No maintainer is obligated to not break any part of Linux other than the user space API, there are no stable in-kernel APIs
While Rust in the kernel was experimental, this rule was relaxed somewhat to avoid introducing a barrier for programmers who didn't know Rust, so their work could proceed unimpeded while the experiment ran. In other words, the Rust code was allowed to be temporarily broken while the Rust maintainers fixed up uses of APIs that were changed in C code.
As long as you can detect if/when you break it, you can then either quickly pick up enough to get by (if it's trivial), or you ask around.
Rust contributions to the Linux kernel were made by individuals, and are very obviously subject to the exact same expectations as other kernel contributions. Maintainers have responsibilities, not “communities”.
If they completely replace an API then sure, probably.
But for most changes, like adding a param to a function or a struct, they basically have to learn nothing.
Rust isn't unlike C either. You can write a lot of it in a pretty C like fashion.
I think that with all of the Rust's borrowing rules the statement is very iffy.
Most of the things people stub their toe on in Rust coming from C are already UB in C.
For a given rust function, where you might expect a C programmer to need to interact due to a change in the the C code, most of the lifetime rules will have already been hammered out before the needed updates to the rust code. It's possible, but unlikely, that the C programmer is going to need to significantly change what is being allocated and how.
Yes it does.
The Rust for Linux folks have offered that they would fix up such changes, at least during the experimental period. I guess what this arrangement looks like long term will be discussed ~now.
The weak point will always be the startup time of the JVM which is why you won't see it be used for short lived processes. But for a long lived process like a browser I see no obstacles.
I'm not entirely convinced that Java has much mindshare among system programmers. During my 15 years career in the field I haven't heard "Boy I wish we wrote this <network driver | user-space offload networking application | NIC firmware> in Java" once.
The 'factory factory' era of Java spoiled the language thoroughly for me.
That's not really true. Data races are possible in Java.
Rust controls that quite a bit.