There already is a Rust web engine, it's called Servo, and it's currently being overtaken by the C++ Ladybird project.
Rust is a bad language to write an open source browser in because the hardest problem of building a browser is not security but the number of people you can convince to work on it.
C++ programmers are a dime a dozen, there's a huge number of people who write C++ for 8 hours a day. The Rust community is mostly dabblers like myself.
But ladybird is ditching c++ for swift?
AFAIU they are not ditching C++, they are exploring writing some parts of the engine in Swift using the new C++ interop features in Swift. But a wholesale switch to Swift doesn't seem realistic.
I remember Andreas saying something along those lines in some interview, but seeing their repo[0] doesn't looks like
C++ 64.6%
HTML 22.4%
JavaScript 11.0%
CMake 0.7%
Objective-C++ 0.5%
Swift 0.3%
Other 0.5%
[0] https://github.com/LadybirdBrowser/ladybird
It did seem like an odd decision maybe they thought better of it.
I guess it's just me but after more than 10 years of C++ 8 hours a day I'm happy to never touch it for free
> it's currently being overtaken by the C++ Ladybird project.
Saying a mature engine that you can use today for ~all of the web is being "overtaken" by unreleased pre-alpha software is a strange definition of overtaking.
Ladybird overtook Servo in WPT a few months ago and the gap is only increasing. Servo cannot match the development pace of Ladybird and Ladybird's access to the huge pool of C++ devs is everything to do with that.