bazel: generate the workspace version from the volatile status.

This generates a version file that looks correct, but doesn't rebuild
correctly.  Correct rebuilds will be provided by a version of
bazel containing

  a2897bff4c

Change-Id: I5101d7f2643d464cf32c8281a28ec6c3fc4fa2cf

.bazelrc

@@ -1 +1 @@
-build --strategy=Javac=worker
+build --workspace_status_command=./tools/workspace-status.sh --strategy=Javac=worker

BUILD

@@ -1,11 +1,10 @@
-load('//tools/bzl:genrule2.bzl', 'genrule2')
 load('//tools/bzl:pkg_war.bzl', 'pkg_war')
 
-genrule2(
-  name = 'version',
-  srcs = ['VERSION'],
-  cmd = "grep GERRIT_VERSION $< | cut -d \"'\" -f 2 >$@",
-  out = 'version.txt',
+genrule(
+  name = 'gen_version',
+  stamp = 1,
+  cmd = "grep STABLE_BUILD_GERRIT_LABEL < bazel-out/volatile-status.txt | cut -d ' ' -f 2 > $@",
+  outs = ['version.txt'],
   visibility = ['//visibility:public'],
 )
 

gerrit-war/BUILD

@@ -62,9 +62,9 @@ genrule2(
   cmd = ' && '.join([
     'cd $$TMP',
     'mkdir -p com/google/gerrit/common',
-    'cat $$ROOT/$(location //:version) >com/google/gerrit/common/Version',
+    'cat $$ROOT/$(location //:version.txt) >com/google/gerrit/common/Version',
     'zip -9Dqr $$ROOT/$@ .',
   ]),
-  tools = ['//:version'],
+  tools = ['//:version.txt'],
   out = 'gen_version.jar',
 )

tools/workspace-status.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+
+# 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.
+
+git_rev=$(git describe --always --match "v[0-9].*" --dirty)
+
+echo "STABLE_BUILD_GERRIT_LABEL ${git_rev}"