pl.lapp: Support end-of-argument-list marker "--"

[ghost]

It would be great of pl.lapp could support the end-of-argument-list marker --.

Let's take this example.lua:

#!/usr/bin/lua
local lapp = require "pl.lapp"
local args = lapp[[
Example application
  <input> (file-in default stdin) The input file
  <output> (file-out default stdout) The output file
]]
print(args[1])

I would expect to be able to call example.lua and see following output:

# ./example.lua -- some argument list
some

Instead I get following error:

# ./example.lua -- some argument list
example: unrecognized parameter: -

Example application
  <input> (file-in default stdin) The input file
  <output> (file-out default stdout) The output file

I cannot call example.lua without such -- marker, because that makes pl.lapp open some and argument as input and output files:

# ./example.lua some argument list
example: some: No such file or directory

[ghost]

Minimally invasive patch against Penlight 1.2.1 that makes this work:

--- /usr/share/lua/5.2/pl/lapp.lua      2013-09-01 01:39:16.000000000 +0200
+++ pl/lapp.lua 2016-04-07 17:18:04.719756774 +0200
@@ -304,6 +304,7 @@
     local iextra = 1
     local i = 1
     local parm,ps,val
+    local end_of_flags = false

     local function check_parm (parm)
         local eqi = parm:find '='
@@ -321,8 +322,20 @@
     while i <= #arg do
         local theArg = arg[i]
         local res = {}
+        if theArg == "--" then
+            end_of_flags = true
+            iparm = #parmlist + 1
+
+            i = i + 1
+            theArg = arg[i]
+
+            if not theArg then
+                break
+            end
+        end
+
         -- look for a flag, -<short flags> or --<long flag>
-        if match('--$S{long}',theArg,res) or match('-$S{short}',theArg,res) then
+        if not end_of_flags and (match('--$S{long}',theArg,res) or match('-$S{short}',theArg,res)) then
             if res.long then -- long option
                 parm = check_parm(res.long)
             elseif #res.short == 1 or is_flag(res.short) then

[ghost]

The patch misbehaved if -- was the last argument. I fixed that by inserting following block:

--          theArg = arg[i]

            if not theArg then
                break
            end