Deprecate `!a == b`

[Lance Bachmeier]

On Tuesday, 13 August 2024 at 10:14:29 UTC, Timon Gehr wrote:
> A bug that crops up now and then in D is that someone negates 
> `a == b` by prepending a `!`. The result is `!a == b`. This 
> parses as `(!a) == b` and will often silently do the wrong 
> thing because negation implies cast to `bool`, and `bool` can 
> be compared with integral types and `enum` members.
>
> I think it would be better for this to give a diagnostic and 
> require explicit parentheses, similar to bitwise operators 
> (where the operator precedence is unintuitive in the other 
> direction).

This should be done. The current behavior isn't likely something 
that's used very often (testing equality of two bools). Breaking 
code isn't a problem because !a == b would fail to compile, and 
it's trivial to fix. Other changes to the language have been more 
annoying while providing less benefit.