Fail build on unexpected manual change

Rakefile

@@ -23,6 +23,7 @@ desc "Generate the 'Prawn by Example' manual"
 task :manual do
   puts 'Building manual...'
   require File.expand_path(File.join(__dir__, %w[manual contents]))
+  prawn_manual_document.render_file('manual.pdf')
   puts 'The Prawn manual is available at manual.pdf. Happy Prawning!'
 end
 

manual/contents.rb

@@ -2,28 +2,32 @@
 
 require_relative 'example_helper'
 
-Encoding.default_external = Encoding::UTF_8
+def prawn_manual_document
+  old_default_external_encoding = Encoding.default_external
+  Encoding.default_external = Encoding::UTF_8
 
-Prawn::ManualBuilder::Example.generate(
-  'manual.pdf',
-  skip_page_creation: true,
-  page_size: 'FOLIO'
-) do
-  load_page '', 'cover'
-  load_page '', 'how_to_read_this_manual'
+  Prawn::ManualBuilder::Example.new(
+    skip_page_creation: true,
+    page_size: 'FOLIO'
+  ) do
+    load_page '', 'cover'
+    load_page '', 'how_to_read_this_manual'
 
-  # Core chapters
-  load_package 'basic_concepts'
-  load_package 'graphics'
-  load_package 'text'
-  load_package 'bounding_box'
+    # Core chapters
+    load_package 'basic_concepts'
+    load_package 'graphics'
+    load_package 'text'
+    load_package 'bounding_box'
 
-  # Remaining chapters
-  load_package 'layout'
-  load_page '', 'table'
-  load_package 'images'
-  load_package 'document_and_page_options'
-  load_package 'outline'
-  load_package 'repeatable_content'
-  load_package 'security'
+    # Remaining chapters
+    load_package 'layout'
+    load_page '', 'table'
+    load_package 'images'
+    load_package 'document_and_page_options'
+    load_package 'outline'
+    load_package 'repeatable_content'
+    load_package 'security'
+  end
+ensure
+  Encoding.default_external = old_default_external_encoding
 end

manual/cover.rb

@@ -27,12 +27,14 @@
     git_commit = ''
   end
 
-  formatted_text_box(
-    [{
-      text: "Last Update: #{Time.now.strftime('%Y-%m-%d')}\n" \
-        "Prawn Version: #{Prawn::VERSION}\n#{git_commit}",
-      size: 12
-    }],
-    at: [390, cursor - 620]
-  )
+  unless ENV['CI']
+    formatted_text_box(
+      [{
+        text: "Last Update: #{Time.now.strftime('%Y-%m-%d')}\n" \
+          "Prawn Version: #{Prawn::VERSION}\n#{git_commit}",
+        size: 12
+      }],
+      at: [390, cursor - 620]
+    )
+  end
 end

spec/manual_spec.rb

@@ -0,0 +1,33 @@
+require 'spec_helper'
+require 'digest/sha2'
+
+# rubocop: disable Metrics/LineLength
+MANUAL_HASH =
+  case RUBY_ENGINE
+  when 'ruby'
+    '6aae613c48e7d9f7d4f57f026fe7c70eddff0bda8698ce7e8720bcd8c72ba1ca48f795aff153c39669e9282ee7350aeeabc39dd7051269cba95ae4a06e7437c8'
+  when 'jruby'
+    '483874116106a5f6276a1f196c6e72f9f823c613108512431d4e805ef5f03387d7a1a05a481540eebde8f86cba254f231d5b56872857c2e27900effccd2804f9'
+  end
+# rubocop: enable Metrics/LineLength
+
+RSpec.describe Prawn do
+  describe 'manual' do
+    # JRuby's zlib is a bit quirky. It sometimes produces different output to
+    # libzlib (used by MRI). It's still a proper deflate stream and can be
+    # decompressed just fine but for whatever reason compressin produses
+    # different output.
+    #
+    # See: https://github.com/jruby/jruby/issues/4244
+    it 'contains no unexpected changes' do
+      ENV['CI'] ||= 'true'
+
+      require File.expand_path(File.join(__dir__, %w[.. manual contents]))
+      s = prawn_manual_document.render
+
+      hash = Digest::SHA512.hexdigest(s)
+
+      expect(hash).to eq MANUAL_HASH
+    end
+  end
+end