Support linting JavaScript vars in clj-kondo

[mjarus007]

• I have read the Clojure etiquette and will respect it when communicating on this platform.

Is your feature request related to a problem? Please describe.
In our company, we want to create a wrapper around js/fetch that will add standard instrumentation to the request headers. So, we'd like to discourage the use of js/fetch directly but rather show a linting error, saying "instead of js/fetch use web.http/js-fetch". However, clj-kondo does not currently support linting JavaScript vars and so linters such as discouraged-var and custom hooks cannot solve this problem. For example,

:discouraged-var
{js/fetch {:message "Use web.http/js-fetch instead"}
web.http/js-fetch' {:message "Use web.http/js-fetch instead"}}

web.http/js-fetch' shows a linting error as expected, however, js/fetch does not.

Describe the solution you'd like
A clear and concise description of what you want to happen.

I would like to be able to show a linting error when js/fetch is used by using code like this,

:discouraged-var
{js/fetch {:message "Use web.http/js-fetch instead"}}

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

• I tried the discouraged-var linter
• I've tried custom hooks
• I even tried using a regex with namespace groups

:ns-groups [{:pattern "js"
              :name js}]

[borkdude]

This already works today if you add:

:linters {:unresolved-namespace {:exclude [js]}

to your config:

$ clj -M:clj-kondo/dev --lint - --lang cljs --config '{:linters {:unresolved-namespace {:exclude [js]} :discouraged-var {js/fetch {:message "Use web.http/js-fetch instead"}}}}' <<< 'js/fetch'
<stdin>:1:1: warning: Use web.http/js-fetch instead

I'll make it work without that config though.