Better minijinja Error Messages

May 2024

Add debug to the Cargo.toml dependency
Use :# in the error message strings

---
[dependencies]
minijinja = { version= "2.12.0", features = ["debug", "loader"] }
---

use minijinja::{Environment, context};


fn main() {
    let mut env = Environment::new();
    env.set_debug(true);
    env.add_template_owned(
        "hello", "{% include 'asdf' %}".to_string()
    ).unwrap();
    let template = env.get_template("hello").unwrap();
    match template.render(context!(name => "World")) {
      Ok(output) => println!("{}", output),
      Err(err) => {
        eprintln!("{}", error_html(&err));
      }
    }
}

pub fn error_text(err: &minijinja::Error) -> String { 
    let mut output = vec!["A MiniJinja error occurred\n".to_string()];
    output.push(format!("Could not render template:\n{:#}", err));
    let mut err = &err as &dyn std::error::Error;
    while let Some(next_err) = err.source() {
        output.push(format!("\ncaused by:\n{:#}", next_err));
        err = next_err;
    }
    output.join("\n")
}


pub fn error_html(err: &minijinja::Error) -> String {
  let mut output = vec![
    r#"<html><head><style>body { background-color: black; color: goldenrod; }</style></head><body><pre>"#.to_string()
  ];
  output.push(
    "A MiniJinja error occurred\n".to_string(),
  );
  output.push(format!(
    "Could not render template:\n{:#}</p>",
    err
  ));
  let mut err = &err as &dyn std::error::Error;
  while let Some(next_err) = err.source() {
    output.push(format!(
      "\ncaused by:\n{:#}",
      next_err
    ));
    err = next_err;
  }
  output.push("</pre></body></html>".to_string());
  output.join("\n")
}

Output:

<html><head><style>body {{ background-color: black; color: goldenrod; }}</style></head><body><pre>
A MiniJinja error occurred

Could not render template:
template not found: tried to include non-existing template "asdf" (in hello:1)
------------------------------------ hello ------------------------------------
   1 > {% include 'asdf' %}
     i    ^^^^^^^^^^^^^^ template not found
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
No referenced variables
-------------------------------------------------------------------------------</p>
</pre></body></html>

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