made colorizer filter fail if necessary executables are not present

--HG--
branch : 3.1.x

Author: denisdefreyne

lib/nanoc3/filters/colorize_syntax.rb

@@ -1,5 +1,7 @@
 # encoding: utf-8
 
+require 'open3'
+
 module Nanoc3::Filters
   class ColorizeSyntax < Nanoc3::Filter
 
@@ -93,6 +95,8 @@ def dummy(code, language, params={})
     end
 
     def pygmentize(code, language, params={})
+      check_availability('pygmentize --V')
+
       IO.popen("pygmentize -l #{language} -f html", "r+") do |io|
         io.write(code)
         io.close_write
@@ -103,5 +107,10 @@ def pygmentize(code, language, params={})
       end
     end
 
+    def check_availability(cmd)
+      # Will raise on error
+      Open3.popen3('highlight --version') { |stdin, stdout, stderr| }
+    end
+
   end
 end

test/filters/test_colorize_syntax.rb

@@ -53,4 +53,32 @@ def test_pygmentize
     assert_match(expected_output, actual_output)
   end
 
+  def test_colorize_syntax_with_missing_executables
+    if_have 'nokogiri' do
+      begin
+        original_path = ENV['PATH']
+        ENV['PATH'] = './blooblooblah'
+
+        # Create filter
+        filter = ::Nanoc3::Filters::ColorizeSyntax.new
+
+        # Get input and expected output
+        input = '<pre><code class="language-ruby">puts "foo"</code></pre>'
+
+        # Run filter
+        begin
+          input = '<pre><code class="language-ruby">puts "foo"</code></pre>'
+          actual_output = filter.run(
+            input,
+            :colorizers => { :ruby => :pygmentize })
+          flunk "expected colorizer to raise if no executable is available"
+        rescue => e
+          assert_match /No such file or directory/, e.message
+        end
+      ensure
+        ENV['PATH'] = original_path
+      end
+    end
+  end
+
 end