Rinja

Rinja 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.

All feedback welcome! Feel free to file bugs, requests for documentation and any other feedback to the issue tracker.

Have a look at our Rinja Playground, if you want to try out rinja's code generation online.

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
• Optional built-in support for Actix, Axum, Rocket, and warp web frameworks
• 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
• Loops, if/else statements and include support
• Macro support
• Variables (no mutability allowed)
• Some built-in filters, and the ability to use your own
• Whitespace suppressing with '-' markers
• Opt-out HTML escaping
• Syntax customization

Getting Started

First, add the following to your crate's Cargo.toml:

# in section [dependencies]
rinja = "0.12.1"

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:

use rinja::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().unwrap()); // then render it.
}

You should now be able to compile and run this code.

Using integrations

To use one of the integrations, with axum as an example:

First, add this to your Cargo.toml instead:

# in section [dependencies]
rinja_axum = "0.4.0"

Then, import from rinja_axum instead of rinja:

#![allow(unused)]
fn main() {
use rinja_axum::Template;
}

This enables the implementation for axum's IntoResponse trait, so an instance of the template can be returned as a response.

For other integrations, import and use their crate accordingly.

Creating Templates

An Rinja template is a struct definition which provides the template context combined with a UTF-8 encoded text file (or inline source, see below). Rinja can be used to generate any kind of text-based format. The template file's extension may be used to provide content type hints.

A template consists of text contents, which are passed through as-is, expressions, which get replaced with content while being rendered, and tags, which control the template's logic. The template syntax is very similar to Jinja, as well as Jinja-derivatives like Twig or Tera.

#![allow(unused)]
fn main() {
#[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
}
}

The template() attribute

Rinja works by generating one or more trait implementations for any struct type decorated with the #[derive(Template)] attribute. The code generation process takes some options that can be specified through the template() attribute. The following sub-attributes are currently recognized:

• path (as path = "foo.html"): sets the path to the template file. The path is interpreted as relative to the configured template directories (by default, this is a templates directory next to your Cargo.toml). The file name extension is used to infer an escape mode (see below). In web framework integrations, the path's extension may also be used to infer the content type of the resulting response. Cannot be used together with source.

  #![allow(unused)]
  fn main() {
  #[derive(Template)]
  #[template(path = "hello.html")]
  struct HelloTemplate<'a> { ... }
  }

• source (as source = "{{ foo }}"): directly sets the template source. This can be useful for test cases or short templates. The generated path is undefined, which generally makes it impossible to refer to this template from other templates. If source is specified, ext must also be specified (see below). Cannot be used together with path.

  #![allow(unused)]
  fn main() {
  #[derive(Template)]
  #[template(source = "Hello {{ name }}")]
  struct HelloTemplate<'a> {
      name: &'a str,
  }
  }

• in_doc (as in_doc = true): please see the section "documentation as template code".

• ext (as ext = "txt"): lets you specify the content type as a file extension. This is used to infer an escape mode (see below), and some web framework integrations use it to determine the content type. Cannot be used together with path.

  #![allow(unused)]
  fn main() {
  #[derive(Template)]
  #[template(source = "Hello {{ name }}", ext = "txt")]
  struct HelloTemplate<'a> {
      name: &'a str,
  }
  }

• print (as print = "code"): enable debugging by printing nothing (none), the parsed syntax tree (ast), the generated code (code) or all for both. The requested data will be printed to stdout at compile time.

  #![allow(unused)]
  fn main() {
  #[derive(Template)]
  #[template(path = "hello.html", print = "all")]
  struct HelloTemplate<'a> { ... }
  }

• block (as block = "block_name"): renders the block by itself. Expressions outside of the block are not required by the struct, and inheritance is also supported. This can be useful when you need to decompose your template for partial rendering, without needing to extract the partial into a separate template or macro.

  #![allow(unused)]
  fn main() {
  #[derive(Template)]
  #[template(path = "hello.html", block = "hello")]
  struct HelloTemplate<'a> { ... }
  }

• escape (as escape = "none"): override the template's extension used for the purpose of determining the escaper for this template. See the section on configuring custom escapers for more information.

  #![allow(unused)]
  fn main() {
  #[derive(Template)]
  #[template(path = "hello.html", escape = "none")]
  struct HelloTemplate<'a> { ... }
  }

• syntax (as syntax = "foo"): set the syntax name for a parser defined in the configuration file. The default syntax , "default", is the one provided by Rinja.

  #![allow(unused)]
  fn main() {
  #[derive(Template)]
  #[template(path = "hello.html", syntax = "foo")]
  struct HelloTemplate<'a> { ... }
  }

• config (as config = "config_file_path"): set the path for the config file to be used. The path is interpreted as relative to your crate root.

  #![allow(unused)]
  fn main() {
  #[derive(Template)]
  #[template(path = "hello.html", config = "config.toml")]
  struct HelloTemplate<'a> { ... }
  }

Documentation as template code

As an alternative to supplying the code template code in an external file (as path argument), or as a string (as source argument), you can also enable the "code-in-doc" feature. With this feature, you can specify the template code directly in the documentation of the template item.

Instead of path = "…" or source = "…", specify in_doc = true in the #[template] attribute, and in the item's documentation, add a code block with the rinja attribute:

#![allow(unused)]
fn main() {
/// Here you can put our usual comments.
///
/// ```rinja
/// <div>{{ lines|linebreaksbr }}</div>
/// ```
///
/// Any usual docs, including tests can be put in here, too:
///
/// ```rust
/// assert_eq!(
///     Example { lines: "a\nb\nc" }.to_string(),
///     "<div>a<br/>b<br/>c</div>"
/// );
/// ```
///
/// All comments are still optional, though.
#[derive(Template)]
#[template(ext = "html", in_doc = true)]
struct Example<'a> {
    lines: &'a str,
}
}

If you want to supply the template code in the comments, then you have to specify the ext argument, too, e.g. #[template(ext = "html")].

Instead of rinja, you can also write jinja or jinja2, e.g. to get it to work better in conjunction with syntax highlighters.

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:

#![allow(unused)]
fn main() {
#[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 resulting output will be printed to stderr during the compilation process.

The parse tree looks like this for the example template:

#![allow(unused)]
fn main() {
[Lit("", "Hello,", " "), Expr(WS(false, false), Var("name")),
Lit("", "!", "\n")]
}

The generated code looks like this:

#![allow(unused)]
fn main() {
impl < 'a > ::rinja::Template for HelloTemplate< 'a > {
    fn render_into(&self, writer: &mut ::std::fmt::Write) -> ::rinja::Result<()> {
        write!(
            writer,
            "Hello, {expr0}!",
            expr0 = &::rinja::MarkupDisplay::from(&self.name),
        )?;
        Ok(())
    }
    fn extension() -> Option<&'static str> {
        Some("html")
    }
}
impl < 'a > ::std::fmt::Display for HelloTemplate< 'a > {
    fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
        ::rinja::Template::render_into(self, f).map_err(|_| ::std::fmt::Error {})
    }
}
}

Configuration

At compile time, Rinja will read optional configuration values from rinja.toml in the crate root (the directory where Cargo.toml can be found). Currently, this covers the directories to search for templates, custom syntax configuration and escaper configuration.

This example file demonstrates the default configuration:

[general]
# Directories to search for templates, relative to the crate root.
dirs = ["templates"]
# Unless you add a `-` in a block, whitespace characters won't be trimmed.
whitespace = "preserve"

Whitespace control

In the default configuration, you can use the - operator to indicate that whitespace should be suppressed before or after a block. For example:

<div>


{%- if something %}
Hello
{% endif %}

In the template above, only the whitespace between <div> and {%- will be suppressed. If you set whitespace to "suppress", whitespace characters before and after each block will be suppressed by default. To preserve the whitespace characters, you can use the + operator:

{% if something +%}
Hello
{%+ endif %}

In this example, Hello will be surrounded with newline characters.

There is a third possibility: in case you want to suppress all whitespace characters except one, you can use ~:

{% if something ~%}
Hello
{%~ endif %}

To be noted, if one of the trimmed characters is a newline, then the only character remaining will be a newline.

If you want this to be the default behavior, you can set whitespace to "minimize".

To be noted: you can also configure whitespace directly into the template derive proc macro:

#![allow(unused)]
fn main() {
#[derive(Template)]
#[template(whitespace = "suppress")]
pub struct SomeTemplate;
}

If you configure whitespace directly into the template derive proc-macro, it will take precedence over the one in your configuration file. So in this case, if you already set whitespace = "minimize" into your configuration file, it will be replaced by suppress for this template.

Custom syntaxes

Here is an example that defines two custom syntaxes:

[general]
default_syntax = "foo"

[[syntax]]
name = "foo"
block_start = "%{"
comment_start = "#{"
expr_end = "^^"

[[syntax]]
name = "bar"
block_start = "%%"
block_end = "%%"
comment_start = "%#"
expr_start = "%{"

A syntax block consists of at least the attribute name which uniquely names this syntax in the project.

The following keys can currently be used to customize template syntax:

• block_start, defaults to {%
• block_end, defaults to %}
• comment_start, defaults to {#
• comment_end, defaults to #}
• expr_start, defaults to {{
• expr_end, defaults to }}

Values must be at least two characters long. If a key is omitted, the value from the default syntax is used.

Here is an example of a custom escaper:

[[escaper]]
path = "::tex_escape::Tex"
extensions = ["tex"]

An escaper block consists of the attributes path and extensions. path contains a Rust identifier that must be in scope for templates using this escaper. extensions defines a list of file extensions that will trigger the use of that escaper. Extensions are matched in order, starting with the first escaper configured and ending with the default escapers for HTML (extensions html, htm, xml, j2, jinja, jinja2) and plain text (no escaping; md, yml, none, txt, and the empty string). Note that this means you can also define other escapers that match different extensions to the same escaper.

Template Syntax

Variables

Top-level template variables are defined by the template's context type. You can use a dot (.) to access variable's attributes or methods. Reading from variables is subject to the usual borrowing policies. For example, {{ name }} will get the name field from the template context, while {{ user.name }} will get the name field of the user field from the template context.

Using constants in templates

You can use constants defined in your Rust code. For example if you have:

#![allow(unused)]
fn main() {
pub const MAX_NB_USERS: usize = 2;
}

defined in your crate root, you can then use it in your templates by using crate::MAX_NB_USERS:

<p>The user limit is {{ crate::MAX_NB_USERS }}.</p>
{% set value = 4 %}
{% if value > crate::MAX_NB_USERS %}
    <p>{{ value }} is bigger than MAX_NB_USERS.</p>
{% else %}
    <p>{{ value }} is less than MAX_NB_USERS.</p>
{% endif %}

Assignments

Inside code blocks, you can also declare variables or assign values to variables. Assignments can't be imported by other templates.

Assignments use the let tag:

{% let name = user.name %}
{% let len = name.len() %}

{% let val -%}
{% if len == 0 -%}
  {% let val = "foo" -%}
{% else -%}
  {% let val = name -%}
{% endif -%}
{{ val }}

Like Rust, Rinja also supports shadowing variables.

{% let foo = "bar" %}
{{ foo }}

{% let foo = "baz" %}
{{ foo }}

For compatibility with Jinja, set can be used in place of let.

Filters

Values such as those obtained from variables can be post-processed using filters. Filters are applied to values using the pipe symbol (|) and may have optional extra arguments in parentheses. Filters can be chained, in which case the output from one filter is passed to the next.

For example, {{ "{:?}"|format(name|escape) }} will escape HTML characters from the value obtained by accessing the name field, and print the resulting string as a Rust literal.

The built-in filters are documented as part of the filters documentation.

To define your own filters, simply have a module named filters in scope of the context deriving a Template impl. Note that in case of name collision, the built in filters take precedence.

Filter blocks

You can apply a filter on a whole block at once using filter blocks:

{% filter lower %}
    {{ t }} / HELLO / {{ u }}
{% endfilter %}

The lower filter will be applied on the whole content.

Just like filters, you can combine them:

{% filter lower|capitalize %}
    {{ t }} / HELLO / {{ u }}
{% endfilter %}

In this case, lower will be called and then capitalize will be called on what lower returned.

Whitespace control

Rinja considers all tabs, spaces, newlines and carriage returns to be whitespace. By default, it preserves all whitespace in template code, except that a single trailing newline character is suppressed. However, whitespace before and after expression and block delimiters can be suppressed by writing a minus sign directly following a start delimiter or leading into an end delimiter.

Here is an example:

{% if foo %}
  {{- bar -}}
{% else if -%}
  nothing
{%- endif %}

This discards all whitespace inside the if/else block. If a literal (any part of the template not surrounded by {% %} or {{ }}) includes only whitespace, whitespace suppression on either side will completely suppress that literal content.

If the whitespace default control is set to "suppress" and you want to preserve whitespace characters on one side of a block or of an expression, you need to use +. Example:

<a href="/" {#+ #}
   class="something">text</a>

In the above example, one whitespace character is kept between the href and the class attributes.

There is a third possibility. In case you want to suppress all whitespace characters except one ("minimize"), you can use ~:

{% if something ~%}
Hello
{%~ endif %}

To be noted, if one of the trimmed characters is a newline, then the only character remaining will be a newline.

Whitespace controls can also be defined by a configuration file or in the derive macro. These definitions follow the global-to-local preference:

1. Inline (-, +, ~)
2. Derive (#[template(whitespace = "suppress")])
3. Configuration (in rinja.toml, whitespace = "preserve")

Two inline whitespace controls may point to the same whitespace span. In this case, they are resolved by the following preference.

1. Suppress (-)
2. Minimize (~)
3. Preserve (+)

Functions

There are several ways that functions can be called within templates, depending on where the function definition resides. These are:

• Template struct fields
• Static functions
• Struct/Trait implementations

Template struct field

When the function is a field of the template struct, we can simply call it by invoking the name of the field, followed by parentheses containing any required arguments. For example, we can invoke the function foo for the following MyTemplate struct:

#![allow(unused)]
fn main() {
#[derive(Template)]
#[template(source = "{{ foo(123) }}", ext = "txt")]
struct MyTemplate {
  foo: fn(u32) -> String,
}
}

However, since we'll need to define this function every time we create an instance of MyTemplate, it's probably not the most ideal way to associate some behavior for our template.

Static functions

When a function exists within the same Rust module as the template definition, we can invoke it using the self path prefix, where self represents the scope of the module in which the template struct resides.

For example, here we call the function foo by writing self::foo(123) within the MyTemplate struct source:

#![allow(unused)]
fn main() {
fn foo(val: u32) -> String {
  format!("{}", val)
}

#[derive(Template)]
#[template(source = "{{ self::foo(123) }}", ext = "txt")]
struct MyTemplate;
}

This has the advantage of being able to share functionality across multiple templates, without needing to expose the function publicly outside of its module.

However, we are not limited to local functions defined within the same module. We can call any public function by specifying the full path to that function within the template source. For example, given a utilities module such as:

#![allow(unused)]
fn main() {
// src/templates/utils/mod.rs

pub fn foo(val: u32) -> String {
  format!("{}", val)
}
}

Within our MyTemplate source, we can call the foo function by writing:

#![allow(unused)]
fn main() {
// src/templates/my_template.rs

#[derive(Template)]
#[template(source = "{{ crate::templates::utils::foo(123) }}", ext = "txt")]
struct MyTemplate;
}

Struct / trait implementations

Finally, we can call methods of our template struct:

#![allow(unused)]
fn main() {
#[derive(Template)]
#[template(source = "{{ foo(123) }}", ext = "txt")]
struct MyTemplate {
  count: u32,
};

impl MyTemplate {
  fn foo(&self, val: u32) -> String {
    format!("{} is the count, {} is the value", self.count, val)
  }
}
}

You can also use self.foo(123), or even Self::foo(self, 123), as you see fit.

Similarly, using the Self path, we can also call any method belonging to a trait that has been implemented for our template struct:

#![allow(unused)]
fn main() {
trait Hello {
  fn greet(name: &str) -> String;
}

#[derive(Template)]
#[template(source = r#"{{ Self::greet("world") }}"#, ext = "txt")]
struct MyTemplate;

impl Hello for MyTemplate {
  fn greet(name: &str) -> String {
    format!("Hello {}", name)
  }
}
}

If you want to call a closure which is a field, you'll need to follow Rust's syntax by surrounding the call with parens:

#![allow(unused)]
fn main() {
#[derive(Template)]
#[template(source = "{{ (closure)(12) }}", ext = "txt")]
struct MyTemplate {
    closure: fn(i32) -> i32,
}
}

Calling functions

If you only provide a function name, rinja will assume it's a method. If you want to call a method, you will need to use a path instead:

{# This is the equivalent of `self.method()`. #}
{{ method() }}
{# This is the equivalent of `self::function()`, which will call the
`function` function from the current module. #}
{{ self::function() }}
{# This is the equivalent of `super::b::f()`. #}
{{ super::b::f() }}

Template inheritance

Template inheritance allows you to build a base template with common elements that can be shared by all inheriting templates. A base template defines blocks that child templates can override.

Base template

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>{% block title %}{{ title }} - My Site{% endblock %}</title>
    {% block head %}{% endblock %}
  </head>
  <body>
    <div id="content">
      {% block content %}<p>Placeholder content</p>{% endblock %}
    </div>
  </body>
</html>

The block tags define three blocks that can be filled in by child templates. The base template defines a default version of the block. A base template must define one or more blocks in order to enable inheritance. Blocks can only be specified at the top level of a template or inside other blocks, not inside if/else branches or in for-loop bodies.

It is also possible to use the name of the block in endblock (both in declaration and use):

{% block content %}<p>Placeholder content</p>{% endblock content %}

Child template

Here's an example child template:

{% extends "base.html" %}

{% block title %}Index{% endblock %}

{% block head %}
  <style>
  </style>
{% endblock %}

{% block content %}
  <h1>Index</h1>
  <p>Hello, world!</p>
  {% call super() %}
{% endblock %}

The extends tag tells the code generator that this template inherits from another template. It will search for the base template relative to itself before looking relative to the template base directory. It will render the top-level content from the base template, and substitute blocks from the base template with those from the child template. Inside a block in a child template, the super() macro can be called to render the parent block's contents.

Because top-level content from the child template is thus ignored, the extends tag doesn't support whitespace control:

{%- extends "base.html" +%}

The above code is rejected because we used - and +. For more information about whitespace control, take a look here.

Block fragments

Additionally, a block can be rendered by itself. This can be useful when you need to decompose your template for partial rendering, without needing to extract the partial into a separate template or macro. This can be done with the block parameter.

#![allow(unused)]
fn main() {
#[derive(Template)]
#[template(path = "...", block = "my_block")]
struct BlockFragment {
    name: String,
}
}

HTML escaping

Rinja by default escapes variables if it thinks it is rendering HTML content. It infers the escaping context from the extension of template filenames, escaping by default if the extension is one of html, htm, or xml. When specifying a template as source in an attribute, the ext attribute parameter must be used to specify a type. Additionally, you can specify an escape mode explicitly for your template by setting the escape attribute parameter value (to none or html).

Rinja escapes <, >, &, ", and ', according to the OWASP escaping recommendations. Use the safe filter to prevent escaping for a single expression, or the escape (or e) filter to escape a single expression in an unescaped context.

#[derive(Template)]
#[template(source = "{{strvar}}")]
struct TestTemplate {
    strvar: String,
}

fn main() {
    let s = TestTemplate {
        strvar: "// my <html> is \"unsafe\" & should be 'escaped'".to_string(),
    };
    assert_eq!(
        s.render().unwrap(),
        "&#x2f;&#x2f; my &lt;html&gt; is &quot;unsafe&quot; &amp; \
         should be &#x27;escaped&#x27;"
    );
}

Control structures

For

Loop over each item in an iterator. For example:

<h1>Users</h1>
<ul>
{% for user in users %}
  <li>{{ user.name|e }}</li>
{% endfor %}
</ul>

Inside for-loop blocks, some useful variables are accessible:

• loop.index: current loop iteration (starting from 1)
• loop.index0: current loop iteration (starting from 0)
• loop.first: whether this is the first iteration of the loop
• loop.last: whether this is the last iteration of the loop

<h1>Users</h1>
<ul>
{% for user in users %}
   {% if loop.first %}
   <li>First: {{user.name}}</li>
   {% else %}
   <li>User#{{loop.index}}: {{user.name}}</li>
   {% endif %}
{% endfor %}
</ul>

If

The if statement essentially mirrors Rust's if expression, and is used as you might expect:

{% if users.len() == 0 %}
  No users
{% else if users.len() == 1 %}
  1 user
{% elif users.len() == 2 %}
  2 users
{% else %}
  {{ users.len() }} users
{% endif %}

If Let

Additionally, if let statements are also supported and similarly mirror Rust's if let expressions:

{% if let Some(user) = user %}
  {{ user.name }}
{% else %}
  No user
{% endif %}

is (not) defined

You can use is (not) defined to ensure a variable exists (or not):

{% if x is defined %}
  x is defined!
{% endif %}
{% if y is not defined %}
  y is not defined
{% else %}
  y is defined
{% endif %}

You can combine conditions with this feature and even use it in expressions:

{% if x is defined && x == "12" && y == Some(true) %}
...
{% endif %}

<script>
// It will generate `const x = true;` (or false is `x` is not defined).
const x = {{ x is defined }};
</script>

Due to proc-macro limitations, rinja can only see the fields of your current type and the variables declared in the templates. Because of this, you can not check if a field or a function is defined:

{% if x.y is defined %}
  This code will not compile
{% endif %}

Match

In order to deal with Rust enums in a type-safe way, templates support match blocks from version 0.6. Here is a simple example showing how to expand an Option:

{% match item %}
  {% when Some with ("foo") %}
    Found literal foo
  {% when Some with (val) %}
    Found {{ val }}
  {% when None %}
{% endmatch %}

That is, a {% match %} block may contain whitespaces (but no other literal content) and comment blocks, followed by a number of {% when %} blocks and an optional {% else %} block.

Like in Rust, the matching is done against a pattern. Such a pattern may be a literal, e.g.

{% match multiple_choice_answer %}
  {% when 3 %} Correct!
  {% else %} Sorry, the right answer is "3".
{% endmatch %}

Or some more complex type, such as a Result<T, E>:

{% match result %}
  {% when Ok(val) %} Good: {{ val }}.
  {% when Err(err) %} Bad: {{ err }}.
{% endmatch %}

Using the placeholder _ to match against any value without capturing the datum, works too. The wildcard operator .. is used to match against an arbitrary amount of items, and the same restrictions as in Rust, e.g. that it can be used only once in a slice or struct:

{% match list_of_ints %}
  {% when [first, ..] %} The list starts with a {{ first }}
  {% when _ %} The list is empty.
{% endmatch %}

The {% else %} node is syntactical sugar for {% when _ %}. If used, it must come last, after all other {% when %} blocks:

{% match answer %}
  {% when Ok(42) %} The answer is "42".
  {% else %} No answer wrong answer?
{% endmatch %}

A {% match %} must be exhaustive, i.e. all possible inputs must have a case. This is most easily done by using proving an {% else %} case, if not all possible values need an individual handling.

Because a {% match %} block could not generate valid code otherwise, you have to provide at least one {% when %} case and/or an {% else %} case.

You can also match against multiple alternative patterns at once:

{% match number %}
  {% when 1 | 4 | 86 %} Some numbers
  {% when n %} Number is {{ n }}
{% endmatch %}

For better interoperability with linters and auto-formatters like djLint, you can also use an optional {% endwhen %} node to close a {% when %} case:

{% match number %}
  {% when 0 | 2 | 4 | 6 | 8 %}
    even
  {% endwhen %}
  {% when 1 | 3 | 5 | 7 | 9 %}
    odd
  {% endwhen %}
  {% else }
    unknown
{% endmatch %}

Referencing and dereferencing variables

If you need to put something behind a reference or to dereference it, you can use & and * operators:

{% let x = &"bla" %}
{% if *x == "bla" %}
Just talking
{% else if x == &"another" %}
Another?!
{% endif %}

They have the same effect as in Rust and you can put multiple of them:

{% let x = &&"bla" %}
{% if *&**x == "bla" %}
You got it
{% endif %}

Include

The include statement lets you split large or repetitive blocks into separate template files. Included templates get full access to the context in which they're used, including local variables like those from loops:

{% for i in iter %}
  {% include "item.html" %}
{% endfor %}

* Item: {{ i }}

The path to include must be a string literal, so that it is known at compile time. Rinja will try to find the specified template relative to the including template's path before falling back to the absolute template path. Use include within the branches of an if/else block to use includes more dynamically.

Expressions

Rinja supports string literals ("foo") and integer literals (1). It supports almost all binary operators that Rust supports, including arithmetic, comparison and logic operators. The parser applies the same operator precedence as the Rust compiler. Expressions can be grouped using parentheses.

{{ 3 * 4 / 2 }}
{{ 26 / 2 % 7 }}
{{ 3 % 2 * 6 }}
{{ 1 * 2 + 4 }}
{{ 11 - 15 / 3 }}
{{ (4 + 5) % 3 }}

The HTML special characters &, < and > will be replaced with their character entities unless the escape mode is disabled for a template, or the filter |safe is used.

Methods can be called on variables that are in scope, including self.

Warning: if the result of an expression (a {{ }} block) is equivalent to self, this can result in a stack overflow from infinite recursion. This is because the Display implementation for that expression will in turn evaluate the expression and yield self again.

Expressions containing bit-operators

In Rinja, the binary AND, OR, and XOR operators (called &, |, ^ in Rust, resp.), are renamed to bitand, bitor, xor to avoid confusion with filter expressions. They still have the same operator precedende as in Rust. E.g. to test if the least significant bit is set in an integer field:

{% if my_bitset bitand 1 != 0 %}
    It is set!
{% endif %}

Type conversion

You can use the as operator in {{ … }} expressions, and {% … %} blocks. It works the same as in Rust, but with some deliberate restrictions:

• You can only use primitive types like i32 or f64 both as source variable type and as target type.
• If the source is a reference to a primitive type, e.g. &&&bool, then rinja automatically dereferences the value until it gets the underlying bool.

Templates in templates

Using expressions, it is possible to delegate rendering part of a template to another template. This makes it possible to inject modular template sections into other templates and facilitates testing and reuse.

#![allow(unused)]
fn main() {
use rinja::Template;
#[derive(Template)]
#[template(source = "Section 1: {{ s1 }}", ext = "txt")]
struct RenderInPlace<'a> {
   s1: SectionOne<'a>
}

#[derive(Template)]
#[template(source = "A={{ a }}\nB={{ b }}", ext = "txt")]
struct SectionOne<'a> {
   a: &'a str,
   b: &'a str,
}

let t = RenderInPlace { s1: SectionOne { a: "a", b: "b" } };
assert_eq!(t.render().unwrap(), "Section 1: A=a\nB=b")
}

Note that if your inner template like SectionOne renders HTML content, then you may want to disable escaping when injecting it into an outer template, e.g. {{ s1|safe }}. Otherwise it will render the HTML content literally, because rinja escapes HTML variables by default.

See the example render in place using a vector of templates in a for block.

Comments

Rinja supports block comments delimited by {# and #}.

{# A Comment #}

Like Rust, Rinja also supports nested block comments.

{#
A Comment
{# A nested comment #}
#}

Recursive Structures

Recursive implementations should preferably use a custom iterator and use a plain loop. If that is not doable, call .render() directly by using an expression as shown below. Including self does not work, see #105 and #220 .

#![allow(unused)]
fn main() {
use rinja::Template;

#[derive(Template)]
#[template(source = r#"
//! {% for item in children %}
   {{ item }}
{% endfor %}
"#, ext = "html", escape = "none")]
struct Item<'a> {
    name: &'a str,
    children: &'a [Item<'a>],
}
}

Macros

You can define macros within your template by using {% macro name(args) %}, ending with {% endmacro %}.

You can then call it with {% call name(args) %}:

{% macro heading(arg) %}

<h1>{{arg}}</h1>

{% endmacro %}

{% call heading(s) %}

You can place macros in a separate file and use them in your templates by using {% import %}:

{%- import "macro.html" as scope -%}

{% call scope::heading(s) %}

You can optionally specify the name of the macro in endmacro:

{% macro heading(arg) %}<p>{{arg}}</p>{% endmacro heading %}

You can also specify arguments by their name (as defined in the macro):

{% macro heading(arg, bold) %}

<h1>{{arg}} <b>{{bold}}</b></h1>

{% endmacro %}

{% call heading(bold="something", arg="title") %}

You can use whitespace characters around =:

{% call heading(bold = "something", arg = "title") %}

You can mix named and non-named arguments when calling a macro:

{% call heading("title", bold="something") %}

However please note than named arguments must always come last.

Another thing to note, if a named argument is referring to an argument that would be used for a non-named argument, it will error:

{% macro heading(arg1, arg2, arg3, arg4) %}
{% endmacro %}

{% call heading("something", "b", arg4="ah", arg2="title") %}

In here it's invalid because arg2 is the second argument and would be used by "b". So either you replace "b" with arg3="b" or you pass "title" before:

{% call heading("something", arg3="b", arg4="ah", arg2="title") %}
{# Equivalent of: #}
{% call heading("something", "title", "b", arg4="ah") %}

Calling Rust macros

It is possible to call rust macros directly in your templates:

{% let s = format!("{}", 12) %}

One important thing to note is that contrary to the rest of the expressions, Rinja cannot know if a token given to a macro is a variable or something else, so it will always default to generate it "as is". So if you have:

#![allow(unused)]
fn main() {
macro_rules! test_macro{
    ($entity:expr) => {
        println!("{:?}", &$entity);
    }
}

#[derive(Template)]
#[template(source = "{{ test_macro!(entity) }}", ext = "txt")]
struct TestTemplate<'a> {
    entity: &'a str,
}
}

It will not compile, telling you it doesn't know entity. It didn't infer that entity was a field of the current type unlike usual. You can go around this limitation by binding your field's value into a variable:

{% let entity = entity %}
{{ test_macro!(entity) }}

Filters

Values such as those obtained from variables can be post-processed using filters. Filters are applied to values using the pipe symbol (|) and may have optional extra arguments in parentheses. Note that the pipe symbol must not be surrounded by spaces; otherwise, it will be interpreted as the BitOr operator. Filters can be chained, in which case the output from one filter is passed to the next.

{{ "HELLO"|lower }}

Rinja has a collection of built-in filters, documented below, but can also include custom filters. Additionally, the json filter is included in the built-in filters, but is disabled by default. Enable it with Cargo features (see below for more information).

Table of contents

• Built-in filters:

  • abs
  • capitalize
  • center
  • deref
  • escape|e
  • filesizeformat
  • fmt
  • format
  • indent
  • join
  • linebreaks
  • linebreaksbr
  • lower|lowercase
  • paragraphbreaks
  • pluralize
  • ref
  • safe
  • title
  • trim
  • truncate
  • upper|uppercase
  • urlencode
  • wordcount

• Optional / feature gated filters:
  json|tojson,

• Custom filters

• HTML-safe types

  • Safe output of custom filters

Built-In Filters

abs

Returns the absolute value.

{{ -2|abs }}

Output:

2

capitalize

Capitalize a value. The first character will be uppercase, all others lowercase:

{{ "hello"|capitalize }}

Output:

Hello

center

Centers the value in a field of a given width:

-{{ "a"|center(5) }}-

Output:

-  a  -

deref

Dereferences the given argument.

{% let s = String::from("a")|as_ref %}
{% if s|deref == String::from("b") %}
{% endif %}

will become:

#![allow(unused)]
fn main() {
let s = &String::from("a");
if *s == String::from("b") {}
}

escape | e

Escapes HTML characters in strings:

{{ "Escape <>&"|e }}

Output:

Escape <>&

Optionally, it is possible to specify and override which escaper is used. Consider a template where the escaper is configured as escape = "none". However, somewhere escaping using the HTML escaper is desired. Then it is possible to override and use the HTML escaper like this:

{{ "Don't Escape <>&"|escape }}
{{ "Don't Escape <>&"|e }}

{{ "Escape <>&"|escape("html") }}
{{ "Escape <>&"|e("html") }}

Output:

Don't Escape <>&
Don't Escape <>&

Escape &lt;&gt;&amp;
Escape &lt;&gt;&amp;

filesizeformat

Returns adequate string representation (in KB, ..) of number of bytes:

{{ 1000|filesizeformat }}

Output:

1 KB

fmt

Formats arguments according to the specified format

The second argument to this filter must be a string literal (as in normal Rust). The two arguments are passed through to format!() by the Rinja code generator, but the order is swapped to support filter composition.

{{ value|fmt("{:?}") }}

As an example, this allows filters to be composed like the following. Which is not possible using the format filter.

{{ value|capitalize|fmt("{:?}") }}

format

Formats arguments according to the specified format.

The first argument to this filter must be a string literal (as in normal Rust).

All arguments are passed through to format!() by the Rinja code generator.

{{ "{:?}"|format(var) }}

indent

Indent newlines with width spaces.

{{ "hello\nfoo\nbar"|indent(4) }}

Output:

hello
    foo
    bar

join

Joins iterable into a string separated by provided argument.

#![allow(unused)]
fn main() {
array = &["foo", "bar", "bazz"]
}

{{ array|join(", ") }}

Output:

foo, bar, bazz

linebreaks

Replaces line breaks in plain text with appropriate HTML.

A single newline becomes an HTML line break <br> and a new line followed by a blank line becomes a paragraph break <p>.

{{ "hello\nworld\n\nfrom\nrinja"|linebreaks }}

Output:

<p>hello<br />world</p><p>from<br />rinja</p>

linebreaksbr

Converts all newlines in a piece of plain text to HTML line breaks.

{{ "hello\nworld\n\nfrom\nrinja"|linebreaks }}

Output:

hello<br />world<br /><br />from<br />rinja

paragraphbreaks

A new line followed by a blank line becomes <p>, but, unlike linebreaks, single new lines are ignored and no <br/> tags are generated.

Consecutive double line breaks will be reduced down to a single paragraph break.

This is useful in contexts where changing single line breaks to line break tags would interfere with other HTML elements, such as lists and nested <div> tags.

{{ "hello\nworld\n\nfrom\n\n\n\nrinja"|paragraphbreaks }}

Output:

<p>hello\nworld</p><p>from</p><p>rinja</p>

lower | lowercase

Converts to lowercase.

{{ "HELLO"|lower }}

Output:

hello

pluralize

Select a singular or plural version of a word, depending on the input value.

If the value of self.count is +1 or -1, then "cat" is returned, otherwise "cats":

cat{{ count|pluralize }}

You can override the default empty singular suffix, e.g. to spell "doggo" for a single dog:

dog{{ count|pluralize("go") }}

If the word cannot be declined by simply adding a suffix, then you can also override singular and the plural, too:

{{ count|pluralize("mouse", "mice") }}

More complex languages that know multiple plurals might be impossible to implement with this filter, though.

ref

Creates a reference to the given argument.

{{ "a"|ref }}
{{ self.x|ref }}

will become:

#![allow(unused)]
fn main() {
&"a"
&self.x
}

safe

Marks a string (or other Display type) as safe. By default all strings are escaped according to the format.

{{ "<p>I'm Safe</p>"|safe }}

Output:

<p>I'm Safe</p>

title

Return a title cased version of the value. Words will start with uppercase letters, all remaining characters are lowercase.

{{ "hello WORLD"|title }}

Output:

Hello World

trim

Strip leading and trailing whitespace.

{{ " hello "|trim }}

Output:

hello

truncate

Limit string length, appends '...' if truncated.

{{ "hello"|truncate(2) }}

Output:

he...

upper | uppercase

Converts to uppercase.

{{ "hello"|upper }}

Output:

HELLO

urlencode

Percent encodes the string. Replaces reserved characters with the % escape character followed by a byte value as two hexadecimal digits.

hello?world

Output:

hello%3Fworld

wordcount

Count the words in that string.

{{ "rinja is sort of cool"|wordcount }}

Output:

5

Optional / feature gated filters

The following filters can be enabled by requesting the respective feature in the Cargo.toml dependencies section, e.g.

[dependencies]
rinja = { version = "0.11.2", features = "serde_json" }

json | tojson

Enabling the serde_json feature will enable the use of the json filter. This will output formatted JSON for any value that implements the required Serialize trait. The generated string does not contain ampersands &, chevrons < >, or apostrophes '.

To use it in a <script> you can combine it with the safe filter. In HTML attributes, you can either use it in quotation marks "{{data|json}}" as is, or in apostrophes with the (optional) safe filter '{{data|json|safe}}'. In HTML texts the output of e.g. <pre>{{data|json|safe}}</pre> is safe, too.

Good: <li data-extra="{{data|json}}">…</li>
Good: <li data-extra='{{data|json|safe}}'>…</li>
Good: <pre>{{data|json|safe}}</pre>
Good: <script>var data = {{data|json|safe}};</script>

Bad:  <li data-extra="{{data|json|safe}}">…</li>
Bad:  <script>var data = {{data|json}};</script>
Bad:  <script>var data = "{{data|json|safe}}";</script>

Ugly: <script>var data = "{{data|json}}";</script>
Ugly: <script>var data = '{{data|json|safe}}';</script>

By default, a compact representation of the data is generated, i.e. no whitespaces are generated between individual values. To generate a readable representation, you can either pass an integer how many spaces to use as indentation, or you can pass a string that gets used as prefix:

Prefix with four spaces:
<textarea>{{data|tojson(4)}}</textarea>

Prefix with two &nbsp; characters:
<p>{{data|tojson("\u{a0}\u{a0}")}}</p>

Custom Filters

To define your own filters, simply have a module named filters in scope of the context deriving a Template impl and define the filters as functions within this module. The functions must have at least one argument and the return type must be ::rinja::Result<T>. Although there are no restrictions on T for a single filter, the final result of a chain of filters must implement Display.

The arguments to the filters are passed as follows. The first argument corresponds to the expression they are applied to. Subsequent arguments, if any, must be given directly when calling the filter. The first argument may or may not be a reference, depending on the context in which the filter is called. To abstract over ownership, consider defining your argument as a trait bound. For example, the trim built-in filter accepts any value implementing Display. Its signature is similar to fn trim(s: impl std::fmt::Display) -> ::rinja::Result<String>.

Note that built-in filters have preference over custom filters, so, in case of name collision, the built-in filter is applied.

Examples

Implementing a filter that replaces all instances of "oo" for "aa".

use rinja::Template;

#[derive(Template)]
#[template(source = "{{ s|myfilter }}", ext = "txt")]
struct MyFilterTemplate<'a> {
    s: &'a str,
}

// Any filter defined in the module `filters` is accessible in your template.
mod filters {
    // This filter does not have extra arguments
    pub fn myfilter<T: std::fmt::Display>(s: T) -> ::rinja::Result<String> {
        let s = s.to_string();
        Ok(s.replace("oo", "aa"))
    }
}

fn main() {
    let t = MyFilterTemplate { s: "foo" };
    assert_eq!(t.render().unwrap(), "faa");
}

Implementing a filter that replaces all instances of "oo" for n times "a".

use rinja::Template;

#[derive(Template)]
#[template(source = "{{ s|myfilter(4) }}", ext = "txt")]
struct MyFilterTemplate<'a> {
    s: &'a str,
}

// Any filter defined in the module `filters` is accessible in your template.
mod filters {
    // This filter requires a `usize` input when called in templates
    pub fn myfilter<T: std::fmt::Display>(s: T, n: usize) -> ::rinja::Result<String> {
        let s = s.to_string();
    	  let mut replace = String::with_capacity(n);
    	  replace.extend((0..n).map(|_| "a"));
        Ok(s.replace("oo", &replace))
    }
}

fn main() {
    let t = MyFilterTemplate { s: "foo" };
    assert_eq!(t.render().unwrap(), "faaaa");
}

HTML-safe types

Rinja will try to avoid escaping types that generate string representations that do not contain "HTML-unsafe characters". HTML-safe characters are characters that can be used in any context in HTML texts and attributes. The "unsafe" characters are: <, >, &, " and '.

In order to know which types do not need to be escaped, rinja has the marker trait rinja::filters::HtmlSafe, and any type that implements that trait won't get automatically escaped in a {{expr}} expression. By default e.g. all primitive integer types are marked as HTML-safe.

You can also mark your custom type MyStruct as HTML-safe using:

#![allow(unused)]
fn main() {
impl rinja::filters::HtmlSafe for MyStruct {}
}

This automatically marks references &MyStruct as HTML-safe, too.

Safe output of custom filters

Say, you have a custom filter |strip that removes all HTML-unsafe characters:

#![allow(unused)]
fn main() {
fn strip(s: impl ToString) -> Result<String, rinja::Error> {
    Ok(s.to_string()
        .chars()
        .filter(|c| !matches!(c, '<' | '>' | '&' | '"' | '\''))
        .collect()
    )
}
}

Then you can also mark the output as safe using rinja::filters::Safe:

#![allow(unused)]
fn main() {
fn strip(s: impl ToString) -> Result<Safe<String>, rinja::Error> {
    Ok(Safe(...))
}
}

There also is rinja::filters::MaybeSafe that can be used to mark some output as safe, if you know that some inputs for our filter will always result in a safe output:

#![allow(unused)]
fn main() {
fn as_sign(i: i32) -> Result<MaybeSafe<&'static str>, rinja::Error> {
    match i.into() {
        i if i < 0 => Ok(MaybeSafe::NeedsEscaping("<0")),
        i if i > 0 => Ok(MaybeSafe::NeedsEscaping(">0")),
        _          => Ok(MaybeSafe::Safe("=0")),
    }
}
}

Integrations

Rocket integration

In your template definitions, replace rinja::Template with rinja_rocket::Template.

Enabling the with-rocket feature appends an implementation of Rocket's Responder trait for each template type. This makes it easy to trivially return a value of that type in a Rocket handler. See the example from the Rinja test suite for more on how to integrate.

In case a run-time error occurs during templating, a 500 Internal Server Error Status value will be returned, so that this can be further handled by your error catcher.

Actix-web integration

In your template definitions, replace rinja::Template with rinja_actix::Template.

Enabling the with-actix-web feature appends an implementation of Actix-web's Responder trait for each template type. This makes it easy to trivially return a value of that type in an Actix-web handler. See the example from the Rinja test suite for more on how to integrate.

Axum integration

In your template definitions, replace rinja::Template with rinja_axum::Template.

Enabling the with-axum feature appends an implementation of Axum's IntoResponse trait for each template type. This makes it easy to trivially return a value of that type in a Axum handler. See the example from the Rinja test suite for more on how to integrate.

In case of a run-time error occurring during templating, the response will be of the same signature, with a status code of 500 Internal Server Error, mime */*, and an empty Body. This preserves the response chain if any custom error handling needs to occur.

Warp integration

In your template definitions, replace rinja::Template with rinja_warp::Template.

Enabling the with-warp feature appends an implementation of Warp's Reply trait for each template type. This makes it simple to return a template from a Warp filter. See the example from the Rinja test suite for more on how to integrate.

Performance

Rendering Performance

When rendering a rinja template, you should prefer the methods

• .render() (to render the content into a new string),
• .render_into() (to render the content into an fmt::Write object, e.g. String) or
• .write_into() (to render the content into an io::Write object, e.g. Vec<u8>)

over .to_string() or format!(). While .to_string() and format!() give you the same result, they generally perform much worse than rinja's own methods, because fmt::Write uses dynamic methods calls instead of monomorphised code. On average, expect .to_string() to be 100% to 200% slower than .render().

Slow Debug Recompilations

If you experience slow compile times when iterating with lots of templates, you can compile Rinja's derive macros with a higher optimization level. This can speed up recompilation times dramatically.

Add the following to Cargo.toml or .cargo/config.toml:

#![allow(unused)]
fn main() {
[profile.dev.package.rinja_derive]
opt-level = 3
}

This may affect clean compile times in debug mode, but incremental compiles will be faster.