Capture same base path error and display to user

Instead of presenting a server error to the user if they try and create
an edition that has the base path of another published edition, the
error is now presented to the user.

Author: ChrisBAshton

app/controllers/admin/editions_controller.rb

@@ -93,6 +93,9 @@ def create
       build_edition_dependencies
       render :new
     end
+  rescue Whitehall::UnpublishableInstanceError => _e
+    construct_similar_slug_warning_error
+    render :new
   end
 
   def edit

app/models/call_for_evidence.rb

@@ -48,6 +48,10 @@ def process_associations_after_save(edition)
     schedule_republishing_workers
   end
 
+  def self.base_path
+    "/government/calls-for-evidence/"
+  end
+
   def schedule_republishing_workers
     if opening_at.try(:future?)
       PublishingApiDocumentRepublishingWorker
@@ -131,10 +135,6 @@ def string_for_slug
     title
   end
 
-  def base_path
-    "/government/calls-for-evidence/#{slug}"
-  end
-
   def publishing_api_presenter
     PublishingApi::CallForEvidencePresenter
   end

app/models/case_study.rb

@@ -10,6 +10,10 @@ class CaseStudy < Edition
   include Edition::WorldwideOrganisations
   include Edition::LeadImage
 
+  def self.base_path
+    "/government/case-studies/"
+  end
+
   def rendering_app
     Whitehall::RenderingApp::FRONTEND
   end
@@ -18,10 +22,6 @@ def translatable?
     !non_english_edition?
   end
 
-  def base_path
-    "/government/case-studies/#{slug}"
-  end
-
   def publishing_api_presenter
     PublishingApi::CaseStudyPresenter
   end

app/models/consultation.rb

@@ -58,6 +58,10 @@ def process_associations_after_save(edition)
     schedule_republishing_workers
   end
 
+  def self.base_path
+    "/government/consultations/"
+  end
+
   def schedule_republishing_workers
     if opening_at.try(:future?)
       PublishingApiDocumentRepublishingWorker
@@ -145,10 +149,6 @@ def string_for_slug
     title
   end
 
-  def base_path
-    "/government/consultations/#{slug}"
-  end
-
   def publishing_api_presenter
     PublishingApi::ConsultationPresenter
   end

app/models/detailed_guide.rb

@@ -11,6 +11,10 @@ class DetailedGuide < Edition
   include Edition::RelatedDocuments
   include Edition::TopicalEvents
 
+  def self.base_path
+    "/guidance/"
+  end
+
   has_many :related_mainstreams, foreign_key: "edition_id", dependent: :destroy
 
   validate :related_mainstream_found, if: :related_mainstream_requested?
@@ -104,10 +108,6 @@ def all_nation_applicability_selected?
     newly_created ? false : all_nation_applicability
   end
 
-  def base_path
-    "/guidance/#{slug}"
-  end
-
   def publishing_api_presenter
     PublishingApi::DetailedGuidePresenter
   end

app/models/document.rb

@@ -85,12 +85,9 @@ def first_edition_id
 
   def similar_slug_exists?
     scope = Document.where(document_type:)
-    sequence_separator = friendly_id_config.sequence_separator
 
-    # slug is a nullable column, so we can't assume that it exists
-    return false if slug.nil?
-
-    slug_without_sequence = slug.split(sequence_separator).first
+    # return false if slug.nil?
+    return false if slug_without_sequence.blank?
 
     scope.where(
       "slug IN (?) OR slug LIKE ?",
@@ -99,6 +96,17 @@ def similar_slug_exists?
     ).count > 1
   end
 
+  def slug_without_sequence
+    # slug is a nullable column, so we can't assume that it exists
+    return if slug.nil?
+
+    slug.split(sequence_separator).first
+  end
+
+  def sequence_separator
+    friendly_id_config.sequence_separator
+  end
+
   def should_generate_new_friendly_id?
     sluggable_string.present?
   end

app/models/document_collection.rb

@@ -22,6 +22,10 @@ def process_associations_before_save(new_edition)
 
   add_trait ClonesGroupsTrait
 
+  def self.base_path
+    "/government/collections/"
+  end
+
   def rendering_app
     Whitehall::RenderingApp::FRONTEND
   end
@@ -34,10 +38,6 @@ def locale_can_be_changed?
     true
   end
 
-  def base_path
-    "/government/collections/#{slug}"
-  end
-
   def publishing_api_presenter
     PublishingApi::DocumentCollectionPresenter
   end

app/models/edition.rb

@@ -101,6 +101,10 @@ def self.scheduled_for_publication_as(slug)
     document&.scheduled_edition
   end
 
+  def self.base_path
+    "/government/generic-editions/"
+  end
+
   def skip_main_validation?
     FROZEN_STATES.include?(state)
   end
@@ -396,10 +400,11 @@ def attribute_names
   end
 
   def base_path
-    url_slug = slug || id.to_param
-    "/government/generic-editions/#{url_slug}"
+    "#{self.class.base_path}#{url_slug}"
   end
 
+  delegate :slug_without_sequence, to: :document
+
   def public_path(options = {})
     return if base_path.nil?
 
@@ -442,6 +447,10 @@ def deleted_associated_documents
 
 private
 
+  def url_slug
+    slug || id.to_param
+  end
+
   def date_for_government
     published_edition_date = first_public_at.try(:to_date)
     draft_edition_date = updated_at.try(:to_date)

app/models/fatality_notice.rb

@@ -25,6 +25,10 @@ def process_associations_after_save(new_edition)
 
   add_trait CasualtiesTrait
 
+  def self.base_path
+    "/government/fatalities/"
+  end
+
   def has_operational_field?
     true
   end
@@ -33,10 +37,6 @@ def rendering_app
     Whitehall::RenderingApp::FRONTEND
   end
 
-  def base_path
-    "/government/fatalities/#{slug}"
-  end
-
   def publishing_api_presenter
     PublishingApi::FatalityNoticePresenter
   end

app/services/draft_edition_updater.rb

@@ -8,6 +8,8 @@ def perform!
   end
 
   def failure_reason
+    return @failure_reason if @failure_reason.present?
+
     if !edition.pre_publication?
       "A #{edition.state} edition may not be updated."
     elsif should_check_current_user_will_retain_access? && access_limit_excludes_current_user?