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# HAML

[HAML](https://haml.info/) is the [Ruby on Rails](https://rubyonrails.org/) template language that GitLab uses.

## GitLab UI form builder

[GitLab UI](https://gitlab-org.gitlab.io/gitlab-ui/) is a Vue component library that conforms
to the [Pajamas design system](https://design.gitlab.com/). Most of these components
rely on JavaScript and therefore can only be used in Vue.

However, some of the simpler components (checkboxes, radio buttons, form inputs) can be
used in HAML by applying the correct CSS classes to the elements. A custom
[Ruby on Rails form builder](https://gitlab.com/gitlab-org/gitlab/-/blob/7c108df101e86d8a27d69df2b5b1ff1fc24133c5/lib/gitlab/form_builders/gitlab_ui_form_builder.rb) exists to help use GitLab UI components in HAML.

### Use the GitLab UI form builder

To use the GitLab UI form builder:

1. Change `form_for` to `gitlab_ui_form_for`.
1. Change `f.check_box` to `f.gitlab_ui_checkbox_component`.
1. Remove `f.label` and instead pass the label as the second argument in `f.gitlab_ui_checkbox_component`.

For example:

- Before:

  ```haml
  = form_for @group do |f|
    .form-group.gl-mb-3
      .gl-form-checkbox.custom-control.custom-checkbox
        = f.check_box :prevent_sharing_groups_outside_hierarchy, disabled: !can_change_prevent_sharing_groups_outside_hierarchy?(@group), class: 'custom-control-input'
        = f.label :prevent_sharing_groups_outside_hierarchy, class: 'custom-control-label' do
          %span
            = s_('GroupSettings|Prevent members from sending invitations to groups outside of %{group} and its subgroups.').html_safe % { group: link_to_group(@group) }
          %p.help-text= prevent_sharing_groups_outside_hierarchy_help_text(@group)
  ```

- After:

  ```haml
  = gitlab_ui_form_for @group do |f|
    .form-group.gl-mb-3
      = f.gitlab_ui_checkbox_component :prevent_sharing_groups_outside_hierarchy,
          s_('GroupSettings|Prevent members from sending invitations to groups outside of %{group} and its subgroups.').html_safe % { group: link_to_group(@group) },
          help_text: prevent_sharing_groups_outside_hierarchy_help_text(@group),
          checkbox_options: { disabled: !can_change_prevent_sharing_groups_outside_hierarchy?(@group) }
  ```

### Available components

When using the GitLab UI form builder, the following components are available for use in HAML.

NOTE:
Currently only the listed components are available but more components are planned.

#### gitlab_ui_checkbox_component

[GitLab UI Docs](https://gitlab-org.gitlab.io/gitlab-ui/?path=/story/base-form-form-checkbox--default)

| Argument | Description | Type | Required (default value) |
|---|---|---|---|
| `method` | Attribute on the object passed to `gitlab_ui_form_for`. | `Symbol` | `true` |
| `label` | Checkbox label. | `String` | `true` |
| `help_text` | Help text displayed below the checkbox. | `String` | `false` (`nil`) |
| `checkbox_options` | Options that are passed to [Rails `check_box` method](https://api.rubyonrails.org/classes/ActionView/Helpers/FormBuilder.html#method-i-check_box). | `Hash` | `false` (`{}`) |
| `checked_value` | Value when checkbox is checked. | `String` | `false` (`'1'`) |
| `unchecked_value` | Value when checkbox is unchecked. | `String` | `false` (`'0'`) |
| `label_options` | Options that are passed to [Rails `label` method](https://api.rubyonrails.org/classes/ActionView/Helpers/FormBuilder.html#method-i-label). | `Hash` | `false` (`{}`) |

#### gitlab_ui_radio_component

[GitLab UI Docs](https://gitlab-org.gitlab.io/gitlab-ui/?path=/story/base-form-form-radio--default)

| Argument | Description | Type | Required (default value) |
|---|---|---|---|
| `method` | Attribute on the object passed to `gitlab_ui_form_for`. | `Symbol` | `true` |
| `value` | The value of the radio tag. | `Symbol` | `true` |
| `label` | Radio label. | `String` | `true` |
| `help_text` | Help text displayed below the radio button. | `String` | `false` (`nil`) |
| `radio_options` | Options that are passed to [Rails `radio_button` method](https://api.rubyonrails.org/classes/ActionView/Helpers/FormBuilder.html#method-i-radio_button). | `Hash` | `false` (`{}`) |
| `label_options` | Options that are passed to [Rails `label` method](https://api.rubyonrails.org/classes/ActionView/Helpers/FormBuilder.html#method-i-label). | `Hash` | `false` (`{}`) |
