The rust compiler itself can take as long as 2 hours on a modern laptop if you do a full stage 2 build. I don't think that's what the top poster was talking about though, it sounded like they had a rust toolchain already.

(You know this, but for anyone else reading, don't forget that that doing this compiles LLVM, which is in of itself a massive C++ project, as well as compiling the compiler itself multiple times. That's part of why it would be such an outlier.)

Right. Nested C/C++ dependencies are the only case I can think of where drastically-long compile times are common.

Or maybe someone included Boost?

Sometimes it is just that someone drank the Kool-aid and made everything a template. Then split their code across hundreds of tiny files and did the one big massive include at the top of every file that pulls in everything.