Errors from retrieving model arguments are swallowed

[hannobraun]

The Fornjot application communicates with the models it loads over an FFI boundary (with Rust code on both sides). This is necessary, because models are compiled to dynamic libraries, and Rust doesn't have a stable ABI. Panics in model code must not cross this FFI boundary, as that would be undefined behavior. Therefore, panics in model code are caught and turned into errors, which are then displayed in the Fornjot application.

There is one hole in the code that is handling this. If a panic occurs in a model's argument handling code (which is generated by fj-proc), it is converted into an error, but then later silently ignored:
https://github.com/hannobraun/Fornjot/blob/ed08c4c8d99d3e146a9a815406e02e276a040d77/crates/fj/src/abi/context.rs#L73

This is not ideal, as that could hide bugs in a highly confusing manner. Instead, the method this is happening in (Context::get_argument) should return a Result instead of an Option and pass that error on. Any downstream code should be adapted as necessary.

Labeling as https://github.com/hannobraun/Fornjot/labels/good%20first%20issue, since this is a pretty localized problem.

[emcloughlin]

I think I will try to tackle this as a first issue. Wish me luck lol

[hannobraun]

Sounds great! Looking forward to what you come up with!

[hannobraun]

This issue is no longer applicable. The affected code has been removed. See A New Direction for context.