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A Haml template engine for Go

Project README

GoHT (Go Haml Templates)

A Haml template engine and file generation tool for Go.

GoHT

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Table of Contents

Features

  • Full Haml language support
  • Templates are compiled to type-safe Go and not parsed at runtime
  • Multiple templates per file
  • Mix Go and templates together in the same file
  • Easy nesting of templates

Quick Start

First create a GoHT file, a file which mixes Go and Haml with a .goht extension:

package main

var siteTitle = "GoHT"

@goht SiteLayout(pageTitle string) {
!!!
%html{lang:"en"}
  %head
    %title= siteTitle
  %body
    %h1= pageTitle
    %p A type-safe HAML template engine for Go.
    = @children
}

@goht HomePage() {
  = @render SiteLayout("Home Page")
    %p This is the home page for GoHT.
}

Your next step will be to process the GoHT file to parse the Haml and generate the Go code using the GoHT CLI tool:

goht generate

Use the generated Go code to render HTML in your application:

package main

import (
	"fmt"
	"log"
	"net/http"
)

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		_ = HomePage().Render(r.Context(), w)
	})

	fmt.Println("Server starting on port 8080...")
	if err := http.ListenAndServe(":8080", nil); err != nil {
		log.Fatal(err)
	}
}

Which would serve the following HTML:

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>GoHT</title>
  </head>
  <body>
    <h1>Home Page</h1>
    <p>A type-safe Haml template engine for Go.</p>
    <p>This is the home page for GoHT.</p>
  </body>
</html>

Supported Haml Syntax & Features

  • Doctypes (!!!)
  • Tags (%tag)
  • Attributes ({name: value}) (more info)
  • Classes and IDs (.class #id) (more info)
  • Object References ([obj]) (more info)
  • Unescaped Text (! !=)
  • Comments (/ -#)
  • Inline Interpolation (#{value})
  • Inlining Code (- code)
  • Rendering Code (= code)
  • Filters (:plain, ...) (more info)
  • Whitespace Removal (%tag> %tag<) (more info)

Unsupported Haml Features

  • Probably something I've missed, please raise an issue if you find something missing.

GoHT CLI

Installation

go install github.com/stackus/goht/cmd/goht@latest

Usage

Use generate to generate Go code from GoHT template files, that are new or newer than the generated Go files, in the current directory and subdirectories:

goht generate

Use the --path flag to specify a path to generate code for:

goht generate --path=./templates

In both examples, the generated code will be placed in the same directory as the template files.

Use the --force to generate code for all GoHT template files, even if they are older than the generated Go files:

goht generate --force

See more options with goht help generate or goht generate -h.

IDE Support

vscode_ide_example.png

LSP

The GoHT CLI has been updated to include an LSP server. See goht help lsp for more information. This will enable development of extensions and plugins for GoHT in various editors and IDEs.

Contributions are welcome. Please see the contributing guide for more information.

Library Installation

When you are using GoHT you will typically be dealing with the generated Go code, and not the GoHT runtime directly. However, if you need to install the GoHT library, you can do so with:

go get github.com/stackus/goht

Using GoHT

To start using GoHT, the first step is to create a GoHT file with one or more Haml templates. If you need guidance, the section The GoHT template has all the information you need.

With your GoHT files written, the next step involves generating Go code from them. The CLI tool handles this generation step. It's a straightforward process that converts your GoHT files and templates into ready to run Go files.

Each generated Go file will include a function corresponding to each of your templates. The names of the functions are not altered at all, if you want them to be exported in Go then you need to use an uppercase letter for the first character of the template name.

When this function is executed, it yields a *goht.Template. This is what you'll use to render your templates in the application.

package main

import (
	"context"
	"os"

	"github.com/stackus/goht/examples/tags"
)

func main() {
	tmpl := tags.RemoveWhitespace()

	err := tmpl.Render(context.Background(), os.Stdout)
	if err != nil {
		panic(err)
	}
}

The above would render the RemoveWhitespace example from the examples directory in this repository, and would output the following:

<p>This text has no whitespace between it and the parent tag.</p>
<p>
There is whitespace between this text and the parent tag.<p>This text has no whitespace between it and the parent tag.
There is also no whitespace between this tag and the sibling text above it.
Finally, the tag has no whitespace between it and the outer tag.</p></p>

The second parameter passed into the Render method can be anything that implements the io.Writer interface, such as a file or a buffer, or the http.ResponseWriter that you get from an HTTP handler.

Using GoHT with HTTP handlers

Using the GoHT templates is made very easy.

package main

import (
	"fmt"
	"log"
	"net/http"

	"github.com/stackus/goht/examples/hello"
)

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		_ = hello.World().Render(r.Context(), w)
	})

	fmt.Println("Server starting on port 8080...")
	if err := http.ListenAndServe(":8080", nil); err != nil {
		log.Fatal(err)
	}
}

There are a number of examples showing various Haml and GoHT features in the examples directory.

A big nod to Templ

The way that you use GoHT is very similar to how you would use Templ. This is no accident as I am a big fan of the work being done with that engine.

After getting the Haml properly lexed, and parsed, I did not want to reinvent the wheel and come up with a whole new rendering API. The API that Templ presents is nice and easy to use, so I decided to replicate it in GoHT.

The GoHT template

GoHT templates are files with the extension .goht that when processed will produce a matching Go file with the extension .goht.go.

In these files you are free to write any Go code that you wish, and then drop into Haml mode using the @goht directive.

The following starts the creation of a SiteLayout template:

@goht SiteLayout() {

GoHT templates are closed like Go functions, with a closing brace }. So a complete but empty example is this:

@goht SiteLayout() {
}

Inside the template you can use any Haml features, such as tags, attributes, classes, IDs, text, comments, interpolation, code inlining, code rendering, and filters.

Haml Syntax

The Haml syntax is documented at the Haml website. Please see that site or the Haml Reference for more information.

GoHT has implemented the Haml syntax very closely. So, if you are already familiar with Haml then you should be able to jump right in. There are some minor differences that I will document in the next section.

GoHT and Haml differences

Important differences are:

Go package and imports

You can provide a package name at the top of your GoHT template file. If you do not provide one then main will be used.

You may also import any packages that you need to use in your template. The imports you use and the ones brought in by GoHT will be combined and deduplicated.

Multiple templates per file

You can declare as many templates in a file as you wish. Each template must have a unique name in the module they will be output into.

@goht SiteLayout() {
}

@goht HomePage() {
}

The templates are converted into Go functions, so they must be valid Go function names. This also means that you can declare them with parameters and can use those parameters in the template.

@goht SiteLayout(title string) {
!!!
%html{lang:"en"}
  %head
    %title= title
  %body
    -# ... the rest of the template
}

Doctypes

Only the HTML 5 doctype is supported, and is written using !!!.

@goht SiteLayout() {
!!!
}

Note about indenting. GoHT follows the same rules as Haml for indenting. The first line of the template must be at the same level as the @goht directive. After that, you may use spaces or tabs to indent the content of the template. However, you must be consistent with the use of spaces or tabs. Mixing them will cause an error. As will indenting more than one level at a time.

Inlined code

You won't be using Ruby here, you'll be using Go. In most situations where we would need to include opening and closing braces in Go, we can omit them in GoHT. This makes it a lot closer to the Ruby-based Haml, and makes the templates easier to read. Go will still require we have a full statement, no shorthands for boolean conditionals. So instead of this with Ruby:

- if user
  %strong The user exists

You would write this with Go:

- if user != nil
  %strong The user exists

There is minimal processing performed on the Go code you put into the templates, so it needs to be valid Go code sans braces.

You may continue to use the braces if you wish. Existing code with braces will continue to work without modifications.

Rendering code

Like in Haml, you can output variables and the results of expressions. The = script syntax and text interpolation #{} are supported.

%strong= user.Name
%strong The user's name is #{user.Name}

The catch is what is being outputted will need to be a string in all cases. So instead of writing this to output an integer value:

%strong= user.Age

You would need to write this:

%strong= fmt.Sprintf("%d", user.Age)

Which to be honest can be a bit long to write, so a shortcut is provided:

%strong=%d user.Age

The interpolation also supports the shortcut:

%strong #{user.Name} is #{%d user.Age} years old.

When formatting a value into a string fmt.Sprintf is used under the hood, so you can use any of the formatting options that it supports.

Attributes

Only the Ruby 1.9 style of attributes is supported. This syntax is closest to the Go syntax, and is the most readable. Between the attribute name, operator, and value you can include or leave out as much whitespace as you like.

%a{href: "https://github.com/stackus/goht", target: "_blank"} GoHT

You can supply a value to an attribute using the text interpolation syntax.

%a{href:#{url}} GoHT

Attributes can be written over multiple lines, and the closing brace can be on a new line.

%a{
  href: "...",
  target: "_blank",
} GoHT

Attributes which you want to render conditionally use the ? operator instead of the : operator. For conditional attributes the attribute value is required to be an interpolated value which will be used as the condition in a Go if statement.

%button{
  disabled ? #{disabled},
} Click me

Note: The final comma is not required on the last attribute when they are spread across multiple lines like it would be in Go. Including it is fine and will not cause any issues.

Certain characters in the attribute name will require that the name be escaped.

%button{
  "@click": "onClick",
  ":disabled": "disabled",
} Click me

Keep in mind that attribute names cannot be replaced with an interpolated string; only the value can.

To support dynamic lists of attributes, you can use the @attributes directive. This directive takes a list of arguments which comes in two forms:

  • map[string]string
    • The key is the attribute name, the value is the attribute value.
    • The attribute will be rendered if the value is not empty.
  • map[string]bool
    • The key is the attribute name, the value is the condition to render the attribute.
%button{
  "@click": "onClick",
  ":disabled": "disabled",
  @attributes: #{myAttrs},
} Click me

Classes

GoHT supports the . operator for classes and also will accept the class attribute such as class:"foo bar". However, if the class attribute is given an interpolated value, it will need to be a comma separated list of values. These values can be the following types:

  • string
    • myClass variable or "foo bar" string literal
  • []string
    • Each item will be added to the class list if it is not blank.
  • map[string]bool
    • The key is the class name, the value is the condition to include the class.

Examples:

%button.foo.bar.baz Click me
%button.fizz{class:"foo bar baz"} Click me
%button.foo{class:#{myStrClasses, myBoolClasses}} Click me

All sources of classes will be combined and deduplicated into a single class attribute.

Object References

Haml supports using a Ruby object to supply the id and class for a tag using the [] object reference syntax. This is supported but is rather limited in GoHT. The type that you use within the brackets will be expected to implement at least one or both of the following interfaces:

type ObjectIDer interface {
  ObjectID() string
}

type ObjectClasser interface {
  ObjectClass() string
}

The result of these methods will be used to populate the id and class attributes in a similar way to how Haml would apply the Ruby object references.

Filters

Only the following Haml filters are supported:

  • :plain
  • :escaped
  • :preserve
  • :javascript
  • :css

Template nesting

The biggest departure from Haml is how templates can be combined. When working Haml you could use = render :partial_name or = haml :partial_name to render a partial. The render and haml functions are not available in GoHT, instead you can use the @render directive.

@goht HomePage() {
= @render SiteLayout()
}

The above would render the SiteLayout template, and you would call it with any parameters that it needs. You can also call it and provide it with a block of content to render where it chooses.

@goht HomePage() {
= @render SiteLayout()
  %p This is the home page for GoHT.
}

Any content nested under the @render directive will be passed into the template that it can render where it wants using the @children directive.

@goht SiteLayout() {
!!!
%html{lang:"en"}
  %head
    %title GoHT
  %body
    %h1 GoHT
    %p A HAML-like template engine for Go.
    = @children
}

Contributing

Contributions are welcome. Please see the contributing guide for more information.

License

MIT

Open Source Agenda is not affiliated with "Stackus Hamlet" Project. README Source: stackus/goht
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Last Commit
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Repository
stackus/goht
License
MIT
Homepage
https://goht.dev
Tags
Golang Haml HTML Templates Type Safe Language Server Language Server Protocol Lsp

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