Array::map annotate with #[must_use]

[scottmcm]

@dlight

[...] should be marked with something like #[may_ignore]

You might be interested in this recent thread:

Improving the usefulness of `#[must_use]`

I don't have any exact behaviour in mind. I just know three things, People keep asking for must_use on more and more functions -- there's something like 1822 instances in the standard library, based on a quick rg. Most of those have nothing useful to say (unlike, for example, the one on split_off that can point you to use truncate instead, rather than give a generic message) Yet somehow people apparently don't want to turn on unused_results lint that does tell you about every unused result. …