`as_mut_str()` unsound?

[Enyium]

Isn't this unsound?

let mut s = CompactString::const_new("test");
s.as_mut_str().make_ascii_uppercase();

It mutates a &'static str without unsafe!

Possible solutions:

• Make as_mut_str() return Option<&mut str> (similar to as_static_str()).
• Make as_mut_str() unsafe.

Other methods may also be affected. Related issue: #326.

Even if this issue rests for a while, the documentation should warn about this.

[Enyium]

Okay, you internally call as_mut_buf(), which handles this using inline_static_str(). I found this post too late, because const_new() didn't exist back then with that name.

I think a note in the documentation for as_mut_str() (and others?) that calling the function will mutate the instance by copying a &'static str first would still be appropriate.