Add pre and post script support for all commands

This change makes it possible to assign pre/post scripts to all
rebar commands. This allows users fine grained control over
when scripts and/or shell commands should be executed, where such
extensions are absolutely needed.

Several examples have been added to the rebar.config.sample file.

inttest/thooks/fish.erl

@@ -0,0 +1,5 @@
+-module(fish).
+
+-compile(export_all).
+
+fish() -> fish.

inttest/thooks/rebar.config

@@ -0,0 +1,7 @@
+%% pre-scripts
+{pre_hooks, [{clean, "echo preclean >> preclean.out"},
+             {compile, "echo precompile >> precompile.out"}]}.
+
+%% post-scripts
+{post_hooks, [{clean, "echo postclean >> postclean.out"},
+              {compile, "echo postcompile >> postcompile.out"}]}.

inttest/thooks/thooks_rt.erl

@@ -0,0 +1,40 @@
+-module(thooks_rt).
+
+-include_lib("eunit/include/eunit.hrl").
+-compile(export_all).
+
+files() ->
+    [
+     %% dummy lfe files
+     {copy, "../../rebar", "rebar"},
+     {copy, "rebar.config", "rebar.config"},
+     {copy, "fish.erl", "src/fish.erl"},
+     {create, "ebin/fish.app", app(fish, [fish])}
+    ].
+
+run(_Dir) ->
+    ?assertMatch({ok, _}, retest_sh:run("./rebar -v clean compile", [])),
+    ensure_command_ran_only_once("preclean"),
+    ensure_command_ran_only_once("precompile"),
+    ensure_command_ran_only_once("postclean"),
+    ensure_command_ran_only_once("postcompile"),
+    ok.
+
+ensure_command_ran_only_once(Command) ->
+    File = Command ++ ".out",
+    ?assert(filelib:is_regular(File)),
+    %% ensure that this command only ran once (not for each module)
+    {ok, Content} = file:read_file(File),
+    ?assertEqual(Command ++ "\n", binary_to_list(Content)).
+
+%%
+%% Generate the contents of a simple .app file
+%%
+app(Name, Modules) ->
+    App = {application, Name,
+           [{description, atom_to_list(Name)},
+            {vsn, "1"},
+            {modules, Modules},
+            {registered, []},
+            {applications, [kernel, stdlib]}]},
+    io_lib:format("~p.\n", [App]).

rebar.config.sample

@@ -138,3 +138,12 @@
 
 %% Subdirectories?
 {sub_dirs, ["dir1", "dir2"]}.
+
+%% == Pre/Post Command Hooks ==
+
+{pre_hooks, [{clean, "./prepare_package_files.sh"},
+             {compile, "escript generate_headers"}]}.
+
+{post_hooks, [{clean, "touch file1.out"},
+              {eunit, "touch file2.out"},
+              {compile, "touch postcompile.out"}]}.

src/rebar_core.erl

@@ -235,9 +235,11 @@ execute(Command, Modules, Config, ModuleFile) ->
             erlang:put(operations, erlang:get(operations) + 1),
 
             %% Run the available modules
+            apply_hooks(pre_hooks, Config, Command),
             case catch(run_modules(TargetModules, Command,
                                    Config, ModuleFile)) of
                 ok ->
+                    apply_hooks(post_hooks, Config, Command),
                     ok;
                 {error, failed} ->
                     ?FAIL;
@@ -302,6 +304,20 @@ run_modules([Module | Rest], Command, Config, File) ->
             {Module, Error}
     end.
 
+apply_hooks(Mode, Config, Command) ->
+    case rebar_config:get_local(Config, Mode, []) of
+        [] ->
+            skip;
+        Hooks when is_list(Hooks) ->
+            lists:foreach(fun apply_hook/1,
+                          [{Command, Hook} || Hook <- Hooks])
+    end.
+
+apply_hook({Command, {Command, Hook}}) ->
+    Msg = lists:flatten(io_lib:format("Command [~p] failed!~n", [Command])),
+    rebar_utils:sh(Hook, [{abort_on_error, Msg}]);
+apply_hook({Command, {HookCmd, _}}) when Command =/= HookCmd ->
+    skip.
 
 acc_modules(Modules, Command, Config, File) ->
     acc_modules(select_modules(Modules, Command, []),