[DRAFT] Support for C++ Exceptions

[torrancew]

Fixes #1412

This is an early draft to solicit feedback. It is functional, but there are a couple of implementation details that felt rather clumsy:

• Mapping a user specified qualified name (eg Xapian::Database::add_document) to the mangled representations available during function analysis
• Representing the transformations themselves within the existing machinery (the throwable bit is more or less just bolted on at this phase)

And of course some obvious missing bits like documentation, additional test cases, etc. Let me know what you think about the current approach, and anything you'd like to see improved -- I'm happy to iterate!

This patch introduces a throws! macro, so that individual functions and methods can be marked as throwing an exception. Example usage can be found in the provided unit tests, but generally resembles:

import_cpp! {
    #include "foo.h"
    generate!("do_something")
    throws!("do_something")
}

• CLA signed
• Tests pass
• Appropriate changes to README are included in PR

[adetaylor]

This feels very much along the right lines. In fact you've gone further than I thought you'd do in the initial iteration by tackling the MoveIt TryNew stuff.

Before I land this, I'd want to see:

• Diagnostics if a throws! directive had no effect
• Documentation, obviously
• All existing tests passing (I'll click the Approve and Run button shortly)

Generally speaking this is looking great.

[torrancew]

Thanks!

The test suite is green locally, and the failing tests appear to be the ones I've added. I'm inclined to suspect a difference in my build environment and CI's. I'll dig into that and try to make them a bit more portable, assuming it's correct. Likewise I'll start in on cleaning up the docs. In the mean time, I added a few more test cases, and in the process uncovered (and fixed) support for constructors as well!

[adetaylor]

I appreciate that much of the naming stuff is a bit of a mess, but please do your best to be consistent here with the way other configuration directives are approached.

In byvalue_checker.rs we have:

        let pod_requests = config
            .get_pod_requests()
            .iter()
            .map(|ty| QualifiedName::new_from_cpp_name(ty))
            .collect();

and the comment in new_from_cpp_name suggests this is what you should be using.

[adetaylor]

Slight preference for a single match statement with an arm something like _ if !analysis.throwable => ret_type. (Here and elsewhere). Just to reduce depth of nested statements.