

I would see it beeping similar to the .d.ts files, black with blue border and TS written on it?

[PKief]

You can also define your custom folder associations in your User Settings like this:

"material-icon-theme.folders.associations": {
    "definition": "typescript",
    "definitions": "typescript"
}

After a restart of the editor the icon will look like this:

[PKief]

As far as it is currently not possible to adjust folder icons by the containing files this issue seems to be solved by using the custom folder associations. So I’m going to close the issue for now. When the API of VS Code will be updated regarding this feature, I’ll come back to this issue. Thank you for your request.