Alternatively to nimpretty or nimsuggest, there could be a diagnostic message letting code authors just change `var` to `let` or `let` to `const` as they think most helps clarity and their plans for code evolution.
E.g., `var-ness unused` or `run-time-ness unused`. I suspect this is the sort of thing being asked for. Maybe better messages would be "var could be let" or "let could be const" (or I guess the more rare "var could be const"...). Maybe such exists already..I didn't look.
