Converting to int halts rendering if the input is not a number

[alanwsmith]

Description

I'm reading a variable that's passed in from a content source file. It comes in as text. I convert it to a number with int. The problem is that if the content contains a letter instead of a number the page doesn't render.

Reproduction steps

Here's an example of what I'm seeing:

---
[dependencies]
minijinja = { version = "2.9.0"  }
---

use minijinja::{Environment, Value, context};

fn main() {
  let test_one = Value::from("1");
  let test_two = Value::from(2);
  let test_three = Value::from("a");
  do_output(&test_one);
  do_output(&test_two);
  do_output(&test_three);
}

fn do_output(input: &Value) {
    let mut env = Environment::new();
    env.add_template(
        "example", "{{ input|int }}"
    ).unwrap();
    if let Ok(template) = env.get_template("example") {
        match template.render(context!(input)) {
            Ok(output) => println!("{}", output),
            Err(e) => println!("{}", e)
        }
    }
}

The output is:

1
2
invalid operation: invalid float literal (in example:1)

The input is user generated. I don't have a way to guarantee it's a number.

Additional helpful information:

• Version of minijinja: 2.9.0
• Version of rustc: rustc 1.88.0-nightly (17ffbc81a 2025-04-04)
• Operating system and version: macOS 15.4

What did you expect

My first guess is that the result would be none. Whatever the actual case, I expected the page to render at least something instead of throwing an error at the .render() level that prevents output.

The docs list the return type as Result<Value, Error>. That makes sense, but I'd like to be able to ensure the page renders if an Error occurs (I can handle the presentation issues in the template).

Is there a way to allow that to happen?

[mitsuhiko]

I'm not entirely sure I understand what you are trying to accomplish I have to admit. Are you asking about how to convert the error into a string that can be displayed or are you asking how to get the output that was evaluated and discarded, prior to the error that occurred?

[alanwsmith]

My goal is to prevent int from stopping a .render() if it receives something it can't parse.

Maybe it's better to say I'd like to be able to handle the problem in the template. Getting the error converted into something I can display (or otherwise use in the template) would be perfect.

[mitsuhiko]

You can always register a custom filter that does not error and returns none or something similar if it fails. But that is I think something for you to provide, that does not seem actionable within Jinja. I'm going to convert this into a discussion.

[alanwsmith]

right on. i'll take a look at the custom filter approach