Crate minijinja

Expand description

MiniJinja: a powerful template engine for Rust with minimal dependencies

MiniJinja is a simple Jinja2 inspired template engine based on serde. It’s light in features and on dependencies but implements a pretty sizable feature set from Jinja2. It attempts to stay largely compatible in Syntax and behavior:

{% for user in users %}
  <li>{{ user.name }}</li>
{% endfor %}

Why MiniJinja

Rust already has quite a selection of template engines and there are in fact already a handful of engines which are inspired by Jinja2 including Tera and Askama but they are very heavy in terms of dependencies and usage. MiniJinja by its name does not try to become a replacement for these, but it wants to be a good default choice if you need a little bit of templating with minimal dependencies.

MiniJinja tries to juggle these three goals:

aim for a high level of compatibility with Jinja2 templates
provide template rendering and expression evaluation functionality
achieve above functionality with the lest amount of dependencies possible

Template Usage

To use MiniJinja one needs to create an Environment and populate it with templates. Afterwards templates can be loaded and rendered. To pass data one can pass any serde serializable value:

use minijinja::{Environment, context};

let mut env = Environment::new();
env.add_template("hello", "Hello {{ name }}!").unwrap();
let tmpl = env.get_template("hello").unwrap();
println!("{}", tmpl.render(context!(name => "John")).unwrap());

Hello John!

Expression Usage

MiniJinja — like Jinja2 — allows to be used as expression language. This can be useful to express logic in configuration files or similar things. For this purpose the Environment::compile_expression method can be used. It returns an expression object that can then be evaluated, returning the result:

use minijinja::{Environment, context};

let env = Environment::new();
let expr = env.compile_expression("number < 42").unwrap();
let result = expr.eval(context!(number => 23)).unwrap();
assert_eq!(result.is_true(), true);

Debugging

To better understand what’s going on when a template syntax or rendering error happens you should turn on the built-in debug support. Once enabled the errors created by the engine will include helpful error messages with information about where the error happened. For more information see set_debug.

Learn more

syntax: documentation of the template engine syntax.
filters: for how to write custom filters and to see the list of built-in filters.
tests: for how to write custom test functions and to see the list of built-in tests.
functions: for how to write custom functions and to see the list of built-in functions.
value: for information about the runtime value object.
Environment: the main API entry point.
Template: the template object API.

Optional Features

MiniJinja comes with a lot of optional features, some of which are turned on by default. If you plan on using MiniJinja in a library, please consider turning off all default features and to opt-in explicitly into the ones you actually need.

There are some additional features that can be enabled:

source: enables the Source type which helps with dynamic loading of templates.
v_htmlescape: enables the v_htmlescape dependency which implements a faster HTML escaping algorithm.
speedups: enables all speedups (currently v_htmlescape)
unstable_machinery: provides access to the internal machinery of the engine. This is a forever unstable API which mainly exists to aid debugging complex issues.
json: When enabled the tojson filter is added as builtin filter.
urlencode: When enabled the urlencode filter is added as builtin filter.
preserve_order: When enable the internal value implementation uses an indexmap which preserves the original order of maps and structs.

Additionally to cut down on size of the engine some default functionality can be removed:

builtins: if this feature is removed the default filters, tests and functions are not implemented.
sync: this feature makes MiniJinja’s type Send and Sync. If this feature is disabled sending types across threads is often not possible. Thread bounds of things like callbacks however are not changing which means code that uses MiniJinja still needs to be threadsafe.
debug: if this feature is removed some debug functionality of the engine is removed as well. This mainly affects the quality of error reporting.
key_interning: if this feature is removed the automatic string interning in the value type is disabled. The default behavior can cut down on the memory consumption of the value type by interning all string keys used in values.
deserialization: when removed this disables deserialization support for the Value type.