add Hash#rehash to handle key modification; ref #2945

mrblib/hash.rb

@@ -319,6 +319,29 @@ class Hash
     h
   end
 
+  ##
+  #  call-seq:
+  #    hsh.rehash -> hsh
+  #
+  #  Rebuilds the hash based on the current hash values for each key. If
+  #  values of key objects have changed since they were inserted, this
+  #  method will reindex <i>hsh</i>.
+  #
+  #     h = {"AAA" => "b"}
+  #     h.keys[0].chop!
+  #     h          #=> {"AA"=>"b"}
+  #     h["AA"]    #=> nil
+  #     h.rehash   #=> {"AA"=>"b"}
+  #     h["AA"]    #=> "b"
+  #
+  def rehash
+    h = {}
+    self.each{|k,v|
+      h[k] = v
+    }
+    self.replace(h)
+  end
+
   def __update(h)
     h.each_key{|k| self[k] = h[k]}
     self

test/t/hash.rb

@@ -342,3 +342,12 @@ assert('Hash#inspect') do
   assert_include ret, '"a"=>100'
   assert_include ret, '"d"=>400'
 end
+
+assert('Hash#rehash') do
+  h = {[:a] => "b"}
+  # hash key modified
+  h.keys[0][0] = :b
+  # h[[:b]] => nil
+  h.rehash
+  assert_equal("b", h[[:b]])
+end