Custom panic hook for RMC including current item

[avanhatt]

Description of changes:

When RMC panics currently, you get the standard Rustc panic message, including a link to their bug reporting. Add a custom panic hook with our bug template link and include the current codegen item (usually function) causing the problem.

Example panic now:

   Compiling libc v0.2.93
thread 'rustc' panicked at 'oops', compiler/rustc_codegen_llvm/src/gotoc/mod.rs:208:9
stack backtrace:
   0: std::panicking::begin_panic
             at /home/ubuntu/rmc/library/std/src/panicking.rs:541:12
…

note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.55.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -Z force-unstable-if-unmarked -Z trim-diagnostic-paths=no -Z codegen-backend=gotoc -C embed-bitcode=no -C debuginfo=2 --crate-type lib

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
end of query stack

[RMC] current codegen item: codegen_static: DefId(0:8806 ~ core[e967]::fmt::num::DEC_DIGITS_LUT)

RMC unexpectedly panicked during code generation.

If you are seeing this message, please file an issue here instead of on the Rust compiler: https://github.com/model-checking/rmc/issues/new?labels=bug&template=bug_report.md
error: could not compile `core`

To learn more, run the command again with --verbose.
warning: build failed, waiting for other jobs to finish...
error: build failed

Resolved issues:

Resolves #287

Call-outs:

Unfortunately, we can't use the same approach Cranelift uses to remove rustc's bug report link, since that would introduce a circular dependency on rustc_driver. Adding a comment explaining that.

Testing:

• How is this change tested?

Manually introducing panics.

• Is this a refactor change?

No.

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[danielsn]

Is there a more descriptive name to use here?

[avanhatt]

Changed, thanks!

[danielsn]

We should reset the item at the end, to avoid spuriously having a set item if there is none. We could use a RAII pattern, tho that might be overkill

[avanhatt]

Done, reset after both loops.

[avanhatt]

Not sure what exactly RAII would look like here, feel free to follow up if this change is not sufficient?