You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mod.rs
    path of file: ./repos/handlebars-rust/src/helpers
    
    the code of the file until where you have to start completion: use crate::context::Context;
use crate::error::{RenderError, RenderErrorReason};
use crate::json::value::ScopedJson;
use crate::output::Output;
use crate::registry::Registry;
use crate::render::{do_escape, Helper, RenderContext};

pub use self::helper_each::EACH_HELPER;
pub use self::helper_if::{IF_HELPER, UNLESS_HELPER};
pub use self::helper_log::LOG_HELPER;
pub use self::helper_lookup::LOOKUP_HELPER;
pub use self::helper_raw::RAW_HELPER;
pub use self::helper_with::WITH_HELPER;

/// A type alias for `Result<(), RenderError>`
pub type HelperResult = Result<(), RenderError>;

/// Helper Definition
///
/// Implement `HelperDef` to create custom helpers. You can retrieve useful information from these arguments.
///
/// * `&Helper`: current helper template information, contains name, params, hashes and nested template
/// * `&Registry`: the global registry, you can find templates by name from registry
/// * `&Context`: the whole data to render, in most case you can use data f
    
    fn test_helper_for_subexpression() {
        let mut handlebars = Registry::new();
        assert!(handlebars
            .register_template_string("t2", "{{foo value=(bar 0)}}")
            .is_ok());

        handlebars.register_helper(
            "helperMissing",
            Box::new(
                |h: &Helper<'_>,
                 _: &Registry<'_>,
                 _: &Context,
                 _: &mut RenderContext<'_, '_>,
                 out: &mut dyn Output|
                 -> Result<(), RenderError> {
                    write!(out, "{}{}", h.name(), h.param(0).unwrap().value())?;
                    Ok(())
                },
            ),
        );
        handlebars.register_helper(
            "foo",
            Box::new(
                |h: &Helper<'_>,
                 _: &Registry<'_>,
                 _: &Context,
                 _: &mut RenderContext<'_, '_>,
                 out: &mut dyn Output|
                 -> Result<(), RenderError> {
                    write!(out, "{}", h.hash_get("value").unwrap().value().render())?;
                    Ok(())
                },
            ),
        );

        let mut data = BTreeMap::new();
        // handlebars should never try to lookup this value because
        // subexpressions are now resolved as string literal
        data.insert("bar0".to_string(), true);

        let r2 = handlebars.render("t2", &data);

        assert_eq!(r2.ok().unwrap(), "bar0".to_string());
    }