The really awesome thing with rust is how easy it is to make library code which can be called from any language including C and C++ (in most situations) - just as easily as writing a library in C or C++. In some situations even easier than C++.

Thus I can easily see rust replacing C/C++ as the default language for writing 'high performance libraries' in, for use in Ruby/Python/etc. It's usually more similar to what higher level programmers are used to too. You get to use functional code for a start.

But also exactly as in Firefox - libraries / modules can be written in Rust, and then brought in to replace existing C++ code. And I'm sure the ergonomics of this process will improve too.

If a C++ project lead / manager can say, in all honesty: "The x component needs to be re-written for whatever reason - either major refactoring for a desired feature, or performance, or to split out to use in another product. We can either do it in C++, or Rust, and Rust will garentee no new segfaults, we can trivially parellelise a lot of it for improved performance, etc. etc. with no major disadvantages..." then Rust will inevitably grow.

That may be true (I haven’t run the math) but it’s on a very critical path, which is equally important, if not more so, than size.

Heck, if it is that small, but has that big an impact, that’s saying something good too, isn’t it?

WebRender is replacing the most core part of the browser. They are replacing the hardest part, not the stright-line simple code. I suspect that in Firefox, like in many projects, the most modules are relatively peripheral but represent a majority of the LoC.