I'm in Madrid since Monday, at the third GNOME+Rust hackfest! The OpenShine folks are kindly letting us use their offices, on the seventh floor of a building by the Cuatro Caminos roundabout.
I am very, very thankful that this time everyone seems to be working on developing gnome-class. It's a difficult project for me, and more brainpower is definitely welcome — all the indirection, type conversion, GObject obscurity, and procedural macro shenanigans definitely take a toll on oneself.
I explained how gnome-class works to the rest of the hackfest attendees. I've been writing a document on gnome-class's internals, so the whiteboard was a whirlwind tour through it.
Error messages from the compiler
Antoni Boucher, the author of relm (a Rust crate to write GTK+ asynchronous widgets with an Elm-like model), explained to me how relm manages to present good error messages from the Rust compiler, when the user's code has mistakes. Right now this is in a very bad state in gnome-class: user errors within the invocation of the procedural macro get shown by the compiler as errors at the macro call, so you don't get line number information that is meaningful.
For a large part of the day we tried to refactor bits of gnome-class to do something similar. It is very slightly better now, but this really requires me to sit down calmly, at home, and to fully understand how relm does it and what changes are needed in the syn parser crate to make it easy to present good errors.
I think I'll continue this work at home, as there is a lot of source code to understand: the combinator parsers in syn, the error handling scheme in relm, and the peculiarities of gnome-class.
Further work during the hackfest
Other people working on gnome-class are adding support for GObject properties, inheritance from non-Rust classes, and improving the ergonomics of class-private structures.
I think I'll stop working on error messages for now, and focus instead on either supporting GTypeInterfaces, or completing support for type conversions for methods and signals.
Other happenings in Rust
Paolo Borelli has been porting RsvgState to Rust in librsvg. This is the big structure that holds all the CSS state for SVG elements. This is very meticulous work, and I'm thankful that Paolo is paying good attention to it. Soon we will have all the style machinery for librsvg in Rust, which will make it easier to use the selectors crate from Servo instead of libcroco, as the latter is unmaintained.
Ah, Spanish food. We have been enjoying cheese, jamón, tortilla, pimientos, oxtail stews, natillas, café con leche...
Thanks to OpenShine for hosting the hackfest, and to the GNOME Foundation for sponsoring my travel. And thanks for Alberto Ruiz for putting me up in his house!