Any way to add custom jobs?

[jonasgeiler]

I'm pretty new to Rust and wanted to write a custom OXVG Visitor to extract the width/height dimensions from the SVG, along with all other the optimizations.
I think I wrote a pretty okay Visitor implementation, but now I am struggling to actually have it run my custom Visitor or job, because I don't seem to have any way to extend the Jobs struct of the oxvg_optimiser. But maybe I've missed something out of inexperience.

What would be the best way to run my Visitor along with all the built-in ones?
Is there currently even a way to do that?

Here is my custom Visitor implementation:

use std::cell::RefCell;
use oxvg_ast::{
    element::Element as ElementTrait,
    visitor::{Context, ContextFlags, Info, PrepareOutcome, Visitor}
};
use serde::{Deserialize, Serialize};
use tsify::Tsify;

#[derive(Tsify, Deserialize, Serialize, Debug, Clone)]
#[serde(transparent)]
/// Extracts the SVG's width and height from the `width`/`height` or `viewBox` attribute on `<svg>`.
/// Based on
/// https://github.com/noahbald/oxvg/blob/d8fc238617d043969dc2af4395c8a53298e65c42/crates/oxvg_optimiser/src/jobs/remove_view_box.rs,
/// https://github.com/noahbald/oxvg/blob/d8fc238617d043969dc2af4395c8a53298e65c42/crates/oxvg_optimiser/src/jobs/remove_dimensions.rs
pub struct ExtractDimensions(pub RefCell<Option<(f64, f64)>>);

impl<'arena, E: ElementTrait<'arena>> Visitor<'arena, E> for ExtractDimensions {
    type Error = String;

    fn element(
        &self,
        element: &mut E,
        _context: &mut Context<'arena, '_, '_, E>,
    ) -> Result<(), Self::Error> {
        // TODO: Traverse the tree and find the root <svg> element, then extract the width and height from the attributes.
        //       See: https://github.com/noahbald/oxvg/blob/d8fc238617d043969dc2af4395c8a53298e65c42/crates/oxvg_optimiser/src/jobs/remove_view_box.rs
        //       See: https://github.com/noahbald/oxvg/blob/d8fc238617d043969dc2af4395c8a53298e65c42/crates/oxvg_optimiser/src/jobs/remove_dimensions.rs

        // TODO: Check if root
        if element.prefix().is_some() || element.local_name().as_ref() != "svg" {
            return Ok(());
        }

        // Already extracted
        if self.0.borrow().is_some() {
            return Ok(());
        }

        if let (Some(width_attr), Some(height_attr)) = (
            element.get_attribute_local(&"width".into()),
            element.get_attribute_local(&"height".into()),
        ) {
            if let (Ok(width), Ok(height)) = (
                width_attr.as_ref().parse::<f64>(),
                height_attr.as_ref().parse::<f64>(),
            ) {
                *self.0.borrow_mut() = Some((width, height));
                return Ok(());
            }
        }

        if let Some(view_box_attr) = element.get_attribute_local(&"viewBox".into()) {
            let mut nums = Vec::with_capacity(4);
            nums.extend(SEPARATOR.split(view_box_attr.as_ref()));
            if nums.len() == 4 {
                if let (Ok(width), Ok(height)) = (
                    nums[2].parse::<f64>(),
                    nums[3].parse::<f64>(),
                ) {
                    *self.0.borrow_mut() = Some((width, height));
                    return Ok(());
                }
            }
        };

        Ok(())
    }
}

lazy_static! {
    pub static ref SEPARATOR: regex::Regex = regex::Regex::new(r"[ ,]+").unwrap();
}

[noahbald]

Hey Jonas, there's currently no way to include your own jobs as parts of the set of Jobs, however you can still run your visitor alongside it.

You should be able to do something like the following (note I haven't checked if this compiles)

let mut jobs = Jobs::default();
let arena = typed_arena::Arena::new();
let dom = parse(
    r#"<svg xmlns="http://www.w3.org/2000/svg">
        test
    </svg>"#,
    &arena,
)
.unwrap();
let info = Info::<Element>::new(&arena);

// You can run your own jobs before/after `Jobs`.
let extract_dimensions = ExtractDimentions::new();
extract_dimensions.start(&mut Element::from_parent(dom.clone()), &info, None); // `start` as a method of the `Visitor` trait
// Run jobs as usual
jobs.run(&dom, &info).unwrap();
// Serialize once done
dom.serialize_with_options(Options::default()).unwrap();

It looks like your visitor is just extracting information, so you could run the visitor by itself if that makes more sense for you.

Oxvg is still pretty new as a project, so feel free to make some suggestions on how we can improve the api for you

[jonasgeiler]

Yeah I ended up writing a CustomJobs struct which copies and does the same as the Jobs struct but only with my custom ExtractDimensions instead of all optimizations. It does pretty much what you've suggested here and seems to work alright!
I do think however that having a built-in way to add custom jobs would be pretty useful, similar to how SVGO allows adding custom plugins.