scope! could limit itself to literals or &'static str s to discourage misuse

[MaulingMonkey]

One of the very first scopes I tried was:

scope!("I/O", format!("class {}", file.name()));

Suffice it to say it didn't work terribly well when evaluated exactly once:

microprofile-rust/src/lib.rs

Lines 189 to 196 in 2746d44

	($group_name:expr, $scope_name:expr, $color:expr) => {
	{
	static mut TOKEN : u64 = 0;
	static INIT: std::sync::Once = std::sync::Once::new();
	unsafe{
	INIT.call_once(||{
	let group = std::ffi::CString::new($group_name).unwrap();
	let scope = std::ffi::CString::new($scope_name).unwrap();

Of course, this is a reasonable and common optimization for flamegraphing profilers, so I wasn't too terribly confused. That said, there's a a couple of options to help prevent this footgun. One would be to change the macro parameters to limit them to literals:

($group_name:literal, $scope_name:literal, $color:literal) => {

Possibly combined with concat! to append '\0's at compile time instead of at runtime:

concat!($group_name, "\0")

Or to encourage a static lifetime:

let group : &'static str = $group_name;
let scope : &'static str = $scope_name;
let group = std::ffi::CString::new(group).unwrap(); 
let scope = std::ffi::CString::new(scope).unwrap(); 

Which is still defeatable with Box::leak(Box::new(format!("look ma, {}!", "dynamic again"))), but at least you have to work for it, and the end user will hopefully question why they have to do such a thing ;)