TextMate scope selectors: scope exclusion is not implemented

From @monk-time on September 4, 2017 14:51

• VSCode Version: Code 1.15.1 (41abd21afdf7424c89319ee7cb0445cc6f376959, 2017-08-16T18:07:25.676Z)
• OS Version: Windows_NT x64 6.1.7601
• Extensions:

Also the same result with today's VS Code Insiders build.

According to the documentation for TextMate scope selectors, VSCode supports the syntax for excluding matching scopes:

entity.name.method - source.java matches all scopes that start with entity.name.method but not if a parent scope matches source.java

This functionality is used in at least one built-in theme that I could find:
https://github.com/Microsoft/vscode/blob/c00bdb74ee665cccfc5c4e41520893bb19ef61e5/extensions/theme-monokai/themes/monokai-color-theme.json#L316

But it seems that this syntax makes the selector with - in it invalid, and VSCode doesn't apply the given rule to anything at all.

Steps to Reproduce:

1. Put this rule for syntax highlighting in the settings. Confirm that comments turn yellow at least in some files.

{
    "editor.tokenColorCustomizations": {
        "textMateRules": [
            {
                "scope": "comment",
                "settings": {
                    "foreground": "#FFFF00"
                }
            }
        ]
    }
}

2. Change the line with the scope selector to:
   "scope": "comment - source.js",
   Expected result: comments that changed their color after step 1 remain yellow in all files except in .js.
   Actual result: all comments reset to a color defined by the current theme.

Reproduces without extensions: Yes

Copied from original issue: Microsoft/vscode#33802

The issue names no repository files or tests. Start by reproducing the documented comment - source.js selector behavior with editor.tokenColorCustomizations, then locate the scope-selector parsing and matching code and its existing tests. Done means exclusion selectors apply to matching scopes except those under source.js, while ordinary selectors continue to work.