A simple, powerful template engine with minimal dependencies and configurable delimiters.
- Expressions:
{{ user.name }}
- Conditionals:
{% if user.enabled %} ... {% endif %}
- Loops:
{% for user in users %} ... {% endfor %}
- Nested templates:
{% include "nested" %}
- Configurable delimiters:
<? user.name ?>
,(( if user.enabled ))
- Arbitrary user defined filters:
{{ user.name | replace: "\t", " " }}
- Clear and well documented API
- Customizable value formatters:
{{ user.name | escape_html }}
- Render to a
String
or anystd::io::Write
implementor - Render using any
serde
serializable values - Convenient macro for quick rendering:
upon::value!{ name: "John", age: 42 }
- Pretty error messages when displayed using
{:#}
- Format agnostic (does not escape values for HTML by default)
- Minimal dependencies and decent runtime performance
Itβs true there are already a lot of template engines for Rust!
I created upon
because I required a template engine that had runtime
compiled templates, configurable syntax delimiters and minimal dependencies.
I also didnβt need support for arbitrary expressions in the template syntax
but occasionally I needed something more flexible than outputting simple
values (hence filters). Performance was also a concern for me, template
engines like Handlebars and Tera have a lot of features but can be up to
five to seven times slower to render than engines like TinyTemplate.
Basically I wanted something like TinyTemplate with support for configurable delimiters and user defined filter functions. The syntax is inspired by template engines like Liquid and Jinja.
Currently the minimum supported version for upon
is Rust 1.65. Disabling
the filters
feature reduces it to Rust 1.60. The MSRV will only ever
be increased in a breaking release.
First, add the crate to your Cargo manifest.
cargo add upon
Now construct an Engine
. The engine stores the syntax config, filter
functions, formatters, and compiled templates. Generally, you only need to
construct one engine during the lifetime of a program.
let engine = upon::Engine::new();
Next, add_template(..)
is used to compile and store a
template in the engine.
engine.add_template("hello", "Hello {{ user.name }}!")?;
Finally, the template is rendered by fetching it using
template(..)
, calling
render(..)
and rendering to a string.
let result = engine
.template("hello")
.render(upon::value!{ user: { name: "John Smith" }})
.to_string()?;
assert_eq!(result, "Hello John Smith!");
- The
syntax
module documentation outlines the template syntax. - The
filters
module documentation describes filters and how they work. - The
fmt
module documentation contains information on value formatters. - In addition to the examples in the current document, the
examples/
directory in the repository constains some more concrete code examples.
The following crate features are available.
-
filters
(enabled by default) β Enables support for filters in templates (seeEngine::add_filter
). This does not affect value formatters (seeEngine::add_formatter
). Disabling this will improve compile times. -
serde
(enabled by default) β Enables all serde support and pulls in theserde
crate as a dependency. If disabled then you can userender_from(..)
to render templates and construct the context usingValue
βsFrom
impls. -
unicode
(enabled by default) β Enables unicode support and pulls in theunicode-ident
andunicode-width
crates. If disabled then unicode identifiers will no longer be allowed in templates and.chars().count()
will be used in error formatting.
To disable all features or to use a subset you need to set default-features = false
in your Cargo manifest and then enable the features that you would
like. For example to use serde
but disable filters
and
unicode
you would do the following.
[dependencies]
upon = { version = "...", default-features = false, features = ["serde"] }
You can include other templates by name using {% include .. %}
.
let mut engine = upon::Engine::new();
engine.add_template("hello", "Hello {{ user.name }}!")?;
engine.add_template("goodbye", "Goodbye {{ user.name }}!")?;
engine.add_template("nested", "{% include \"hello\" %}\n{% include \"goodbye\" %}")?;
let result = engine.template("nested")
.render(upon::value!{ user: { name: "John Smith" }})
.to_string()?;
assert_eq!(result, "Hello John Smith!\nGoodbye John Smith!");
Instead of rendering to a string it is possible to render the template to
any std::io::Write
implementor using
to_writer(..)
.
use std::io;
let mut engine = upon::Engine::new();
engine.add_template("hello", "Hello {{ user.name }}!")?;
let mut stdout = io::BufWriter::new(io::stdout());
engine
.template("hello")
.render(upon::value!{ user: { name: "John Smith" }})
.to_writer(&mut stdout)?;
// Prints: Hello John Smith!
If the lifetime of the template source is shorter than the engine lifetime
or you donβt need to store the compiled template then you can also use the
compile(..)
function to return the template directly.
let template = engine.compile("Hello {{ user.name }}!")?;
let result = template
.render(&engine, upon::value!{ user: { name: "John Smith" }})
.to_string()?;
assert_eq!(result, "Hello John Smith!");
The compile(..)
function can also be used in
conjunction with a custom template store which can allow for more advanced
use cases. For example: relative template paths or controlling template
access.
let mut store = std::collections::HashMap::<&str, upon::Template>::new();
store.insert("hello", engine.compile("Hello {{ user.name }}!")?);
store.insert("goodbye", engine.compile("Goodbye {{ user.name }}!")?);
store.insert("nested", engine.compile("{% include \"hello\" %}\n{% include \"goodbye\" %}")?);
let result = store.get("nested")
.unwrap()
.render(&engine, upon::value!{ user: { name: "John Smith" }})
.with_template_fn(|name| {
store
.get(name)
.ok_or_else(|| String::from("template not found"))
})
.to_string()?;
assert_eq!(result, "Hello John Smith!\nGoodbye John Smith!");
upon
was benchmarked against several popular template rendering engines in the
Rust ecosystem. Obviously, each of these engines has a completely different
feature set so the benchmark just compares the performance of some of the
features that they share.
- handlebars v4.3.7
- liquid v0.26.4
- minijinja v1.0.5
- tera v1.19.0
- tinytemplate v1.2.1
- upon v0.7.0
Benchmarking was done using criterion on a quiet cloud machine.
Host
- Vultr.com
- 4 CPU
- 8192 MB RAM
- Ubuntu 22.04
- Rust 1.71.0
Licensed under either of
- Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.