goht

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README

GoHT (Go HTML Templates)

A Haml, Slim, and EGO template engine and file generation tool for Go.

GoHT

Go Report Card Coverage Status

Table of Contents

Features

  • Full Haml language support
  • Full Slim language support
  • EGO support (EJS or ERB like syntax)
  • 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 (and Slim!) with a .goht extension:

package main

var siteTitle = "GoHT"

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

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

@ego ListItemFragment(item Item) {
  <li>
    <a href="<%= item.URL %>">
      <%= item.Name %>
    </a>
  </li>
}

Your next step will be to process the GoHT file to parse the GoHT code 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 (/ -#)
  • Self-closing Tags (%tag/)]
  • Inline Interpolation (#{value})
  • Inlining Code (- code)
  • Rendering Code (= code)
  • Filters (:plain, ...) (more info)
  • Long Statement wrapping (\), (,)
  • Whitespace Removal (%tag>, %tag<) (more info)
Unsupported Haml Features
  • Probably something I've missed, please raise an issue if you find something missing.

Supported Slim Syntax & Features

  • Doctypes (doctype)
  • Tags (tag)
  • Attributes ({name: value}) (more info)
  • Classes and IDs (.class, #id) (more info)
  • Inline Tags (tag: othertag)
  • Unescaped Text (|)
  • Comments (/, /!)
  • Self-closing Tags (tag/)
  • Inline Interpolation (#{value})
  • Inlining Code (- code)
  • Rendering Code (= code, == code)
  • Filters (:javascript, :css) (more info)
  • Long Statement wrapping (\), (,)
  • Whitespace Addition (tag< tag>) (more info)
Unsupported Slim Features
  • Probably something I've missed, please raise an issue if you find something missing.
Supported EGO tags

The basic EGO syntax is to start tags and with <% and end with %>.

The opening tags that are supported are:

  • <% - Start of a Go code block
    • Examples: <% for k, v := range list { %>, <% foo := "bar" %>, <% if foo == "bar" { %>
  • <%- - Start of a Go code block with whitespace stripping
    • Examples: <%- for k, v := range list { %>, <%- foo := "bar" %>, <%- if foo == "bar" { %>
  • <%= - Start of a Go output block; supports the formatting directives like %d, %v, etc.
    • Examples: <%= unsafeHTML %>, <%= %t someBool %>, <%= props.Value %>
  • <%! - Start of a Go unescaped output block; supports the formatting directives like %d, %v, etc.
    • Examples: <%! safeHTML %>, <%! %t someBool %>, <%! props.Value %>
  • <%@ - Start of a command block; Either @render or @children
    • Examples: <%@ render ExampleChild(props ChildProps) { %>, <%@ children %>
  • <%# - Start of a comment; the content will be ignored
    • Examples: <%# This is a comment %>

The closing tags that are supported are:

  • %> - Normal closing tag
    • Examples: <% foo := "bar" %>, <%= foo %>
  • -%> - Closing tag with whitespace stripping
    • Examples: <% foo := "bar" -%>, <%= foo -%>
  • $%> - Closing tag with newline stripping (one newline)
    • Examples: <% foo := "bar" $%>, <%= foo $%>

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

Note: The IDE extensions are being worked on to add the new Slim syntax highlighting.

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 straightforward.

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)
  }
}

More Examples!

There are a number of examples showing various template 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 @haml directive.

Note: The original @goht directive is still supported for HAML templating, but it is deprecated and will be removed in a future version.

The following starts the creation of a SiteLayout template:

@haml SiteLayout() {

or

@slim SiteLayout() {

or

@ego SiteLayout() {

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

@haml SiteLayout() {
}

or

@slim SiteLayout() {
}

or

@ego SiteLayout() {
}

Inside the templates you must indent the contents of the template code at least once. This is a requirement of GoHT.

GoHT Syntax

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

GoHT has implemented nearly all Haml and Slim syntax that are whitespace indented syntaxes. It also supports the EGO syntax which is a syntax more like normal HTML. So, if you are already familiar with Haml, Slim, or are familiar with either EJS (Embedded JavaScript) or ERB (Embedded Ruby) then you should be able to jump right in. There are some minor differences that I will document in the next section.

GoHT template differences

Important differences are:

  • Go package and imports: You can declare a package and imports for your templates.
  • Multiple templates per file: You can declare as many templates in a file as you wish.
  • Doctypes: Haml and Slim only. Limited doctype support.
  • Indents: GoHT follows the rules of GoFMT for indents.
  • Inlined code: You won't be using Ruby here, you'll be using Go.
  • Rendering code: The catch is what is being outputted will need to be a string in all cases.
  • Attributes: Haml and Slim only. Only the Ruby 1.9 ({...}) style of attributes is supported.
  • Classes: Haml and Slim only. Multiple sources of classes are supported.
  • Object References: Haml Only: Limited support for object references.
  • Filters: Haml and Slim only. Partial list of supported filters.
  • Template nesting: Templates can be nested, and content can be passed into them.

In the above list, EGO doesn't have many of the limitations of the other two languages. This is because anything outside the EGO tags can be or contain whatever you want.

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. You may also mix all three template types in the same file.

@slim SiteLayout() {
}

@haml HomePage() {
}

@ego ListItem(item Item) {
}

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.

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

The same applies to Slim templates:

@slim SiteLayout(title string) {
  doctype html
  html(lang="en")
    head
      title= title
    body
      / ... the rest of the template
}

And to the EGO templates:

@ego SiteLayout(title string) {
  <html lang="en">
    <head>
      <title><%= title %></title>
    </head>
    <body>
      <!-- ... the rest of the template -->
    </body>
  </html>
}
Doctypes

Only the HTML 5 doctype is supported in the Haml and Slim templates, and is written using !!! or doctype.

@haml SiteLayout() {
  !!!
}

@slim SiteLayout() {
  doctype
}
Indents

GoHT follows the rules of GoFMT for indents, meaning that you should use tabs for indentation. For the Haml and Slim templates, you must use tabs throughout the entire template. For the EGO templates, you may use spaces after the initial tab indent required for each line.

Note: Two spaces are being used in this README for display only. Keep that in mind if you copy and paste the examples from this document.

You must also indent the content of the Haml and Slim templates, and the closing brace should be at the same level as the template directive.

@haml SiteLayout() {
  %html
    %head
      %title GoHT
    %body
      %h1 GoHT
}

Slim:

@slim SiteLayout() {
  doctype
  html
    head
      title GoHT
    body
      h1 GoHT
}

EGO:

@ego SiteLayout() {
  <html>
    <head>
      <title>GoHT</title>
    </head>
    <body>
      <h1>GoHT</h1>
    </body>
  </html>
}
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 that 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 (Go needs the != nil check):

  - 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 in the Haml and Slim templates at the ends of your lines if you wish. Existing code with braces will continue to work without modifications.

Long statements can be split across multiple lines by ending each line with either a backslash \ or a comma ,. The backslashes will be stripped, but the commas will be kept.

  - if user != nil && user.Name != ""\
    && user.Age > 0
    %strong The user is not empty

You can also spread statements across multiple lines in the EGO templates. Take care that the code is valid Go code because the entire statement, with newlines and whitespace, is all captured.

@ego SiteLayout() {
  <% if user != nil && 
    user.Name != "" { %>
    <strong>The user is not empty</strong>
  <% } %>
}
Rendering code

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

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

Slim:

  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 syntax 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

Haml and Slim Only

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

Haml and Slim Only

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 Only

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.

Inlined Tags

Slim Only

GoHT supports inlining tags to keep templates as compact as possible.

  ul
    li: a.First Fist Item
    li: a.Second Second Item
    li: a.Third Third Item
Filters

Only the following Haml filters are supported:

  • :plain (Haml Only)
  • :escaped (Haml Only)
  • :preserve (Haml Only)
  • :javascript
  • :css
Whitespace Removal

Haml Only

GoHT supports the removal of whitespace between tags. This is done by adding a > or < to the end of the tag.

  • > will remove all whitespace between the tag and its parent or siblings.
  • < will remove all whitespace between the tag and its first and last child.

Both can be used together to remove whitespace both inside and outside a tag; the order they're in does not matter.

Whitespace Addition

Slim Only

GoHT supports the addition of whitespace between tags. This is done by adding a < or > to the end of the tag.

  • < will add whitespace before the tag
  • > will add whitespace after the tag
Template nesting

The biggest departure from Haml and Slim 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.

Haml:

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

Slim:

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

EGO:

@ego HomePage() {
  <%@render SiteLayout() %>
}

The above examples 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 the rendered template chooses.

*Haml:

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

Slim:

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

EGO:

@ego HomePage() {
  <%@render SiteLayout() { %>
    <p>This is the home page for GoHT.</p>
  <% } %>
}

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

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

Named slots are a feature that allows you to define places in your templates that you want to populate with any template content. This allows you to create more complex templates that can be reused in different contexts.

Haml:

@haml HamlSlots() {
  .basic
    =@slot basic
  .with-default-content
    =@slot defaults
      %span Displayed when nothing is passed in for "defaults"
}

Slim:

@slim SlimSlots() {
  .basic
    =@slot basic
  .with-default-content
    =@slot defaults
      span Displayed when nothing is passed in for "defaults"
}

EGO:

@ego EgoSlots() {
  <div>
    <%@slot basic %>
  </div>
  <div>
    <%@slot defaults { %>
      <span>Displayed when nothing is passed in for "defaults"</span>
    <% } %>
  </div>
}

In the above examples, the slot for "basic" will only be rendered if content is passed in for it. The slot for "defaults" will fall back to the default content if no content is passed in for it.

Using slots in your program

Making use of slots in your program is a simple process:

err := SomeTemplate().Render(ctx, w, 
  OtherTemplate().Slot("basic"),
)

Start by passing in one or more templates into the optional third parameter of the Render method. Then instead of calling Render on the slotted template, call Slot with the name of the slot you want it to fill.

The slotted templates can be any template, and any template can be used as slotted content, including templates that have their own slots.

err := Layout().Render(ctx, w,
  Sidebar().Slot("sidebar"),
  Header(headerProps).Slot("header"),
  UserDetailsPage(userProps).Slot("main",
    LastActionResults(resultsProps).Slot("notifications"),
  ),
  Footer().Slot("footer"),
)

Templates can use slots, @slot <name> and the internally rendered templates, @render SomeTemplate() and @children, to create templates with incredible levels of reuse and composition.

Contributing

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

License

MIT

Documentation

Index

Constants

View Source 
const (
	NukeAfter  = "~☢<"
	NukeBefore = ">☢~"
)

little nuke alligators that eat whitespace; silly but important

Variables

This section is empty.

Functions

func BuildAttributeList 

func BuildAttributeList(attributes ...any) (string, error)

func BuildClassList 

func BuildClassList(classes ...any) (string, error)

func CaptureErrors 

func CaptureErrors(s string, errs ...error) (string, error)

func EscapeString 

func EscapeString(s string) string

func FormatString 

func FormatString(format string, value any) string

func If added in v0.4.3 

func If(condition bool, trueValue, falseValue string) string

If returns the trueValue if the condition is true, otherwise falseValue.

func ObjectClass 

func ObjectClass(obj any, prefix ...string) string

func ObjectID 

func ObjectID(obj any, prefix ...string) string

func PushChildren 

func PushChildren(ctx context.Context, children Template) context.Context

func ReleaseBuffer 

func ReleaseBuffer(buf Buffer)

func Version 

func Version() string

Types

type Buffer added in v0.4.2 

type Buffer struct {
	*bytes.Buffer
}

func GetBuffer 

func GetBuffer() Buffer

func (*Buffer) Bytes added in v0.4.2 

func (b *Buffer) Bytes() []byte

type ObjectClasser 

type ObjectClasser interface {
	ObjectClass() string
}

type ObjectIDer 

type ObjectIDer interface {
	ObjectID() string
}

type SlottedTemplate added in v0.8.0 

type SlottedTemplate interface {
	Template
	SlotName() string
	SlottedTemplates() []SlottedTemplate
}

func GetSlottedTemplate added in v0.8.0 

func GetSlottedTemplate(slottedTemplates []SlottedTemplate, slotName string) SlottedTemplate

type Template 

type Template interface {
	Render(ctx context.Context, w io.Writer, slottedTemplates ...SlottedTemplate) error
	Slot(slotName string, slottedTemplates ...SlottedTemplate) SlottedTemplate
}

Template is a template that can be rendered into a writer.

func PopChildren 

func PopChildren(ctx context.Context) (context.Context, Template)

type TemplateFunc 

type TemplateFunc func(ctx context.Context, w io.Writer, slottedTemplates ...SlottedTemplate) error

func (TemplateFunc) Render 

func (f TemplateFunc) Render(ctx context.Context, w io.Writer, slottedTemplates ...SlottedTemplate) error

func (TemplateFunc) Slot added in v0.8.0 

func (f TemplateFunc) Slot(slotName string, slottedTemplates ...SlottedTemplate) SlottedTemplate

Source Files

View all Source files

Directories

Path Synopsis
cmd
goht
goht/cmd
examples
attributes
commands
comments
doctype
filters
formatting
go
hello
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internal
logging
protocol
proxy

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