> I don’t think the Rust code could be shorter than the C++ code when converting pretty much line by line, since that leads to C++-style Rust code.

I thought the opposite: header files (and CMakeLists.txt, which was included in the subtotal SLOC) artificially increase C++ SLOC.

> For example idiomatic Rust code can do with less defensive programming due to language features.

Can you show an example in the Rust code where this might be possible? https://github.com/quick-lint/cpp-vs-rust/tree/master/rust