Liquid create your own tag without parameters

---

This is probably the simplest example of extending the Liquid syntax by new tags. I am not sure how usefule is this in the real world as I think the same could be done with the include tag, but this might help understanding how to create more complex tags.

• We need both liquid and liquid-core

examples/liquid/single-tag/Cargo.toml

[package]
name = "parse"
version = "0.1.0"
edition = "2021"

[dependencies]
liquid = "0.26.9"
liquid-core = "0.26.9"

• We need to add the struct implementing our tag (single_tag::SingleTag) to our parser using the tag method.
• Then we can use the {% single %} tag in our template.

examples/liquid/single-tag/src/main.rs

mod single_tag;

fn main() {
    let template = liquid::ParserBuilder::with_stdlib()
        .tag(single_tag::SingleTag)
        .build()
        .unwrap()
        .parse("Liquid: {% single %}")
        .unwrap();

    let globals = liquid::object!({});

    let output = template.render(&globals).unwrap();
    assert_eq!(
        output,
        "Liquid: Single replaced by this string.".to_string()
    );
}

examples/liquid/single-tag/src/single_tag.rs

use std::io::Write;

use liquid_core::error::ResultLiquidReplaceExt;
use liquid_core::Language;
use liquid_core::Renderable;
use liquid_core::Result;
use liquid_core::Runtime;
use liquid_core::{ParseTag, TagReflection, TagTokenIter};

#[derive(Copy, Clone, Debug, Default)]
pub struct SingleTag;

impl TagReflection for SingleTag {
    fn tag(&self) -> &'static str {
        "single"
    }

    fn description(&self) -> &'static str {
        ""
    }
}

impl ParseTag for SingleTag {
    fn parse(
        &self,
        mut arguments: TagTokenIter<'_>,
        _options: &Language,
    ) -> Result<Box<dyn Renderable>> {
        arguments.expect_nothing()?;
        Ok(Box::new(Single))
    }

    fn reflection(&self) -> &dyn TagReflection {
        self
    }
}

#[derive(Debug)]
struct Single;

impl Renderable for Single {
    fn render_to(&self, writer: &mut dyn Write, _runtime: &dyn Runtime) -> Result<()> {
        write!(writer, "Single replaced by this string.").replace("Failed to render")?;
        Ok(())
    }
}

#[cfg(test)]
mod test {
    use super::*;

    use liquid_core::parser;
    use liquid_core::runtime;
    use liquid_core::runtime::RuntimeBuilder;

    fn options() -> Language {
        let mut options = Language::default();
        options
            .tags
            .register("single".to_string(), SingleTag.into());
        options
    }

    #[test]
    fn simple() {
        let options = options();
        let template = parser::parse("{% single %}", &options)
            .map(runtime::Template::new)
            .unwrap();

        let runtime = RuntimeBuilder::new().build();

        let output = template.render(&runtime).unwrap();
        assert_eq!(output, "Single replaced by this string.");
    }
}