For plugins, run 'git describe' from their BUCK directory

Thereby, we allow plugins to provide more than just one plugin (e.g.:
as javamelody does), and we get correct 'git describe' output when
cloning plugins under different names or more than once.

Change-Id: I7afe621265b3424ef78271e3bbeeca22b2cf4cf8

tools/default.defs

@@ -20,6 +20,8 @@ include_defs('//tools/java_doc.defs')
 include_defs('//tools/java_sources.defs')
 include_defs('//tools/git.defs')
 import copy
+import traceback
+import os
 
 # Set defaults on java rules:
 #  - Add AutoValue annotation processing support.
@@ -131,7 +133,10 @@ def gerrit_plugin(
     type = 'plugin',
     visibility = ['PUBLIC']):
   from multiprocessing import cpu_count
-  mf_cmd = 'v=%s;' % git_describe(name)
+  tb = traceback.extract_stack()
+  calling_BUCK_file = tb[-2][0]
+  calling_BUCK_dir = os.path.abspath(os.path.dirname(calling_BUCK_file))
+  mf_cmd = 'v=%s;' % git_describe(calling_BUCK_dir)
   if manifest_file:
     mf_src = [manifest_file]
     mf_cmd += 'sed "s:@VERSION@:$v:g" $SRCS >$OUT'

tools/git.defs

@@ -12,13 +12,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-def git_describe(plugin = None):
+def git_describe(directory = None):
   import subprocess
   cmd = ['git', 'describe', '--always', '--match', 'v[0-9].*', '--dirty']
-  if not plugin or plugin == '${pluginName}':
+  if not directory:
     p = subprocess.Popen(cmd, stdout = subprocess.PIPE)
   else:
-    p = subprocess.Popen(cmd, stdout = subprocess.PIPE, cwd = 'plugins/%s' % plugin)
+    p = subprocess.Popen(cmd, stdout = subprocess.PIPE, cwd = directory)
   v = p.communicate()[0].strip()
   r = p.returncode
   if r != 0: