According to the blog post (https://fishshell.com/blog/rustport/#fn:formatting):

> A lot of the increase in line count can be explained by rustfmt’s formatting, as it likes to spread code out over multiple lines [...] The rest is additional features. Also note that our Rust code is in some places a straight translation of the C++, and fully idiomatic Rust might be shorter.

Rust, IMO is a noisy language. So not surprising it took more lines.

Having to handle every case of every branch also probably balloons line count.

Efficient LOC is not a goal of rust at all anyway.

Rust code defenitely takes more space with default formatter settings if you use functional paradigms. Every chained function call in many cases is one extra line. Default line width is not much anyway. Also if you handle all return types, lines will add up.

Since there are quite many contributors, it can be difficult to introduce some advanced macro requirements for the project, which could reduce the code.

Beyond what others have said about superficial things like laying out code differently, remember that Rust encodes memory-safety-related information in types, function signatures etc that might not exist at all in a C/C++ "we hope you do it right, or it's UB" codebase.

Also, here's a code size tracker that counts tokens not lines, which is a better measure: https://github.com/rrethy/tcount

First experiences with QEMU suggest ~10% more lines of code.

Not surprising to me. While learning Rust, I rewrote in Rust several existing programs I had written in C++ and all of them were longer with default formatting.