Add option for controlling when form fields should be nested under th…

…eir parent (#1711)

.changeset/silly-flowers-smell.md

@@ -0,0 +1,5 @@
+---
+'@primer/view-components': patch
+---
+
+Add option for controlling when form fields should be nested under their parent

lib/primer/forms/builder.rb

@@ -33,6 +33,8 @@ class Builder < ActionView::Helpers::FormBuilder
 
       UTILITY_KEYS = Primer::Classify::Utilities::UTILITIES.keys.freeze
 
+      alias primer_fields_for fields_for
+
       def label(method, text = nil, **options, &block)
         super(method, text, classify(options).merge(generate_error_markup: false), &block)
       end

lib/primer/forms/dsl/form_reference_input.rb

@@ -5,11 +5,34 @@ module Forms
     module Dsl
       # :nodoc:
       class FormReferenceInput < Input
-        attr_reader :ref_block, :fields_for_args, :fields_for_kwargs
+        attr_reader :ref_block, :fields_for_args, :fields_for_kwargs, :nested
+        alias nested? nested
 
-        def initialize(*fields_for_args, builder:, form:, **fields_for_kwargs, &block)
+        # Pass `nested: false` to prevent the referenced form fields from being treated as nested
+        # under the parent form's model. For example, consider these models:
+
+        # class User < ActiveRecord::Base
+        #   has_many :addresses
+        # end
+
+        # class Address < ActiveRecord::Base
+        #   belongs_to :user
+        # end
+
+        # A sign-up form might include fields from `User` as well as `Address`. Since addresses are
+        # associated with users, it's perfectly natural to accept the address fields as nested
+        # attributes. Rails will name each field accordingly. For example, the `street` field on
+        # `Address` will be named `user[address][street]`.
+
+        # For situations like this where an association exists between two models, the nested
+        # attributes approach works great. However sometimes all you want is to compose two forms
+        # together that aren't connected by an association. In such cases the fields will still
+        # include the name of the parent model, eg. `user[address][street]` instead of what we want,
+        # `address[street]`. To render the form independent of the parent, pass `nested: false`.
+        def initialize(*fields_for_args, builder:, form:, nested: true, **fields_for_kwargs, &block)
           @fields_for_args = fields_for_args
           @fields_for_kwargs = fields_for_kwargs
+          @nested = nested
           @ref_block = block
 
           super(builder: builder, form: form, **fields_for_kwargs)

lib/primer/forms/form_reference.html.erb

@@ -1,3 +1,3 @@
-<%= builder.fields_for(*@input.fields_for_args, **@input.fields_for_kwargs) do |fields| %>
+<%= builder_or_view.primer_fields_for(*@input.fields_for_args, **@input.fields_for_kwargs) do |fields| %>
   <%= render(@input.ref_block.call(fields)) %>
 <% end %>

lib/primer/forms/form_reference.rb

@@ -9,6 +9,10 @@ class FormReference < BaseComponent
       def initialize(input:)
         @input = input
       end
+
+      def builder_or_view
+        @input.nested? ? builder : @view_context
+      end
     end
   end
 end

test/lib/primer/forms/form_reference_input_test.rb

@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require "lib/test_helper"
+
+class Primer::Forms::FormReferenceInputTest < Minitest::Test
+  include Primer::ComponentTestHelpers
+
+  class UserForm < ApplicationForm
+    form do |user_form|
+      user_form.text_field(name: :first_name, label: "First name")
+      user_form.text_field(name: :last_name, label: "Last name")
+      user_form.fields_for(:address, nested: @nested) do |builder|
+        AddressForm.new(builder)
+      end
+    end
+
+    def initialize(nested:)
+      @nested = nested
+    end
+  end
+
+  class AddressForm < ApplicationForm
+    form do |address_form|
+      address_form.text_field(name: :street, label: "Street")
+      address_form.text_field(name: :city, label: "City")
+      address_form.text_field(name: :state, label: "State")
+    end
+  end
+
+  def test_nests_fields
+    render_in_view_context do
+      primer_form_with(scope: :user, url: "/foo") do |f|
+        render(UserForm.new(f, nested: true))
+      end
+    end
+
+    assert_selector "input[name='user[address][street]']"
+    assert_selector "input[name='user[address][city]']"
+    assert_selector "input[name='user[address][state]']"
+  end
+
+  def test_does_not_nest_fields
+    render_in_view_context do
+      primer_form_with(scope: :user, url: "/foo") do |f|
+        render(UserForm.new(f, nested: false))
+      end
+    end
+
+    assert_selector "input[name='address[street]']"
+    assert_selector "input[name='address[city]']"
+    assert_selector "input[name='address[state]']"
+  end
+end