How to return an error from a custom filter

[RedHatter]

If I have custom filter that might produce an anyhow::Error like this

use anyhow::Context;

fn format_datetime(_: &State, value: &Value) -> Result<String, minijinja::Error> {
  let date = value.to_string() + "Z";
  Ok(
    date
      .parse::<DateTime<Local>>()
      .context("Failed to parse date from template")?
      .format("%-m/%d/%Y, %-I:%M %p")
      .to_string(),
  )
  .into()
}

how do I return that error from the custom filter? Or in other words how can I convert an anyhow::Error into a minijinja::Error?

[atsmtat]

You can construct a minijinja::Error using https://docs.rs/minijinja/latest/minijinja/struct.Error.html#method.new by picking an appropriate ErrorKind. InvalidOperation is commonly used in the builtin filters. For example,

date
   .parse::<DateTime<Local>>()
   .map_err(|e| minijinja::Error::new(minijinja::ErrorKind::InvalidOperation, &format!("Failed to parse date from template due to: {e}")))?
   .format(...)

[mitsuhiko]

In addition you can use with_source to hold a reference to a custom error as source which is then returned from Error::source.