Display the error text as the abide error

app/cells/decidim/plans/plan_form/contents_edit.erb

@@ -1,5 +1,5 @@
 <% object.contents.each do |content| %>
-  <%= fields_for "contents[#{content.section.id}]", content, namespace: "plans_section_#{content.section.id}" do |content_form| %>
+  <%= fields_for "contents[#{content.section.id}]", content, namespace: "plans_section_#{content.section.id}", builder: Decidim::Plans::FormBuilder do |content_form| %>
     <% content_form.instance_variable_set(:@template, form.instance_variable_get(:@template)) %>
     <% content = content_form.object %>
 

app/cells/decidim/plans/section_edit_cell.rb

@@ -27,7 +27,8 @@ def field_options(name = :body)
           id: field_id(name),
           label: false,
           disabled: field_disabled?,
-          help_text: tooltip_help? ? nil : model.help
+          help_text: tooltip_help? ? nil : model.help,
+          abide_error: translated_attribute(model.section.error_text).presence
         }
       end
 

app/cells/decidim/plans/section_type_edit/field_category_cell.rb

@@ -34,6 +34,7 @@ def categories_select(form, name, collection, options = {}, html_options = {})
           selected = form.object.send(name)
           selected = selected.first if selected.is_a?(Array) && selected.length > 1
           categories = categories_for_select(collection)
+          options[:abide_error] ||= translated_attribute(section.error_text).presence
 
           form.select(name, options_for_select(categories, selected), options, html_options)
         end

app/cells/decidim/plans/section_type_edit/field_scope_cell.rb

@@ -23,6 +23,7 @@ def show
         # Returns nothing.
         def scopes_picker_field(form, name, options: {}, html_options: {})
           options[:label] ||= translated_attribute(section.body) if options[:label].nil?
+          options[:abide_error] ||= translated_attribute(section.error_text).presence
           form.select(name, scopes_options(scopes_root), options, html_options)
         end
 

lib/decidim/plans.rb

@@ -22,6 +22,7 @@ module Plans
     autoload :SectionTypeRegistry, "decidim/plans/section_type_registry"
     autoload :LayoutManifest, "decidim/plans/layout_manifest"
     autoload :LayoutRegistry, "decidim/plans/layout_registry"
+    autoload :FormBuilder, "decidim/plans/form_builder"
 
     include ActiveSupport::Configurable
 

lib/decidim/plans/form_builder.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+module Decidim
+  module Plans
+    class FormBuilder < Decidim::FormBuilder
+      private
+
+      # Customized to modify the options passed to abide.
+      def field_with_validations(attribute, options, html_options)
+        class_options = html_options || options
+
+        if error?(attribute)
+          class_options[:class] = class_options[:class].to_s
+          class_options[:class] += " is-invalid-input"
+        end
+
+        help_text = options.delete(:help_text)
+        abide_error = options.delete(:abide_error)
+        prefix = options.delete(:prefix)
+        postfix = options.delete(:postfix)
+
+        class_options = extract_validations(attribute, options).merge(class_options)
+
+        content = yield(class_options)
+        content += abide_error_element(attribute, abide_error) if class_options[:pattern] || class_options[:required]
+        content = content.html_safe
+
+        html = wrap_prefix_and_postfix(content, prefix, postfix)
+        html + error_and_help_text(attribute, options.merge(help_text: help_text))
+      end
+
+      def abide_error_element(attribute, abide_error = nil)
+        return super(attribute) if abide_error.blank?
+
+        # Override the abide text
+        content_tag(:span, abide_error, class: "form-error")
+      end
+    end
+  end
+end