(And yes, I was considering if I should shout in capslock ;) )
I have seen so many fresh starts in Rust that went great during week 1 and 2 and then they collided with the lifetime annotations and then things very quickly got very messy. Let's store a texture pointer created from an OpenGL context based on in-memory data into a HashMap...
impl<'tex,'gl,'data,'key> GlyphCache<'a> {
Yay? And then your hashmap .or_insert_with fails due to lifetime checks so you need a match on the hashmap entry and now you're doing the key search twice and performance is significantly worse than in C.
Or you need to add a library. In C that's #include and a -l linker flag. In Rust, you now need to work through this:
https://doc.rust-lang.org/cargo/reference/manifest.html
to get a valid Cargo.toml. And make sure you don't name it cargo.toml, or stuff will randomly break.