Empty variables result in errors and default not working?

[Attacler]

liquid-rust version: 0.26.9
rust version: rustc 1.82.0
OS: Windows

If i pass in an empty object but the template tries to read the variable, it will crash.
Reproduction of my issue:

pub fn render_template(template: String, globals: liquid::Object) -> String{
    let template = liquid::ParserBuilder::with_stdlib()
        .build()
        .unwrap()
        .parse(&template)
        .unwrap();

    let output = template.render(&globals).unwrap();

    return output;
}

render_template(
   "Liquid! {{ product_price | default: 2.99 }}".to_string(),
   liquid::Object::new(),
);

The error:

called `Result::unwrap()` on an `Err` value: Error { inner: InnerError { msg: "Unknown variable", user_backtrace: [Trace { trace: None, context: [("requested variable", "product_price")] }], cause: None } }note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Maybe i missed something but shouldent the output be the default value?
As stated on https://liquidjs.com/filters/default.html
Also, if the variable isnt there and default is not provided, shouldent there be nothing at all instead of crashing?

I might be in the wrong, so please correct me if i am!

[jesseditson]

Curious about this as well. Is strict parsing incompatible with the default filter? It seems like they're either mutually exclusive, or the parsing in this implementation is overly strict. I would expect non-defined key access to return an EmptyDrop or Nil, but probably not error.

This behavior, to me, does make sense for deep access - e.g. if I attempt to access foo.bar.baz, where foo is { something: 1}, I would expect an index error, but foo.bar should return an empty value so I can default it using a filter.

[jesseditson]

Seems like this may also be related to #477. FWIW it looks like this is also unresolved in the ruby lib, which and liquidjs implements a lenient_if to special-case default to not be useless with strict_variables on: Shopify/liquid#1404. This issue in turn points to the larger discussion here: Shopify/liquid#1034

[jesseditson]

After going through the related material, it seems like the correct thing to do here is to allow using the default filter for values that are Value::Nil, but not on missing values, which is in fact what this library does.

I'd recommend resolving this in the consuming code, by providing a schema with any values that need defaults. This library doesn't support non-strict_variables mode, so defaulting is up to the consumer.

[jesseditson]

Given the OP's code, these tests pass:

#[test]
    fn render_with_nil() {
        let mut object = liquid::model::Object::new();
        object.insert("product_price".into(), liquid::model::Value::Nil);
        render_template(
            "Liquid! {{ product_price | default: 2.99 }}".to_string(),
            object
         );
    }
    #[test]
    fn render_with_deep_nil() {
        let mut product = liquid::model::Object::new();
        product.insert("price".into(), liquid::model::Value::Nil);
        let mut object = liquid::model::Object::new();
        object.insert("product".into(), product.into());
        render_template(
            "Liquid! {{ product.price | default: 2.99 }}".to_string(),
            object
         );
    }
    #[test]
    #[should_panic(expected = "Unknown variable")]
    fn render_with_empty() {
        render_template(
            "Liquid! {{ product_price | default: 2.99 }}".to_string(),
            liquid::Object::new(),
         );
    }