new feature: Keep line number

bin/moonc

@@ -21,7 +21,7 @@ local help = [[Usage: %s [options] files/directories...
     -l          Perform lint on the file instead of compiling
     -b          Dump parse and compile time (doesn't write output)
     -v          Print version
-
+    -n          Keep line numbers so that every output line maps a input line
     --          Read from standard in, print to standard out
                 (Must be first and only argument)
 ]]
@@ -248,6 +248,7 @@ else
 			benchmark = opts.b,
 			show_posmap = opts.X,
 			show_parse_tree = opts.T,
+			keep_line_number = opts.n
 		})
 
 		if not success then

moonscript/cmd/moonc.moon

@@ -60,6 +60,15 @@ gettime = do
     else
       nil, "LuaSocket needed for benchmark"
 
+
+import pos_to_line from require "moonscript.util"
+
+reverse_line_number = (code, line_table, line_num) ->
+  for i = line_num,0,-1
+    if line_table[i]
+      return pos_to_line code, line_table[i]
+  "unknown"
+
 -- compiles file to lua, returns lua code
 -- returns nil, error on error
 -- returns true if some option handled the output instead
@@ -107,6 +116,30 @@ compile_file_text = (text, opts={}) ->
     }, "\n"
     return true
 
+  if opts.keep_line_number
+    line_map = {}  -- lua line to moon line
+    for lua_line_number,moon_pos in pairs(posmap_or_err)
+      line_map[lua_line_number] = reverse_line_number text, posmap_or_err, lua_line_number
+    aligned_code = ""
+    lua_line_number = 1
+    current_moon_line_number = 1
+    for line in string.gmatch(code..'\n', "(.-)\n")
+      if moon_line_number = line_map[lua_line_number]
+        to_next_line = false
+        while current_moon_line_number < moon_line_number
+          to_next_line = true
+          aligned_code ..= '\n'
+          current_moon_line_number += 1
+        unless to_next_line
+          aligned_code ..= ' '  -- add a space
+      else
+        aligned_code ..= ' '
+        -- BUG cannot tell whether it is part of multi-line string
+        -- there should be \n only if it is a multi-line string
+      aligned_code ..= line
+      lua_line_number += 1
+    code = aligned_code .. '\n'
+
   code
 
 write_file = (fname, code) ->