WIP: Add support for new absence operator

absent_operator.patch

diff --git a/lib/regexp_parser/scanner/scanner.rl b/lib/regexp_parser/scanner/scanner.rl
index e200cfc..96b2e70 100644
--- a/lib/regexp_parser/scanner/scanner.rl
+++ b/lib/regexp_parser/scanner/scanner.rl
@@ -78,6 +78,8 @@
 
   conditional           = '(?(';
 
+  absent_operator       = '?~';
+
   group_comment         = '?#' . [^)]* . group_close;
 
   group_atomic          = '?>';
@@ -540,6 +542,12 @@
       emit(:group, :comment, *text(data, ts, te))
     };
 
+    # (?~exp) absent operator:
+    # ------------------------------------------------------------------------
+    group_open . absent_operator >group_opened {
+      p = scan_absent_operator(p, data, ts, te)
+    };
+
     # Expression options:
     #   (?imxdau-imx)         option on/off
     #                         i: ignore case
@@ -930,6 +938,41 @@ module Regexp::Scanner
     p # return the new value of the data pointer
   end
 
+  def self.scan_absent_operator(p, data, ts, te)
+    text = text(data, ts, te).first
+
+    exp_char, exp_length = true, 0
+
+    emit(:absent_op, :open, text(data, ts, te).first, ts, te)
+
+    # Copy until a closing parenthesis, skipping escaped ones.
+    while exp_char
+      if data[te + exp_length]
+        c = data[te + exp_length].chr
+
+        if c == '\\'
+          text << c ; p += 1 ; exp_length += 1
+
+          c = data[te + exp_length].chr
+
+          text << c ; p += 1 ; exp_length += 1
+        elsif c == ')'
+          exp_char = false
+
+          emit(:absent_op, :expression, text, ts, te + exp_length)
+         #emit(:absent_op, :close, c, ts, te + exp_length)
+
+        else
+          text << c ; p += 1 ; exp_length += 1
+        end
+      else
+        raise PrematureEndError.new("absent operator `#{text}'")
+      end
+    end
+
+    p
+  end
+
   # Copy from ts to te from data as text
   def self.copy(data, range)
     data[range].pack('c*')
diff --git a/test/scanner/test_groups.rb b/test/scanner/test_groups.rb
index 5dabb56..aa7062e 100644
--- a/test/scanner/test_groups.rb
+++ b/test/scanner/test_groups.rb
@@ -55,6 +55,15 @@ class ScannerGroups < Test::Unit::TestCase
     })
   end
 
+  if RUBY_VERSION >= '2.4.1'
+    tests.merge!({
+      # Absent operator
+      '(?~abc)'         => [0, :absent_op, :open,       '(?~',  0, 7],
+      '(?~def)'         => [1, :absent_op, :expression, 'def',  0, 7],
+      '(?~xyz)'         => [2, :absent_op, :close,      ')',    0, 7],
+    })
+  end
+
   tests.each_with_index do |(pattern, (index, type, token, text, ts, te)), count|
     define_method "test_scanner_#{type}_#{token}_#{count}" do
       tokens = RS.scan(pattern)
diff --git a/test/warnings.yml b/test/warnings.yml
index e957c37..f1616c8 100644
--- a/test/warnings.yml
+++ b/test/warnings.yml
@@ -1,6 +1,6 @@
 ---
 # Unused variable emitted by ragel
-- "lib/regexp_parser/scanner.rb:1674: warning:
+- "lib/regexp_parser/scanner.rb:1677: warning:
   assigned but unused variable - testEof"
 
 # Unavoidable duplicated character range tests