Fix label for attribute when not scoped to model (#3696)

Author: myabc

.changeset/chatty-pants-hang.md

@@ -0,0 +1,5 @@
+---
+'@primer/view-components': patch
+---
+
+Fix incorrect label `for` attribute value when `scope_id_to_model: false`

app/lib/primer/forms/dsl/input.rb

@@ -61,7 +61,6 @@ def initialize(builder:, form:, **system_arguments)
           @input_arguments = system_arguments
           @input_arguments.delete(:id) unless @input_arguments[:id].present?
           @label_arguments = @input_arguments.delete(:label_arguments) || {}
-          @label_arguments[:for] = id if id.present?
 
           @label_arguments[:class] = class_names(
             @label_arguments[:class],
@@ -105,6 +104,11 @@ def initialize(builder:, form:, **system_arguments)
           end
           # rubocop:enable Style/IfUnlessModifier
 
+          # Only set `for` when the id is known. Otherwise leave it unset so
+          # Rails generates the scoped id for both label and input; passing
+          # `for: nil` would suppress that and drop the association.
+          @label_arguments[:for] = @input_arguments[:id] if @input_arguments[:id].present?
+
           # Whether or not to wrap the component in a FormControl, which renders a
           # label above and validation message beneath the input.
           @form_control = @input_arguments.delete(:form_control) { true }

test/lib/primer/forms/input_test.rb

@@ -104,6 +104,7 @@ def test_removes_model_scope_from_name_and_id
     end
 
     assert_selector "input#ultimate_answer[name=ultimate_answer]"
+    assert_selector "label[for=ultimate_answer]"
   end
 
   def test_uses_given_id
@@ -116,5 +117,28 @@ def test_uses_given_id
     end
 
     assert_selector "input#foobar[name=ultimate_answer]"
+    assert_selector "label[for=foobar]"
+  end
+
+  class ModelScopeForm < ApplicationForm
+    form do |model_scope_form|
+      model_scope_form.text_field(
+        name: :ultimate_answer,
+        label: "Ultimate answer"
+      )
+    end
+  end
+
+  def test_label_for_matches_scoped_id_by_default
+    model = DeepThought.new(42)
+
+    render_in_view_context do
+      primer_form_with(model: model, url: "/foo") do |f|
+        render(ModelScopeForm.new(f))
+      end
+    end
+
+    assert_selector "input#deep_thought_ultimate_answer[name='deep_thought[ultimate_answer]']"
+    assert_selector "label[for=deep_thought_ultimate_answer]"
   end
 end