tryserver recipe_module: Add get_tags.

recipe_modules/tryserver/api.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import collections
 import contextlib
 import hashlib
 
 from recipe_engine import recipe_api
 
 
 PATCH_STORAGE_RIETVELD = 'rietveld'
 PATCH_STORAGE_GIT = 'git'
 PATCH_STORAGE_SVN = 'svn'
 
@@ skipping 223 matching lines @@
       self.add_failure_reason(e.reason)
 
       failure_hash = hashlib.sha1()
       failure_hash.update(self.m.json.dumps(self._failure_reasons))
 
       step_result = self.m.step.active_result
       step_result.presentation.properties['failure_hash'] = \
           failure_hash.hexdigest()
 
       raise
+
+  def get_footers(self, patch_text=None):
+    """Retrieves footers from the patch description.
+
+    footers are lines with a format like
+    Foo:arbitrary bar here
+    These are  used to annotate a CL with some machine readable data.

[iannucci, 2016/05/12 00:25:52]

This description is not accurate. Footers are extracted from the last paragraph
of the text, as long as every line in that last paragraph has the form of
`^\w+(-(\w+))*:\s+.*$`. If any line in the last paragraph does not have this
format, the last paragraph is ignored and the text is considered to have no
footers.

[martiniss, 2016/05/13 19:23:56]

Ok, changed. I just moved to use git-footers, and said to look at those docs if
you want more info.

+    """
+    if not patch_text:
+      codereview = None
+      if not self.can_apply_issue: #pragma: no cover
+        raise recipe_api.StepFailure("Cannot get tags from gerrit yet.")
+      else:
+        codereview = 'rietveld'
+        patch = (
+            self.m.properties['rietveld'].strip('/') + '/' +
+            str(self.m.properties['issue']))
+
+      patch_text = self.m.git_cl.get_description(
+          patch=patch, codereview=codereview).stdout
+
+    tags = collections.defaultdict(list)
+    for line in patch_text.splitlines():
+      split = line.split(':', 1)
+      if len(split) == 1:
+        continue
+
+      name, contents = split
+      tags[name].append(contents)
+
+    return tags

[iannucci, 2016/05/12 00:25:52]

wait... why not use `git-footers` for this? If necessary, git footers should be
modified to accept text on stdin and write parsed footers to a json file. Don't
re-invent this parser.

[martiniss, 2016/05/13 19:23:56]

Done.

+
+  def get_footer(self, tag, patch_text=None):
+    """Gets a specific tag from a CL description"""
+    return self.get_footers(patch_text).get(tag, [])
+