Comment by pron

This is true. In Java, we have a notion we call "integrity", which is a generalisation of memory safety and includes a host of properties guaranteed by the platform. It includes memory safety, but also things like "a non-public method cannot be called or a non-public field cannot be accessed (even reflectively) by code in another module".

To address the problem that once integrity can be violated anywhere, only global analysis can prove that nothing bad happens, we've done two things:

1. We require the application to explicitly permit any integrity violation by a module; i.e. a library can't allow itself to violate integrity. This is a principle we call "Integrity by Default" (https://openjdk.org/jeps/8305968).

2. We try to minimise the need for potential integrity violations (this is very different from Rust, which requires unsafe even for things like benign write/write races, which are fairly common, and various basic data structures). Over the years we've offered safe replacements for things that used to require Unsafe. In other words, clearly demarcating unsafe code isn't enough if it's needed at all in many situations.

It isn't perfect, of course, as some libraries do require unsafe operations for direct interaction with native code or with memory, but their number has been greatly reduced, and they cannot do this without the application's explicit approval. Interestingly, this has annoyed library authors who want to do unsafe things but don't want to application authors to be alarmed because "we know what we're doing," and it's also annoyed some application authors who want to use such libraries and are forced to explicitly add permissions. But I think that the community, as a whole, has eventually accepted this because the harm done to those who don't care is small (they just need to add the permissions), to those who do care it helps a lot, and because fewer and fewer libraries require "integrity-busting" permissions, many applications need to do absolutely nothing and get important guarantees for free.