Buck: Allow to trigger Maven deployment even when nothing changed

Buck extensively uses caching and storing metadata in buck-out
directory, so that it's not possible per design to re-trigger the
execution of custom rule, without wiping out the whole buck-out
directory. See also the discussion on this issue: [1].

The implementation of Maven deployment as a custom build rule with
a side effect is wrong approach to start with. It was only done as a
workaround, because buck doesn't offer `install` or `publish` command
that must not be free of side effects like it's the case with `build`
command. Having side effects with `build` command breaks bucks model.

As workaround for now add standalone Python script, that re-uses Buck
api_{deploy|install} targets, resolves $(location <target>) macros and
executes the deployment by calling mvn.py utility directly:

  $ tools/maven/api.py {deploy,install}

Dry run mode is supported as well:

  $ tools/maven/api.py -n {deploy,install}

[1] https://github.com/facebook/buck/issues/342

Change-Id: I7fb86ad6967a1fa1e7ac842ba5e0e8cf0103b773

Documentation/dev-buck.txt

@@ -670,6 +670,30 @@ Watchman can either be de-installed or disabled. See
 link:#buck-daemon[Using Buck daemon] section above how to temporarily
 disable `buckd`.
 
+=== Re-triggering rule execution
+
+There is no way to re-trigger custom rules with side effects, like
+`api_{deploy|install}`. This is a `genrule()` that depends on Java sources
+and is deploying the Plugin API through custom Python script to the local or
+remote Maven repositories. When for some reasons the deployment was undone,
+there is no supported way to re-trigger the execution of `api_{deploy|install}`
+targets. That's because `--no-cache` option will ignore the `Buck` cache, but
+there is no way to ignore `buck-out` directory. To overcome this Buck's design
+limitation new `tools/maven/api.py` script was added, that always re-triggers
+installation or deployment of Plugin API to local or Central Maven repository.
+
+```
+  tools/maven/api.py {deploy|install}
+```
+
+Dry run mode is also supported:
+
+```
+  tools/maven/api.py -n {deploy|install}
+```
+
+With this script the deployment would re-trigger on every invocation.
+
 == Troubleshooting Buck
 
 In some cases problems with Buck itself need to be investigated. See for example

tools/maven/api.py

@@ -0,0 +1,78 @@
+#!/usr/bin/env python
+# Copyright (C) 2015 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import print_function
+from argparse import ArgumentParser
+from json import loads
+from os import environ, path, remove
+from subprocess import check_call, check_output, Popen, PIPE
+from sys import stderr
+from tempfile import mkstemp
+
+
+def locations():
+  d = Popen('buck audit dependencies api'.split(),
+            stdin=None, stdout=PIPE, stderr=PIPE)
+  t = Popen('xargs buck targets --show_output'.split(),
+            stdin=d.stdout, stdout=PIPE, stderr=PIPE)
+  out = t.communicate()[0]
+  d.wait()
+  targets = []
+  outs = []
+  for e in out.strip().split('\n'):
+    t, o = e.split()
+    targets.append(t)
+    outs.append(o)
+  return dict(zip(targets, outs))
+
+parser = ArgumentParser()
+parser.add_argument('-n', '--dryrun', action='store_true')
+parser.add_argument('-v', '--verbose', action='store_true')
+
+subparsers = parser.add_subparsers(help='action', dest='action')
+subparsers.add_parser('deploy', help='Deploy to Maven (remote)')
+subparsers.add_parser('install', help='Install to Maven (local)')
+
+args = parser.parse_args()
+
+root = path.abspath(__file__)
+while not path.exists(path.join(root, '.buckconfig')):
+  root = path.dirname(root)
+
+if not args.dryrun:
+  check_call('buck build api'.split())
+target = check_output(('buck targets --json api_%s' % args.action).split())
+
+s = loads(target)[0]['cmd']
+
+fd, tempfile = mkstemp()
+s = s.replace('$(exe //tools/maven:mvn)', path.join(root, 'tools/maven/mvn.py'))
+s = s.replace('-o $OUT', '-o %s' % tempfile)
+
+locations = locations()
+
+while '$(location' in s:
+  start = s.index('$(location')
+  end = s.index(')', start)
+  target = s[start+11:end]
+  s = s.replace(s[start:end+1], locations[target])
+
+try:
+  if args.verbose or args.dryrun or environ.get('VERBOSE'):
+    print(s, file=stderr)
+  if not args.dryrun:
+    check_call(s.split())
+finally:
+  remove(tempfile)