liquid README

The project's README from github.com/Shopify/liquid. As one markdown file: README.md.

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Liquid template engine

Introduction

Liquid is a template engine which was written with very specific requirements:

Why you should use Liquid

What does it look like?

<ul id="products">
  {% for product in products %}
    <li>
      <h2>{{ product.name }}</h2>
      Only {{ product.price | price }}

      {{ product.description | prettyprint | paragraph }}
    </li>
  {% endfor %}
</ul>

How to use Liquid

Install Liquid by adding gem 'liquid' to your gemfile.

Liquid supports a very simple API based around the Liquid::Template class. For standard use you can just pass it the content of a file and call render with a parameters hash.

@template = Liquid::Template.parse("hi {{name}}") # Parses and compiles the template
@template.render('name' => 'tobi')                # => "hi tobi"

Concept of Environments

In Liquid, a "Environment" is a scoped environment that encapsulates custom tags, filters, and other configurations. This allows you to define and isolate different sets of functionality for different contexts, avoiding global overrides that can lead to conflicts and unexpected behavior.

By using environments, you can:

  1. Encapsulate Logic: Keep the logic for different parts of your application separate.
  2. Avoid Conflicts: Prevent custom tags and filters from clashing with each other.
  3. Improve Maintainability: Make it easier to manage and understand the scope of customizations.
  4. Enhance Security: Limit the availability of certain tags and filters to specific contexts.

We encourage the use of Environments over globally overriding things because it promotes better software design principles such as modularity, encapsulation, and separation of concerns.

Here's an example of how you can define and use Environments in Liquid:

user_environment = Liquid::Environment.build do |environment|
  environment.register_tag("renderobj", RenderObjTag)
end

Liquid::Template.parse(<<~LIQUID, environment: user_environment)
  {% renderobj src: "path/to/model.obj" %}
LIQUID

In this example, RenderObjTag is a custom tag that is only available within the user_environment.

Similarly, you can define another environment for a different context, such as email templates:

email_environment = Liquid::Environment.build do |environment|
  environment.register_tag("unsubscribe_footer", UnsubscribeFooter)
end

Liquid::Template.parse(<<~LIQUID, environment: email_environment)
  {% unsubscribe_footer %}
LIQUID

By using Environments, you ensure that custom tags and filters are only available in the contexts where they are needed, making your Liquid templates more robust and easier to manage. For smaller projects, a global environment is available via Liquid::Environment.default.

Error Modes

Setting the error mode of Liquid lets you specify how strictly you want your templates to be interpreted. Normally the parser is very lax and will accept almost anything without error. Unfortunately this can make it very hard to debug and can lead to unexpected behaviour.

Liquid also comes with different parsers that can be used when editing templates to give better error messages when templates are invalid. You can enable this new parser like this:

Liquid::Environment.default.error_mode = :strict2 # Raises a SyntaxError when invalid syntax is used in all tags
Liquid::Environment.default.error_mode = :strict  # Raises a SyntaxError when invalid syntax is used in some tags
Liquid::Environment.default.error_mode = :warn    # Adds strict errors to template.errors but continues as normal
Liquid::Environment.default.error_mode = :lax     # The default mode, accepts almost anything.

If you want to set the error mode only on specific templates you can pass :error_mode as an option to parse:

Liquid::Template.parse(source, error_mode: :strict)

This is useful for doing things like enabling strict mode only in the theme editor.

It is recommended that you enable :strict or :warn mode on new apps to stop invalid templates from being created. It is also recommended that you use it in the template editors of existing apps to give editors better error messages.

Undefined variables and filters

By default, the renderer doesn't raise or in any other way notify you if some variables or filters are missing, i.e. not passed to the render method. You can improve this situation by passing strict_variables: true and/or strict_filters: true options to the render method. When one of these options is set to true, all errors about undefined variables and undefined filters will be stored in errors array of a Liquid::Template instance. Here are some examples:

template = Liquid::Template.parse("{{x}} {{y}} {{z.a}} {{z.b}}")
template.render({ 'x' => 1, 'z' => { 'a' => 2 } }, { strict_variables: true })
#=> '1  2 ' # when a variable is undefined, it's rendered as nil
template.errors
#=> [#<Liquid::UndefinedVariable: Liquid error: undefined variable y>, #<Liquid::UndefinedVariable: Liquid error: undefined variable b>]

template = Liquid::Template.parse("{{x | filter1 | upcase}}")
template.render({ 'x' => 'foo' }, { strict_filters: true })
#=> '' # when at least one filter in the filter chain is undefined, a whole expression is rendered as nil
template.errors
#=> [#<Liquid::UndefinedFilter: Liquid error: undefined filter filter1>]

If you want to raise on a first exception instead of pushing all of them in errors, you can use render! method:

template = Liquid::Template.parse("{{x}} {{y}}")
template.render!({ 'x' => 1}, { strict_variables: true })
#=> Liquid::UndefinedVariable: Liquid error: undefined variable y

Usage tracking

To help track usages of a feature or code path in production, we have released opt-in usage tracking. To enable this, we provide an empty Liquid:: Usage.increment method which you can customize to your needs. The feature is well suited to https://github.com/Shopify/statsd-instrument. However, the choice of implementation is up to you.

Once you have enabled usage tracking, we recommend reporting any events through Github Issues that your system may be logging. It is highly likely this event has been added to consider deprecating or improving code specific to this event, so please raise any concerns.

liquid (Shopify/liquid)

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Liquid
Что это такое?Liquid — это движок шаблонов от Shopify, который позволяет встраивать динамическое содержимое в HTML, письма или другой текст и при этом оставаться безопасным для ненадёжных шаблонов, написанных пользователями.
Это фреймворк или библиотека?Это библиотека (гем) для Ruby, которую вы встраиваете в своё приложение. Её основа — класс Liquid::Template, с помощью которого вы компилируете шаблоны и выполняете их рендеринг.
Как добавить это в проект?Добавьте gem 'liquid' в свой Gemfile, затем передайте содержимое шаблона в Liquid::Template и вызовите render с хешем переменных.
Что нужно установить перед использованием?Достаточно Ruby и гема Liquid — у него нет перечисленных внешних зависимостей.
Он по умолчанию строго проверяет мои шаблоны?Нет, парсер по умолчанию работает в режиме lax и принимает почти всё без ошибок, из-за чего отлаживать код может быть трудно; для более надёжной проверки нужно включить режим ошибок :strict или :warn.
Зачем выбирать Liquid, а не просто использовать eval для кода шаблонов?Liquid никогда не выполняет eval для кода шаблонов, поэтому он рассчитан на то, чтобы конечные пользователи могли редактировать шаблоны и не получали возможности запускать произвольный код на вашем сервере.
Что такое Environment в Liquid?Environment — это изолированный контейнер для пользовательских тегов, фильтров и настроек. Он позволяет разделять функциональность между контекстами (например, пользовательскими темами и шаблонами писем) вместо использования глобальных переопределений.
Можно ли сделать так, чтобы Liquid выдавал ошибку при отсутствии переменных, а не молча их пропускал?Да, передайте strictvariables: true и/или strictfilters: true в render или используйте render!, чтобы получить исключение при первой неопределённой переменной или ошибке фильтра.
Для чего нужна функция отслеживания использования?Это включаемый по желанию хук Liquid::Usage.increment, который можно настроить для журналирования того, как используются определённые функции или участки кода в продакшене. Это полезно для отслеживания устаревающих возможностей.
What are similar projects?handlebars.js, mermaid, markdown-it, stylus, devise, user.js, bootstrap-sass, reactionview
Which topics is it in?markup, ruby, template, security, library, web, mit, open-source
Creator
Shopify
Size
6.4 MB
Stars
11.9K
Updated
CommitSep 17Releasev5.13.0Jun 29
Age
18y
Commits · 90 Days