# Askama
[](https://crates.io/crates/askama)
[](https://travis-ci.org/djc/askama)
[](https://codecov.io/gh/djc/askama)
Askama implements a template rendering engine based on Jinja.
It generates Rust code from your templates at compile time
based on a user-defined `struct` to hold the template's context.
See below for an example, or read [the documentation][docs].
**"Pretty exciting. I would love to use this already."** --
[Armin Ronacher][mitsuhiko], creator of Jinja
### Feature highlights
* Construct templates using a familiar, easy-to-use syntax
* Benefit from the safety provided by Rust's type system
* Template code is compiled into your crate for optimal performance
* Templates only convert your data as needed
* Templates can access your Rust types directly, according to Rust's
privacy rules
* Debugging features to assist you in template development
* Templates must be valid UTF-8 and produce UTF-8 when rendered
* Works on stable Rust
### Supported in templates
* Template inheritance
* Basic loops and if/else if/else statements
* Whitespace suppressing with '-' markers
* Some built-in filters
It's still early for Askama, so there are some limitations:
* Only a small number of built-in template filters have been implemented
* User-defined template filters are not supported yet
* Debugging template problems can be tricky
All feedback welcome. Feel free to file bugs, requests for documentation and
any other feedback to the [issue tracker][issues] or [tweet me][twitter].
Many thanks to [David Tolnay][dtolnay] for his support in improving Askama.
[docs]: https://docs.rs/askama
[mitsuhiko]: http://lucumr.pocoo.org/
[issues]: https://github.com/djc/askama/issues
[twitter]: https://twitter.com/djco/
[dtolnay]: https://github.com/dtolnay
How to get started
------------------
First, add the following to your crate's `Cargo.toml`:
```toml
# in section [package]
build = "build.rs"
# in section [dependencies]
askama = "0.1"
askama_derive = "0.1"
# in section [build-dependencies]
askama = "0.1"
```
Because Askama will generate Rust code from your template files,
the crate will need to be recompiled when your templates change.
This is supported by adding a build script, `build.rs`, to your crate.
It needs askama as a build dependency:
```rust
extern crate askama;
fn main() {
askama::rerun_if_templates_changed();
}
```
Now create a directory called `templates` in your crate root.
In it, create a file called `hello.html`, containing the following:
```
Hello, {{ name }}!
```
In any Rust file inside your crate, add the following:
```rust
#[macro_use]
extern crate askama; // for the Template trait and custom derive macro
use askama::Template; // bring trait in scope
#[derive(Template)] // this will generate the code...
#[template(path = "hello.html")] // using the template in this path, relative
// to the templates dir in the crate root
struct HelloTemplate<'a> { // the name of the struct can be anything
name: &'a str, // the field name should match the variable name
// in your template
}
fn main() {
let hello = HelloTemplate { name: "world" }; // instantiate your struct
println!("{}", hello.render()); // then render it.
}
```
You should now be able to compile and run this code.
Review the [test cases] for more examples.
[test cases]: https://github.com/djc/askama/tree/master/testing
Debugging and troubleshooting
-----------------------------
You can view the parse tree for a template as well as the generated code by
changing the `template` attribute item list for the template struct:
```rust
#[derive(Template)]
#[template(path = "hello.html", print = "all")]
struct HelloTemplate<'a> { ... }
```
The `print` key can take one of four values:
* `none` (the default value)
* `ast` (print the parse tree)
* `code` (print the generated code)
* `all` (print both parse tree and code)
The parse tree looks like this for the example template:
```
[Lit("", "Hello,", " "), Expr(WS(false, false), Var("name")),
Lit("", "!", "\n")]
```
The generated code looks like this:
```rust
#[allow(dead_code, non_camel_case_types)]
impl<'a> askama::Template for HelloTemplate<'a> {
fn render_to(&self, writer: &mut std::fmt::Write) {
writer.write_str("Hello,").unwrap();
writer.write_str(" ").unwrap();
writer.write_fmt(format_args!("{}", self.name)).unwrap();
writer.write_str("!").unwrap();
writer.write_str("\n").unwrap();
}
}
```
