[Issue 17424] Add useful warnings

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17424

--- Comment #3 from Jonathan M Davis <issues.dlang at jmdavisProg.com> ---
(In reply to Eyal from comment #0)
> * Signed/unsigned comparisons

There is talk of making this an error. I don't recall what's currently
preventing it, but there is an open issue on the topic: issue #259

> * Code was determined to be dead (will never be executed)

Warinng about unreachable code is actually one of the few warnings that we
actually do have.

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