askama/testing-no-std/tests/hello-world.rs

#![no_std]

use core::fmt;
use core::str::Utf8Error;

use askama::Template;
use assert_matches::assert_matches;

#[test]
fn hello_world() {
    #[derive(Template)]
    #[template(
        ext = "html",
        source = "Hello {%- if let Some(user) = user? -%} , {{ user }} {%- endif -%}!"
    )]
    struct Hello<'a> {
        user: Result<Option<&'a str>, fmt::Error>,
    }

    let mut buffer = [0; 32];

    let tmpl = Hello { user: Ok(None) };
    let mut cursor = Cursor::new(&mut buffer);
    assert_matches!(tmpl.render_into(&mut cursor), Ok(()));
    assert_eq!(cursor.finalize(), Ok("Hello!"));

    let tmpl = Hello {
        user: Ok(Some("user")),
    };
    let mut cursor = Cursor::new(&mut buffer);
    assert_matches!(tmpl.render_into(&mut cursor), Ok(()));
    assert_eq!(cursor.finalize(), Ok("Hello, user!"));

    let tmpl = Hello {
        user: Ok(Some("<user>")),
    };
    let mut cursor = Cursor::new(&mut buffer);
    assert_matches!(tmpl.render_into(&mut cursor), Ok(()));
    assert_eq!(cursor.finalize(), Ok("Hello, &#60;user&#62;!"));

    let tmpl = Hello {
        user: Err(fmt::Error),
    };
    let mut cursor = Cursor::new(&mut buffer);
    assert_matches!(tmpl.render_into(&mut cursor), Err(askama::Error::Fmt));
}

struct Cursor<'a> {
    data: &'a mut [u8],
    pos: usize,
}

impl<'a> Cursor<'a> {
    fn new(data: &'a mut [u8]) -> Self {
        Self { data, pos: 0 }
    }

    fn finalize(self) -> Result<&'a str, Utf8Error> {
        core::str::from_utf8(&self.data[..self.pos])
    }
}

impl fmt::Write for Cursor<'_> {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        let data = &mut self.data[self.pos..];
        if data.len() >= s.len() {
            data[..s.len()].copy_from_slice(s.as_bytes());
            self.pos += s.len();
            Ok(())
        } else {
            Err(fmt::Error)
        }
    }
}