Helper arguments starting with a number are split in two parts

[jdesgats]

When a helper parameter starts with a number, but contain something else after, it will be split at the first non-digit character.

For example {{helper 100_000}} will result in an agument sequence of [PathAndJson { relative_path: None, value: Constant(Number(100)) }, PathAndJson { relative_path: Some("_000"), value: Missing }]

I would expect one of:

• String "100_000"
• Number 100000
• Syntax error

But truncating here seems like a bug.

Full example:

use std::collections::BTreeMap;
use handlebars::{Handlebars, RenderContext, Helper, Context, JsonRender, HelperResult, Output};

fn echo_helper (h: &Helper, _: &Handlebars, _: &Context, rc: &mut RenderContext, out: &mut dyn Output) -> HelperResult {
    println!("params={:?}", h.params());
    let param = h.param(0).unwrap();
    out.write(param.value().render().as_ref())?;
    Ok(())
}

fn main() {
  // create the handlebars registry
  let mut handlebars = Handlebars::new();
  handlebars.register_helper("echo", Box::new(echo_helper));

  // register the template. The template string will be verified and compiled.
  let source = "amount: {{echo 100_000}}";
  assert!(handlebars.register_template_string("t1", source).is_ok());

  // Prepare some data.
  //
  // The data type should implements `serde::Serialize`
  let data: BTreeMap<String, String> = BTreeMap::new();
  assert_eq!(handlebars.render("t1", &data).unwrap(), "amount: 100_000");
}

Output with handlebars-rust 4.0.1:

params=[PathAndJson { relative_path: None, value: Constant(Number(100)) }, PathAndJson { relative_path: Some("_000"), value: Missing }]
thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `"amount: 100"`,
 right: `"amount: 100_000"`', src/main.rs:24:3
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[sunng87]

it seems the underscore separator in number literal is a new feature introduced recently and is not supported by some json parsers and handlebarsjs language. We will hold the support for now.

However as you found out, there is issue with our parser when parsing parameters of helpers. This is also related to #443 . I will attempt to fix it in future.

[jdesgats]

Thank yo for your reply. To be clear, I am not expecting the number to be parsed correctly (although in my case of rendering TOML, it would make my life easier 😃). I managed to work around the problem by passing a constant string {{helper "1_000"}} and checking in the helper I have a string parameter (to catch cases where I forget quotes), it works well and I'm happy keeping it that way.

From what I tested with HandlebarsJS it would render the context variable if it exists, which is also what handlebars-rust would do without invoking a helper.

I tested the following template rendered with a context {"1_000": "value"}:

existing:     direct='{{1_000}}' echo='{{echo 1_000}}'
non existing: direct='{{2_000}}' echo='{{echo 2_000}}'

With the original JS handlebars, I get:

existing:     direct='value' echo='value'
non existing: direct='' echo=''

With handlebars-rust, I get:

existing:     direct='value' echo='1'
non existing: direct='' echo='2'

So I guess the right thing to in this case is to try to resolve the "number" as a variable name (even if having such variable names is a bit silly), and fail or not depending on the strict mode.