Add macro

[sffc]

When using TinyStr, I find that I often want to write strings that should be statically compiled to a TinyStr. Instead, I have to pick between parsing the strings into TinyStr at runtime, or hard-coding the bits into my source file. It would be much nicer if I could do

tiny_str_4!("root");

and have that automatically compile to the TinyStr4 representation of that string (or fail to compile if the string is invalid).

[zbraniecki]

Ehh, yeah, I also would love to be able to construct them from str. I wish the const functions were advanced enough to give us that for free, but we're not there yet.

Pending:

• Tracking issue for &mut T in const contexts (const_mut_refs) rust-lang/rust#57349
• [tracking issue] dereferencing raw pointers inside constants (const_raw_ptr_deref) rust-lang/rust#51911

I guess until then we could add tinystr-macros crate that would hold the relevant proc-macros.

[sffc]

If it works, a compromise might be a macro_rules! with a signature such as

checked_tiny_str_4!(0x746F6F72, "root");

Inside the macro, you create a TinyStr using new_unchecked, and then const_assert! that the dereferenced TinyStr equals the string.