dust_dds_gen: confusing error messages when missing semicolons

[Notgnoshi]

I've spent too long writing Rust that I missed that structs, enums, et al, are terminated with semicolons, so my first draft of the IDL I'm working on was missing them entirely. It turns out they're not required by our internal C++ code generator, so we didn't find the issue early 😅.

The following

struct SomeStruct {}

enum SomeEnum {}

fails to parse with

thread 'enum_annotation' (1792741) panicked at dds_gen/tests/enum_annotation.rs:17:57:
called `Result::unwrap()` on an `Err` value: "Error parsing IDL string:  --> 2:15\n  |\n2 | enum SomeEnum {}\n  |               ^---\n  |\n  = expected fixed_array_size"
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

which is quite confusing, and doesn't point out that the issue is a missing semicolon.

I expect this is quite challenging to address, but I thought I'd at least report my experience. I suspect the answer will be "We're at the mercy of Pest's generated parser" or "There's more value in having our Pest grammar match the OMG grammar than there is in customizing it for better error reporting", both of which I believe are acceptable responses.

I consider this a low priority issue.

[jrebelo]

Definitely not the most intuitive error message. We are indeed at the mercy of Pest's parser but I remember some time back that they were trying to improve the error message generation so maybe it is time to have a look if something has happened.