Bazel: Migrate workspace status script to python

This allows to seamlessly build Gerrit on different operating systems.
See also discussions in: [1], [2].

[1] https://github.com/bazelbuild/bazel/issues/5958
[2] https://github.com/bazelbuild/bazel/issues/10151

Change-Id: I7738a23c08f4890a2010182587b64a2979256ad4

.bazelrc

@@ -1,4 +1,4 @@
-build --workspace_status_command=./tools/workspace-status.sh --strategy=Closure=worker
+build --workspace_status_command="python ./tools/workspace_status.py" --strategy=Closure=worker
 build --repository_cache=~/.gerritcodereview/bazel-cache/repository
 build --action_env=PATH
 build --disk_cache=~/.gerritcodereview/bazel-cache/cas

tools/workspace-status.sh

@@ -1,21 +0,0 @@
-#!/usr/bin/env bash
-
-# This script will be run by bazel when the build process starts to
-# generate key-value information that represents the status of the
-# workspace. The output should be like
-#
-# KEY1 VALUE1
-# KEY2 VALUE2
-#
-# If the script exits with non-zero code, it's considered as a failure
-# and the output will be discarded.
-
-function rev() {
-  cd $1; git describe --always --match "v[0-9].*" --dirty
-}
-
-echo STABLE_BUILD_GERRIT_LABEL $(rev .)
-for p in plugins/* ; do
-  test -d "$p" || continue
-  echo STABLE_BUILD_$(echo $(basename $p)_LABEL|tr '[a-z]' '[A-Z]' ) $(rev $p)
-done

tools/workspace_status.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python
+
+# This script will be run by bazel when the build process starts to
+# generate key-value information that represents the status of the
+# workspace. The output should be like
+#
+# KEY1 VALUE1
+# KEY2 VALUE2
+#
+# If the script exits with non-zero code, it's considered as a failure
+# and the output will be discarded.
+
+from __future__ import print_function
+import os
+import subprocess
+import sys
+
+ROOT = os.path.abspath(__file__)
+while not os.path.exists(os.path.join(ROOT, 'WORKSPACE')):
+    ROOT = os.path.dirname(ROOT)
+CMD = ['git', 'describe', '--always', '--match', 'v[0-9].*', '--dirty']
+
+
+def revision(directory, parent):
+    try:
+        os.chdir(directory)
+        return subprocess.check_output(CMD).strip().decode("utf-8")
+    except OSError as err:
+        print('could not invoke git: %s' % err, file=sys.stderr)
+        sys.exit(1)
+    except subprocess.CalledProcessError as err:
+        print('error using git: %s' % err, file=sys.stderr)
+        sys.exit(1)
+    finally:
+        os.chdir(parent)
+
+
+print("STABLE_BUILD_GERRIT_LABEL %s" % revision(ROOT, ROOT))
+for d in os.listdir(os.path.join(ROOT, 'plugins')):
+    p = os.path.join('plugins', d)
+    if os.path.isdir(p):
+        v = revision(p, ROOT)
+        if v:
+            print('STABLE_BUILD_%s_LABEL %s' % (os.path.basename(p).upper(), v))