Make PropEr a soft dependency

This prevents applications that depend on Jiffy from requiring PropEr as
a dependency just to run Jiffy's full test suite. If you want to run the
full test suite you'll have to run Jiffy's Makefile directly which
creates a `.jiffy.dev` marker that enables the full test suite.

.gitignore

@@ -1,3 +1,4 @@
+.jiffy.dev
 *.app
 *.beam
 *.o

Makefile

@@ -15,11 +15,13 @@ distclean: clean
 	git clean -fxd
 
 
-depends:
+devmarker:
+	touch .jiffy.dev
+
+
+depends: devmarker
 	@if test ! -d ./deps; then \
 		$(REBAR) get-deps; \
-	else \
-		$(REBAR) update-deps; \
 	fi
 
 

rebar.config

@@ -1,7 +1,3 @@
-{deps, [
-    {proper, ".*", {git, "git://github.com/manopapad/proper.git", "master"}}
-]}.
-
 {port_specs, [{"priv/jiffy.so", ["c_src/*.c"]}]}.
 
 {port_env, [

rebar.config.script

@@ -0,0 +1,26 @@
+% This file is part of Jiffy released under the MIT license.
+% See the LICENSE file for more information.
+
+% Only include PropEr as a dependency when the JIFFY_DEV
+% environment variable is defined. This allows downstream
+% applications to avoid requiring PropEr.
+%
+% This script is based on the example provided with Rebar.
+
+ErlOpts = {erl_opts, [
+    {d, 'JIFFY_DEV'}
+]},
+
+Deps = {deps, [
+    {proper, ".*", {git, "git://github.com/manopapad/proper.git", "master"}}
+]},
+
+ConfigPath = filename:dirname(SCRIPT),
+DevMarker = filename:join([ConfigPath, ".jiffy.dev"]),
+
+case filelib:is_file(DevMarker) of
+    true ->
+        CONFIG ++ [ErlOpts, Deps];
+    false ->
+        CONFIG
+end.

test/jiffy_tests.erl

@@ -3,6 +3,8 @@
 
 -module(jiffy_tests).
 
+-ifdef(JIFFY_DEV).
+
 -include_lib("proper/include/proper.hrl").
 -include_lib("eunit/include/eunit.hrl").
 
@@ -130,3 +132,4 @@ escaped_char() ->
         end
     ).
 
+-endif.