core: ported regex.gsub to faster native version (#1233)

* added regex.gmatch iterator and other fixes
* fixed issues reported by Guldoman
* push strings with fixed len just in case for binary safety
* added limit to regex.gsub and use pushinteger
* added description to regex.gsub limits param
* replaced substitutions regex description for correctness
* ignore negative limits on regex.gsub

data/core/regex.lua

@@ -80,63 +80,3 @@ regex.find = function(pattern, str, offset, options)
   end
   return table.unpack(out)
 end
-
--- Will iterate back through any UTF-8 bytes so that we don't replace bits
--- mid character.
-local function previous_character(str, index)
-  local byte
-  repeat
-    index = index - 1
-    byte = string.byte(str, index)
-  until byte < 128 or byte >= 192
-  return index
-end
-
--- Moves to the end of the identified character.
-local function end_character(str, index)
-  local byte = string.byte(str, index + 1)
-  while byte and byte >= 128 and byte < 192 do
-    index = index + 1
-    byte = string.byte(str, index + 1)
-  end
-  return index
-end
-
--- Build off matching. For now, only support basic replacements, but capture
--- groupings should be doable. We can even have custom group replacements and
--- transformations and stuff in lua. Currently, this takes group replacements
--- as \1 - \9.
--- Should work on UTF-8 text.
-regex.gsub = function(pattern_string, str, replacement)
-  local pattern = type(pattern_string) == "table" and
-    pattern_string or regex.compile(pattern_string)
-  local result, indices = {}
-  local matches, replacements = {}, {}
-  local offset = 0
-  repeat
-    indices = { regex.cmatch(pattern, str, offset) }
-    if #indices > 0 then
-      table.insert(matches, indices)
-      local currentReplacement = replacement
-      if #indices > 2 then
-        for i = 1, (#indices/2 - 1) do
-          currentReplacement = string.gsub(
-            currentReplacement,
-            "\\" .. i,
-            str:sub(indices[i*2+1], end_character(str,indices[i*2+2]-1))
-          )
-        end
-      end
-      currentReplacement = string.gsub(currentReplacement, "\\%d", "")
-      table.insert(replacements, { indices[1], #currentReplacement+indices[1] })
-      if indices[1] > 1 then
-        table.insert(result, str:sub(offset, previous_character(str, indices[1])) .. currentReplacement)
-      else
-        table.insert(result, currentReplacement)
-      end
-      offset = indices[2]
-    end
-  until #indices == 0 or indices[1] == indices[2]
-  return table.concat(result) .. str:sub(offset), matches, replacements
-end
-