Ensure filename are store relative to project directory

data/core/common.lua

@@ -238,4 +238,32 @@ function common.normalize_path(filename)
 end
 
 
+local function split_on_slash(s, sep_pattern)
+  local t = {}
+  for fragment in string.gmatch(s, "([^/\\]+)") do
+    t[#t + 1] = fragment
+  end
+  return t
+end
+
+
+function common.relative_path(ref_dir, dir)
+  local ref_ls = split_on_slash(ref_dir)
+  local dir_ls = split_on_slash(dir)
+  local i = 1
+  while i <= #ref_ls do
+    if dir_ls[i] ~= ref_ls[i] then
+      break
+    end
+    i = i + 1
+  end
+  local ups = ""
+  for k = i, #ref_ls do
+    ups = ups .. "../"
+  end
+  local rel_path = ups .. table.concat(dir_ls, "/", i)
+  return rel_path ~= "" and rel_path or "."
+end
+
+
 return common