> But if they change a few lines in the actual project and compile again it would be near instant.
If it’s a big project and the lines you are changing are in something that is being used many other places then the rebuild will still take a little while. (30 seconds or a minute, or more, depending on the size of the project.)
Likewise, if you work on things in different branches you may need to wait more when you switch branch and work on something there.
Also if you switch between Rust versions you need to wait a while when you rebuild your project.
I love Rust, and I welcome everything that is being done to bring the compile times down further!
For the branch-switching usecase you might get some milage out of sccache [1]. For local storage it's just one binary and two lines of configuration to have a cache around rustc, so it's worth testing out.