Initial version of "rebar shell" command

For now, this is just a proof of concept; would make sense to add a lot
of things, such as quick access to invoking rebar itself (with approproate 
code reloading), as well as an eunit-aware version so that tests could be 
run interactively.

ebin/rebar.app

@@ -35,6 +35,7 @@
               rebar_upgrade,
               rebar_utils,
               rebar_xref,
+              rebar_shell,
               getopt,
               mustache ]},
   {registered, []},
@@ -77,6 +78,7 @@
                                rebar_eunit,
                                rebar_escripter,
                                rebar_edoc,
+                               rebar_shell,
                                rebar_xref
                               ]},
 

src/rebar.erl

@@ -342,7 +342,8 @@ command_names() ->
     ["check-deps", "clean", "compile", "create", "create-app", "create-node",
      "ct", "delete-deps", "doc", "eunit", "generate", "generate-appups",
      "generate-upgrade", "get-deps", "help", "list-deps", "list-templates",
-     "update-deps", "overlay", "version", "xref"].
+     "update-deps", "overlay", "shell", "version", "xref"].
+
 
 unabbreviate_command_names([]) ->
     [];

src/rebar_shell.erl

@@ -0,0 +1,60 @@
+%% -*- erlang-indent-level: 4;indent-tabs-mode: nil -*-
+%% ex: ts=4 sw=4 et
+%% -------------------------------------------------------------------
+%%
+%% rebar: Erlang Build Tools
+%%
+%% Copyright (c) 2011 Trifork
+%%
+%% Permission is hereby granted, free of charge, to any person obtaining a copy
+%% of this software and associated documentation files (the "Software"), to deal
+%% in the Software without restriction, including without limitation the rights
+%% to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+%% copies of the Software, and to permit persons to whom the Software is
+%% furnished to do so, subject to the following conditions:
+%%
+%% The above copyright notice and this permission notice shall be included in
+%% all copies or substantial portions of the Software.
+%%
+%% THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+%% IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+%% FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+%% AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+%% LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+%% OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+%% THE SOFTWARE.
+%% -------------------------------------------------------------------
+
+-module(rebar_shell).
+-author("Kresten Krab Thorup <krab@trifork.com>").
+
+-include("rebar.hrl").
+
+-export([shell/2]).
+
+shell(_Config, _AppFile) ->
+
+    case is_deps_dir(rebar_utils:get_cwd()) of
+	false ->
+	    true = code:add_pathz(ebin_dir()),
+	    
+	    user_drv:start(),
+
+	    %% this call never returns (until user quits shell)
+	    shell:server(false, false);
+
+	true ->
+	    ok
+    end,
+    ok.
+
+ebin_dir() ->
+    filename:join(rebar_utils:get_cwd(), "ebin").
+
+is_deps_dir(Dir) ->
+    case lists:reverse(filename:split(Dir)) of
+	[_, "deps" | _] ->
+	    true;
+	_V ->
+	    false
+    end.