Simplify war rule

Current implementation makes assumption for the location of context
content artifacts: one sub directory level. This is not future
proof as migration to built in gwt_binary() has shown.

Move from inducing the location to use of Buck's own $(location)
macro and provide the paramter to pack_war.py through cmd rather
than srcs.

Change-Id: I69037920e21963a62c8edd6edc296d72c7454e5a

war.bucklet

diff --git a/war.bucklet b/war.bucklet
index 0394375..0ac346a 100644
--- a/war.bucklet
+++ b/war.bucklet
@@ -20,7 +20,8 @@
 #   name = 'gitiles',
 #   libs = ['//gitiles-servlet:servlet'],
 #   context = [
-#     ':recourses.zip',
+#     '//gitiles-servlet:static-resources',
+#     ':web_xml',
 #   ],
 #   visibility = ['PUBLIC']
 # )
@@ -38,27 +39,15 @@
   for l in pgmlibs:
     cmd.extend(['--pgmlib', l])
 
-  src = []
   dep = []
   if context:
-    root = get_base_path()
-    if root:
-      root = '/'.join(['..' for _ in root.split('/')]) + '/'
-    for r in context:
-      dep.append(r[:r.rindex('.')])
-      if r.startswith('//'):
-        r = root + r[2:]
-        r = r.replace(':', '/')
-      elif r.startswith(':'):
-        r = r[1:]
-      src.append(genfile(r))
-  if src:
-    cmd.append('$SRCS')
+    for t in context:
+      dep.append(t)
+      cmd.append('$(location %s)' % t)
 
   genrule(
     name = name,
     cmd = ' '.join(cmd),
-    srcs = src,
     deps = libs + pgmlibs + dep + ['//bucklets/tools:pack_war'],
     out = name + '.war',
     visibility = visibility,