Patch GovukTechDocs::TechDocsHTMLRenderer

Add a new `preprocess` hook to the Redcarpet renderer to reset the ID generator.
This ensures headings that may appear on multiple pages are not treated as duplicate
when rendering one of these pages.

See: alphagov/tech-docs-gem#310

config.rb

@@ -1,6 +1,11 @@
 require "govuk_tech_docs"
 require "lib/sassdocs_helpers"
 
+# Patch the GovukTechDocs cleanly
+# https://www.justinweiss.com/articles/3-ways-to-monkey-patch-without-making-a-mess/
+require "lib/ext/govuk_tech_docs/tech_docs_html_renderer/reset_unique_identifier_generator_preprocess"
+GovukTechDocs::TechDocsHTMLRenderer.include Ext::GovukTechDocs::TechDocsHTMLRenderer::ResetUniqueIndentifierGeneratorPreprocess
+
 config[:build_dir] = "deploy/public"
 
 GovukTechDocs.configure(self)

lib/ext/govuk_tech_docs/tech_docs_html_renderer/reset_unique_identifier_generator_preprocess.rb

@@ -0,0 +1,25 @@
+module Ext
+  module GovukTechDocs
+    module TechDocsHTMLRenderer
+      module ResetUniqueIndentifierGeneratorPreprocess
+        ##
+        # Fix for the unique ID generation not being reset for each document
+        # leading to IDs being considered duplicates when on different pages
+        # while they shouldn't be
+        #
+        # @see https://github.com/alphagov/tech-docs-gem/issues/310
+
+        def preprocess(document)
+          ##
+          # Resets the UniqueIdentifierGenerator before the document gets processed
+          #
+          # @see https://github.com/vmg/redcarpet#prepost-process
+
+          ::GovukTechDocs::UniqueIdentifierGenerator.instance.reset
+
+          document
+        end
+      end
+    end
+  end
+end

source/javascript-api-reference/index.html.md.erb

@@ -30,7 +30,7 @@ GOVUKFrontend.initAll({
 })
 ```
 
-## Accordion component
+## Accordion
 
 ### i18n
 
@@ -117,7 +117,7 @@ Default:
 "Show this section"
 ```
 
-## Button component
+## Button
 
 ### preventDoubleClick
 
@@ -131,7 +131,7 @@ Default:
 false
 ```
 
-## CharacterCount component
+## CharacterCount
 
 ### maxlength
 
@@ -287,7 +287,7 @@ Default:
 }
 ```
 
-## ErrorSummary component
+## ErrorSummary
 
 ### disableAutoFocus
 
@@ -301,7 +301,7 @@ Default
 false
 ```
 
-## NotificationBanner component
+## NotificationBanner
 
 ### `disableAutoFocus`