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MiniJinja: a powerful template engine for Rust with minimal dependencies

MiniJinja is a powerful but minimal dependency template engine for Rust which is based on the syntax and behavior of the Jinja2 template engine for Python. It’s implemented on top of serde. The goal is to be able to render a large chunk of the Jinja2 template ecosystem from Rust with a minimal engine and to leverage an already existing ecosystem of editor integrations.

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

You can play with MiniJinja online in the browser playground powered by a WASM build of MiniJinja.

Why MiniJinja

MiniJinja by its name wants to be a good default choice if you need a little bit of templating with minimal dependencies. It has the following goals:

  • Well documented, compact API
  • Minimal dependencies, reasonable compile times and decent runtime performance
  • Stay close as possible to Jinja2
  • Support for expression evaluation
  • Support for all serde compatible types
  • Excellent test coverage
  • Support for dynamic runtime objects with methods and dynamic attributes

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. The context! macro can be used to quickly construct a template context:

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!

For super trivial cases where you need to render a string once, you can also use the render! macro which acts a bit like a replacement for the format! macro.

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);

This becomes particularly powerful when dynamic objects are exposed to templates.

Custom Filters

MiniJinja lets you register functions as filter functions (see Filter) with the engine. These can then be invoked directly from the template:

use minijinja::{Environment, context};

let mut env = Environment::new();
env.add_filter("repeat", str::repeat);
env.add_template("hello", "{{ 'Na '|repeat(3) }} {{ name }}!").unwrap();
let tmpl = env.get_template("hello").unwrap();
println!("{}", tmpl.render(context!(name => "Batman")).unwrap());
Na Na Na Batman!

Learn more

  • Environment: the main API entry point. Teaches you how to configure the environment.
  • Template: the template object API. Shows you how templates can be rendered.
  • syntax: provides documentation of the template engine syntax.
  • filters: teaches you how to write custom filters and to see the list of built-in filters.
  • tests: teaches you how to write custom test functions and to see the list of built-in tests.
  • functions: teaches how to write custom functions and to see the list of built-in functions.
  • For auto reloading use the minijinja-autoreload crate.

Additionally there is an list of examples with many different small example programs on GitHub to explore.

Error Handling

MiniJinja tries to give you good errors out of the box. However if you use includes or template inheritance your experience will improve greatly if you ensure to render chained errors. For more information see Error with an example.

Size and Compile Times

MiniJinja attempts to compile fast so it can be used as a sensible template engine choice when compile times matter. Because of this it’s internally modular so unnecessary bits and pieces can be removed. The default set of features tries to strike a balance but in situations where only a subset is needed (eg: build.rs) all default features can be be disabled.

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.

Configurable Features

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

  • Engine Features:

    • builtins: if this feature is removed the default filters, tests and functions are not implemented.
    • macros: when removed the {% macro %} tag is not included.
    • multi_template: when removed the templates related to imports and extends are removed ({% from %}, {% import %}, {% include %}, and {% extends %} as well as {% block %}).
    • adjacent_loop_items: when removed the previtem and nextitem attributes of the loop object no longer exist. Removing this feature can provide faster template execution when a lot of loops are involved.
    • unicode: when added unicode identifiers are supported. Without this features only ASCII identifiers can be used for variable names and attributes.

  • Rust Functionality:

    • debug: if this feature is removed some debug functionality of the engine is removed as well. This mainly affects the quality of error reporting.
    • deserialization: when removed this disables deserialization support for the Value type.

There are some additional features that can be enabled:

  • fuel: enables the fuel feature which makes the engine track fuel consumption which can be used to better protect against expensive templates.
  • source: enables the Source type which helps with dynamic loading of templates.
  • speedups: enables all speedups, in particular it turns on the v_htmlescape dependency for faster HTML escapling.
  • json: When enabled the tojson filter is added as builtin filter as well as the ability to auto escape via AutoEscape::Json.
  • 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.
  • key_interning: if this feature is enabled the automatic string interning in the value type is enabled. This feature used to be turned on by default but has negative performance effects in newer versions of MiniJinja since a lot of the previous uses of key interning are no longer needed. Enabling it however cuts down on memory usage slightly in certain scenarios by interning all string keys used in dynamic map values.
  • custom_syntax: when this feature is enabled, custom delimiters are supported by the parser.

Modules

  • filters
    Filter functions and abstractions.
  • functions
    Global functions and abstractions.
  • syntax
    Documents the syntax for templates.
  • tests
    Test functions and abstractions.
  • testutilstestutils
    Utilities for unit testing.
  • value
    Provides a dynamic value type abstraction.

Macros

  • context
    Creates a template context with keys and values.
  • render
    A macro similar to format! but that uses MiniJinja for rendering.

Structs

  • Environment
    An abstraction that holds the engine configuration.
  • Error
    Represents template errors.
  • Expression
    A handle to a compiled expression.
  • HtmlEscape
    Helper to HTML escape a string.
  • Output
    An abstraction over Write for the rendering.
  • Sourcesource
    Utility for dynamic template loading.
  • State
    Provides access to the current execution state of the engine.
  • Syntaxcustom_syntax
    The delimiter configuration for the environment and the parser.
  • Template
    Represents a handle to a template.

Enums

Functions