According to that blog post (https://security.googleblog.com/2024/09/eliminating-memory-s...), the vulnerability density for 5 year old code in Android is 7.4x lower than for new code. If Rust has a 5000 times lower vulnerability density, and if you imagine that 7.4x reduction to repeat itself every 5 years, you would have to "wait" (work on the code) for... about 21 years to get down to the same vulnerability density as new Rust code has. 21 years ago was 2004. Android (2008) didn't even exist yet.

I also feel like this is good advice when making a language shift, or any _other_ shift, even a stylistic one.

A lot of my coworkers get in this situation where, when a change in direction is made, they feel like we have to stuff the roadmap with work to rewrite everything. That work is... 0 value, in most cases, unless the decision we have made is intended to directly solve an issue in the existing code.

Many times I find that if you just do new work in the new thing, you'll "naturally" prioritize rewriting at the right rate. When we do it that way, we end up replacing, rather than rewriting, those legacy systems, which avoids the pitfall of trying to reproduce prior behavior, down to the bugs it may have had.

>So it makes more sense to write new code in Rust than to rewrite old code in Rust.

This is a general result regardless of what language you're talking about (unless you're really downgrading to assembly or something crazy). This of course presumes that the overall Rust (or other new language) situation is better than the existing one. It's not generally.

The blog post has a number of issues, including mixing C and C++. And Android C++ source code is often filled with C-style code, especially the older the code, and is not always that good in several aspects.

As an example, from https://android.googlesource.com/device/generic/trusty/+/c3f...

Many of the files in that commit have a lot of C-style code, yet are classified as C++. C and C++ are very different programming languages, and memory safety is arguably significantly easier to achieve in practice in C++ than in C, yet in the blog post, C++ is blamed for C-style code, and C and C++ are not differentiated.

Compare and contrast with https://android.googlesource.com/device/generic/goldfish/+/d... . That source code file has much more modern C++. Though even then, it contains goto, and modern C++ code reviews would normally not accept goto in my experience. I do not understand what Google Android is doing when its developers are using goto. Could they not have used lambdas in those places where they are using goto? The mixture of std::string_view and goto, modern and yuck, is disconcerting.

On a different topic, how much of the new Rust code is vendored dependencies? Is Fuchsia included?

Maybe the real value for Google Android that Rust holds, is that it mostly prevents C-style code from being written. And Rust does not support goto, and while I think an argument could be made that goto is OK to include in a toolbox, its usage should be very, very, very, very rare. Why does somewhat modern Google Android C++ allow goto?

I am not impressed by Google Android's C++ code quality. Are Google Android developers, independent of language, significantly below average?

C++ does have baggage, cruft and issues. But having strange C++ code (like goto) and also blaming C++ for C-style code, does not help paint an honest and accurate image. And if Google Android's C++ code review process accepts goto willy-nilly, I do not consider Google Android to be at all credible on any subject related to code quality, memory safety and security in any programming language.