Avoid infinity loop when empty string pattern

2 files changed, 16 insertions, 10 deletions

diff --git a/mrblib/string.rb b/mrblib/string.rb
index b13cfd69a..0f65c9c97 100644
--- a/mrblib/string.rb
+++ b/mrblib/string.rb
@@ -52,17 +52,22 @@ class String
   # ISO 15.2.10.5.18
   def gsub(*args, &block)
     if args.size == 2
-      s = ""
-      i = 0
-      while j = index(args[0], i)
-        seplen = args[0].length
-        k = j + seplen
-        pre = self[0, j]
-        post = self[k, length-k]
-        s += self[i, j-i] + args[1].__sub_replace(pre, args[0], post)
-        i = k
+      pattern, replace = *args
+      plen = pattern.length
+      replace = replace.to_str
+      offset = 0
+      result = []
+      while found = index(pattern, offset)
+        result << self[offset, found - offset]
+        offset = found + plen
+        result << replace.__sub_replace(self[0, found], pattern, self[offset..-1] || "")
+        if plen == 0
+          result << self[offset, 1]
+          offset += 1
+        end
       end
-      s + self[i, length-i]
+      result << self[offset..-1] if offset < length
+      result.join
     elsif args.size == 1 && block
       split(args[0], -1).join(block.call(args[0]))
     else
diff --git a/test/t/string.rb b/test/t/string.rb
index 442c95bf7..e39eefb60 100644
--- a/test/t/string.rb
+++ b/test/t/string.rb
@@ -365,6 +365,7 @@ assert('String#gsub', '15.2.10.5.18') do
   assert_equal('$$a$$',  '##a##'.gsub('##'){|w| '$$' }, 'mruby/mruby#847 another case with block')
   assert_equal('A',      'a'.gsub('a', 'A'))
   assert_equal('A',      'a'.gsub('a'){|w| w.capitalize })
+  assert_equal(".h.e.l.l.o.", "hello".gsub("", "."))
 end
 
 assert('String#gsub with backslash') do