Escape unescaped backslash at the end of code

Fix #1402

Author: nobu

lib/rdoc/markdown.kpeg

@@ -497,6 +497,15 @@
     end
   end
 
+  ##
+  # Wraps `text` in code markup for rdoc inline formatting
+
+  def code text
+    # escape unescaped backslash at the end
+    backslash_at_end = "\\" if /(?<!\\)(?:\\\\)*\\\z/.match?(text)
+    "<code>#{text}#{backslash_at_end}</code>"
+  end
+
   ##
   # Parses inline markdown in table cells
 
@@ -1129,7 +1138,7 @@ Code = ( Ticks1 @Sp < (
            !( @Sp Ticks5 ) ( @Spacechar | @Newline !@BlankLine )
          )+ > @Sp Ticks5
        )
-       { "<code>#{text}</code>" }
+       { code text }
 
 RawHtml = < (HtmlComment | HtmlBlockScript | HtmlTag) >
           { if html? then text else '' end }

test/rdoc/rdoc_markdown_test.rb

@@ -158,6 +158,34 @@ def test_parse_code
     doc = parse "Code: ``` text`s ```"
     expected = doc(para("Code: <code>text`s</code>"))
     assert_equal expected, doc
+
+    doc = parse "Code: `\\`"
+    expected = doc(para("Code: <code>\\\\</code>"))
+    assert_equal expected, doc
+
+    doc = parse "Code: ` \\ `"
+    expected = doc(para("Code: <code>\\\\</code>"))
+    assert_equal expected, doc
+
+    doc = parse "Code: `\\`s`"
+    expected = doc(para("Code: <code>\\\\</code>s`"))
+    assert_equal expected, doc
+
+    doc = parse "Code: ``\\`s``"
+    expected = doc(para("Code: <code>\\`s</code>"))
+    assert_equal expected, doc
+
+    doc = parse "Code: `` \\`s ``"
+    expected = doc(para("Code: <code>\\`s</code>"))
+    assert_equal expected, doc
+
+    doc = parse "Code: ```\\`s```"
+    expected = doc(para("Code: <code>\\`s</code>"))
+    assert_equal expected, doc
+
+    doc = parse "Code: ``` \\`s ```"
+    expected = doc(para("Code: <code>\\`s</code>"))
+    assert_equal expected, doc
   end
 
   def test_parse_code_github