The first parts of the module system we’ll cover are packages and crates.
A crate is the smallest amount of code that the Rust compiler considers at a time. Even if you run rustc rather than cargo and pass a single source code file (as we did all the way back in the “Writing and Running a Rust Program” section of Chapter 1), the compiler considers that file to be a crate. と、いう具合で以下だいぶ丁寧に解説してる。 パッケージにはa library crateとあるから一つだけなの？とChatGPTに尋ねたら複数入ることもあると断言されたけど。
