Returning empty result instead of nil.

[bbense]

The problem seems to be that the new :matching option causes the code to return one empty array before it returns a nil at the end of the search. I did add the necessary e dir after checking out the
code from github. The problem appears whether you use the matching code or not.

iex -S mix
Erlang/OTP 17 [erts-6.2] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Interactive Elixir (1.0.2) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> {:ok, walker} = DirWalker.start_link("test/dir", matching: ~r(a|f))
{:ok, #PID<0.79.0>}
iex(2)> file = DirWalker.next(walker)
["test/dir/a.txt"]
iex(3)> file = DirWalker.next(walker)
["test/dir/c/d/f.txt"]
iex(4)> file = DirWalker.next(walker)
[]
iex(5)> file = DirWalker.next(walker)
nil
iex(6)> {:ok, walker} = DirWalker.start_link("test/dir")
{:ok, #PID<0.85.0>}
iex(7)> file = DirWalker.next(walker)
["test/dir/a.txt"]
iex(8)> file = DirWalker.next(walker)
["test/dir/b.txt"]
iex(9)> file = DirWalker.next(walker)
["test/dir/c/d/f.txt"]
iex(10)> file = DirWalker.next(walker)
[]
iex(11)> file = DirWalker.next(walker)
nil

[bbense]

If you use a count larger than the default of one it works just fine.

iex(7)> {:ok, walker} = DirWalker.start_link("test/dir")
{:ok, #PID<0.86.0>}
iex(8)> files = DirWalker.next(walker,2)
["test/dir/b.txt", "test/dir/a.txt"]
iex(9)> files = DirWalker.next(walker,2)
["test/dir/c/d/f.txt"]
iex(10)> files = DirWalker.next(walker,2)
nil

[bbense]

I found the problem, since the matching function can return an empty list w/o processing a list, the call handler needs to check for returning { [] , [] } and instead set the result to nil if returning two empty arrays.

iex -S mix
Erlang/OTP 17 [erts-6.2] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Compiled lib/dir_walker.ex
Generated dir_walker.app
Interactive Elixir (1.0.2) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> {:ok, walker} = DirWalker.start_link("test/dir")
{:ok, #PID<0.116.0>}
iex(2)> file = DirWalker.next(walker)

20:20:18.903 [debug] Handling test/dir/a.txt

20:20:18.906 [debug] Replying with ["test/dir/a.txt"] ["test/dir/b.txt", ["test/dir/badlink", "test/dir/c", "test/dir/goodlink"]]
["test/dir/a.txt"]
iex(3)> file = DirWalker.next(walker)

20:20:27.541 [debug] Handling test/dir/b.txt

20:20:27.541 [debug] Replying with ["test/dir/b.txt"] ["test/dir/badlink", ["test/dir/c", "test/dir/goodlink"]]
["test/dir/b.txt"]
iex(4)> file = DirWalker.next(walker)

20:20:33.013 [info] Dangling symlink found: test/dir/badlink

20:20:33.013 [debug] Handling test/dir/badlink

20:20:33.013 [debug] Replying with ["test/dir/badlink"] ["test/dir/c", ["test/dir/goodlink"]]
["test/dir/badlink"]
iex(5)> file = DirWalker.next(walker)

20:20:37.798 [debug] Handling test/dir/c/d/f.txt

20:20:37.798 [debug] Replying with ["test/dir/c/d/f.txt"] ["test/dir/goodlink"]
["test/dir/c/d/f.txt"]
iex(6)> file = DirWalker.next(walker)

20:20:42.461 [debug] Handling test/dir/goodlink

20:20:42.461 [debug] Replying with ["test/dir/goodlink"] []
["test/dir/goodlink"]
iex(7)> file = DirWalker.next(walker)
nil
iex(8)> {:ok, walker} = DirWalker.start_link("test/dir", matching: ~r(b) )
{:ok, #PID<0.124.0>}
iex(9)> file = DirWalker.next(walker)

20:21:57.695 [debug] Handling test/dir/a.txt

20:21:57.695 [debug] Moving on to rest [["test/dir/b.txt", "test/dir/badlink", "test/dir/c", "test/dir/goodlink"]]

20:21:57.695 [debug] Handling test/dir/b.txt

20:21:57.695 [debug] Replying with ["test/dir/b.txt"] ["test/dir/badlink", ["test/dir/c", "test/dir/goodlink"]]
["test/dir/b.txt"]
iex(10)> file = DirWalker.next(walker)

20:22:04.351 [info] Dangling symlink found: test/dir/badlink

20:22:04.351 [debug] Handling test/dir/badlink

20:22:04.351 [debug] Replying with ["test/dir/badlink"] ["test/dir/c", ["test/dir/goodlink"]]
["test/dir/badlink"]
iex(11)> file = DirWalker.next(walker)

20:22:07.887 [debug] Handling test/dir/c/d/f.txt

20:22:07.887 [debug] Moving on to rest [["test/dir/goodlink"]]

20:22:07.888 [debug] Handling test/dir/goodlink

20:22:07.888 [debug] Moving on to rest []

20:22:07.888 [debug] Replying with [] []
[]

The Logger debug statements are in my current version. The fix was to add this to the main handle_call routine.

def handle_call({:get_next, n}, _from, {path_list, mappers}) do
{result, new_path_list} = first_n(path_list, n, mappers, _result=[])
Logger.debug("Replying with #{inspect(result)} #{inspect(new_path_list)}")
if( {result, new_path_list} == { [] , [] }) do
result = nil
end
{ :reply, result, {new_path_list, mappers} }
end