> The main thing that I use compiling for is to validate little off-by-one things. Like, is substring() exclusive on the second parameter? What about range syntax and the slice operator? What if I wrote + 1 instead of - 1 somewhere, or did < instead of <=?

Rust has a testing facility that can be used for these things. By default, all "example" code that's included as part of a doc comment ends up in the test suite. And because test cases are small and self-contained, they're also very quick to compile.