Improve comment parse performance

## Benchmark (Comparison with rexml 3.4.1)
```
$ benchmark-driver benchmark/parse_comment.yaml
Calculating -------------------------------------
                     rexml 3.4.1      master  3.4.1(YJIT)  master(YJIT)
           top_level     938.694      3.947k      875.350        2.853k i/s -     100.000 times in 0.106531s 0.025336s 0.114240s 0.035046s
          in_doctype     988.445      3.896k      926.836        2.860k i/s -     100.000 times in 0.101169s 0.025670s 0.107894s 0.034963s
       after_doctype     610.627      1.223k      546.379        1.049k i/s -     100.000 times in 0.163766s 0.081783s 0.183023s 0.095290s

Comparison:
                        top_level
              master:      3947.0 i/s
        master(YJIT):      2853.4 i/s - 1.38x  slower
         rexml 3.4.1:       938.7 i/s - 4.20x  slower
         3.4.1(YJIT):       875.4 i/s - 4.51x  slower

                       in_doctype
              master:      3895.6 i/s
        master(YJIT):      2860.2 i/s - 1.36x  slower
         rexml 3.4.1:       988.4 i/s - 3.94x  slower
         3.4.1(YJIT):       926.8 i/s - 4.20x  slower

                    after_doctype
              master:      1222.7 i/s
        master(YJIT):      1049.4 i/s - 1.17x  slower
         rexml 3.4.1:       610.6 i/s - 2.00x  slower
         3.4.1(YJIT):       546.4 i/s - 2.24x  slower
```

- YJIT=ON : 1.91x - 3.25x faster
- YJIT=OFF : 2.00x - 4.20x faster

Author: naitoh

benchmark/parse_comment.yaml

@@ -0,0 +1,44 @@
+loop_count: 100
+contexts:
+  - gems:
+      rexml: 3.2.6
+    require: false
+    prelude: require 'rexml'
+  - name: master
+    prelude: |
+      $LOAD_PATH.unshift(File.expand_path("lib"))
+      require 'rexml'
+  - name: 3.2.6(YJIT)
+    gems:
+      rexml: 3.2.6
+    require: false
+    prelude: |
+      require 'rexml'
+      RubyVM::YJIT.enable
+  - name: master(YJIT)
+    prelude: |
+      $LOAD_PATH.unshift(File.expand_path("lib"))
+      require 'rexml'
+      RubyVM::YJIT.enable
+
+prelude: |
+  require 'rexml/document'
+
+  SIZE = 100000
+
+  def top_level_xml
+    "<!--" + "a" * SIZE + "-->\n"
+  end
+
+  def in_doctype_xml
+    "<!DOCTYPE foo [<!--" + "a" * SIZE + "-->]>"
+  end
+
+  def after_doctype_xml
+    "<root/><!--" + "a" * SIZE + "-->"
+  end
+
+benchmark:
+  'top_level'      : REXML::Document.new(top_level_xml)
+  'in_doctype'     : REXML::Document.new(in_doctype_xml)
+  'after_doctype'  : REXML::Document.new(after_doctype_xml)

lib/rexml/parsers/baseparser.rb

@@ -277,14 +277,7 @@ def pull_event
             return process_instruction
           elsif @source.match?("<!", true)
             if @source.match?("--", true)
-              md = @source.match(/(.*?)-->/um, true)
-              if md.nil?
-                raise REXML::ParseException.new("Unclosed comment", @source)
-              end
-              if /--|-\z/.match?(md[1])
-                raise REXML::ParseException.new("Malformed comment", @source)
-              end
-              return [ :comment, md[1] ]
+              return [ :comment, process_comment ]
             elsif @source.match?("DOCTYPE", true)
               base_error_message = "Malformed DOCTYPE"
               unless @source.match?(/\s+/um, true)
@@ -417,12 +410,8 @@ def pull_event
                 raise REXML::ParseException.new(message, @source)
               end
               return [:notationdecl, name, *id]
-            elsif md = @source.match(/--(.*?)-->/um, true)
-              case md[1]
-              when /--/, /-\z/
-                raise REXML::ParseException.new("Malformed comment", @source)
-              end
-              return [ :comment, md[1] ] if md
+            elsif @source.match?("--", true)
+              return [ :comment, process_comment ]
             end
           elsif match = @source.match(/(%.*?;)\s*/um, true)
             return [ :externalentity, match[1] ]
@@ -463,14 +452,8 @@ def pull_event
               md = @source.match(/([^>]*>)/um)
               #STDERR.puts "SOURCE BUFFER = #{source.buffer}, #{source.buffer.size}"
               raise REXML::ParseException.new("Malformed node", @source) unless md
-              if md[0][0] == ?-
-                md = @source.match(/--(.*?)-->/um, true)
-
-                if md.nil? || /--|-\z/.match?(md[1])
-                  raise REXML::ParseException.new("Malformed comment", @source)
-                end
-
-                return [ :comment, md[1] ]
+              if @source.match?("--", true)
+                return [ :comment, process_comment ]
               elsif @source.match?("[CDATA[", true)
                 text = @source.read_until("]]>")
                 if text.chomp!("]]>")
@@ -738,6 +721,18 @@ def parse_id_invalid_details(accept_external_id:,
         end
       end
 
+      def process_comment
+        text = @source.read_until("-->")
+        unless text.chomp!("-->")
+          raise REXML::ParseException.new("Unclosed comment: Missing end '-->'", @source)
+        end
+
+        if text.include? "--" or text.end_with?("-")
+          raise REXML::ParseException.new("Malformed comment", @source)
+        end
+        text
+      end
+
       def process_instruction
         name = parse_name("Malformed XML: Invalid processing instruction node")
         if @source.match?(/\s+/um, true)

test/parse/test_comment.rb

@@ -17,7 +17,7 @@ def test_toplevel_unclosed_comment
           parse("<!--")
         end
         assert_equal(<<~DETAIL, exception.to_s)
-          Unclosed comment
+          Unclosed comment: Missing end '-->'
           Line: 1
           Position: 4
           Last 80 unconsumed characters:
@@ -48,6 +48,18 @@ def test_toplevel_malformed_comment_end
         DETAIL
       end
 
+      def test_doctype_unclosed_comment
+        exception = assert_raise(REXML::ParseException) do
+          parse("<!DOCTYPE foo [<!--")
+        end
+        assert_equal(<<~DETAIL, exception.to_s)
+          Unclosed comment: Missing end '-->'
+          Line: 1
+          Position: 19
+          Last 80 unconsumed characters:
+        DETAIL
+      end
+
       def test_doctype_malformed_comment_inner
         exception = assert_raise(REXML::ParseException) do
           parse("<!DOCTYPE foo [<!-- -- -->")
@@ -72,16 +84,15 @@ def test_doctype_malformed_comment_end
         DETAIL
       end
 
-      def test_after_doctype_malformed_comment_short
+      def test_after_doctype_unclosed_comment
         exception = assert_raise(REXML::ParseException) do
           parse("<a><!-->")
         end
-        assert_equal(<<~DETAIL.chomp, exception.to_s)
-          Malformed comment
+        assert_equal(<<~DETAIL, exception.to_s)
+          Unclosed comment: Missing end '-->'
           Line: 1
           Position: 8
           Last 80 unconsumed characters:
-          -->
         DETAIL
       end