Arguments::as_str allows code to handle argument-less fmt::Arguments like format_args!("literal") specially by not pulling in any formatting code.

We should investigate if we can improve format_args!("hello: {}", "literal") to result in the same trivial fmt::Arguments as format_args!("hello: literal"), such that any .as_str()-based optimizations are also available for it.

That could also make things like panic!("{}", "message"); work with const_panic, removing the need for panic!(CONST_STR).

This makes panic!("hello") exactly as cheap (and const) as panic!("{}", "hello"), which is also important for #78088 to make sure there are no downsides to its suggestions.

It'd also reduce the need for using concat!(..), since it'd no longer be less efficient to add a {} placeholder to concat literals in a formatting string instead.

As a bonus: format_args!("a: {}", format_args!("b: {}", ..)) could maybe also improved to produce the same as format_args!("a: b: {}", ..).

Assigning to myself to investigate some time Soon™.