Invoking StableMir::run() on a crate that has any compilation error was
crashing the entire process. Instead, return a `CompilerError` so the
user knows compilation did not succeed.

I believe ICE will also be converted to `CompilerError`.

I'm also adding a return value to the callback, because I think it will
be handy for users (at least it was for my current task of implementing
a tool to validate stable-mir). However, if people disagree,
I can remove that.

Currently we stop compilation, but some users might want to keep going.
This is needed for us to test against rustc tests. Other tools, such as
Kani, also implements parts of their logic as a backend so it is
important for compilation to continue.

clarify safety documentation of ptr::swap and ptr::copy

Closes rust-lang#81005

Add support to return value in StableMIR interface and not crash due to compilation error

Invoking `StableMir::run()` on a crate that has any compilation error was crashing the entire process. Instead, return a `CompilerError` so the user knows compilation did not succeed. I believe ICE will also be converted to `CompilerError`.

I'm also adding a possibility for the callback to return a value. I think it will be handy for users (at least it was for my current task of implementing a tool to validate stable-mir). However, if people disagree, I can remove that.

… r=aliemjay

implied bounds: do not ICE on unconstrained region vars

fixes rust-lang#112832

see tests/ui/implied-bounds/implied-bounds-unconstrained-2.rs for a minimal example showing why this is necessary.

r? types

cc ``@compiler-errors`` ``@aliemjay`` https://rust-lang.zulipchat.com/#narrow/stream/144729-t-types/topic/assoc.20type.20bound.20in.20super.20trait