Fix crash in Terminal256 formatter with escaped tokens (#1402)

Escaped tokens were causing a crash in the 256-color terminal formatter.
This commit fixes the bug and adds tests.

lib/rouge/formatters/terminal256.rb

@@ -24,10 +24,7 @@ def initialize(theme = Themes::ThankfulEyes.new)
 
       def stream(tokens, &b)
         tokens.each do |tok, val|
-          escape = escape_sequence(tok)
-          yield escape.style_string
-          yield val.gsub("\n", "#{escape.reset_string}\n#{escape.style_string}")
-          yield escape.reset_string
+          escape_sequence(tok).stream_value(val, &b)
         end
       end
 
@@ -85,6 +82,14 @@ def bg
           @bg = style.bg && self.class.color_index(style.bg)
         end
 
+
+        def stream_value(val, &b)
+          yield style_string
+          yield val.gsub("\n", "#{reset_string}\n#{style_string}")
+                   .gsub("\e", "\\e")
+          yield reset_string
+        end
+
         def style_string
           @style_string ||= begin
             attrs = []
@@ -157,9 +162,16 @@ def self.closest_color(r, g, b)
         end
       end
 
+      class Unescape < EscapeSequence
+        def initialize(*) end
+        def style_string(*) '' end
+        def reset_string(*) '' end
+        def stream_value(val) yield val end
+      end
+
     # private
       def escape_sequence(token)
-        return '' if escape?(token)
+        return Unescape.new if escape?(token)
         @escape_sequences ||= {}
         @escape_sequences[token.qualname] ||=
           EscapeSequence.new(get_style(token))

spec/lexers/escape_spec.rb

@@ -0,0 +1,26 @@
+describe Rouge::Lexers::Escape do
+  let(:lexer) { Rouge::Lexers::Escape.new(lang: 'json') }
+  let(:text) { '{ "foo": <!<bar>!> }' }
+  let(:result) {
+    Rouge::Formatter.with_escape do
+      formatter.format(lexer.lex(text))
+    end
+  }
+
+  describe 'html' do
+    let(:formatter) { Rouge::Formatters::HTML.new }
+
+    it 'unescapes' do
+      assert { result =~ /<bar>/ }
+    end
+  end
+
+  describe 'terminal256' do
+    let(:formatter) { Rouge::Formatters::Terminal256.new }
+    let(:text) { %({ "foo": <!\e123!> }) }
+
+    it 'unescapes' do
+      assert { result =~ /\e123/ }
+    end
+  end
+end