tryserver recipe_module: Add get_tags.

recipe_modules/tryserver/api.py

Index: recipe_modules/tryserver/api.py
diff --git a/recipe_modules/tryserver/api.py b/recipe_modules/tryserver/api.py
index 8bd8df87f94bdfb68e7ad7f91ee0a15f54fec61a..dced07a0b8926f5b519de0461e393d5e79a26dbc 100644
--- a/recipe_modules/tryserver/api.py
+++ b/recipe_modules/tryserver/api.py
@@ -2,6 +2,7 @@
 # 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
 
@@ -245,3 +246,42 @@ class TryserverApi(recipe_api.RecipeApi):
           failure_hash.hexdigest()
 
       raise
+
+  def get_tags(self, patch_text=None):

[tandrii(chromium), 2016/04/26 10:29:58]

get_tags is confusing because 1) tag has different meaning git 2) there is
already subproject_tag here, which seems unrelated.

I think get_footers is better.

[martiniss, 2016/04/29 21:34:40]

good point, changed.

+    """Retrieves tags from the patch description.
+
+    tags are lines with a format like
+    FOO=arbitrary bar here
+    It's used to annotate a CL with some machine readable data; for example, you
+    can set BUG=123123 to tell bugdroid to update a bug when you close this CL.

[tandrii(chromium), 2016/04/26 10:29:58]

iannucci@ gave us awesome footers support in depot_tools (git_footers.py). IMO,
we should be transitioning to proper git footers  instead of k=v stuff. That
said, k=v is reality, so this code deserves to exist. Still, I'd probably prefer
a tool inside depot_tools, maybe in that git_footers.py that would extra all
footers.

[iannucci, 2016/04/26 23:50:56]

Yes, if we can use the footers format, that would be best. The K=V format is
pretty ad hoc and gets messed up by various processes.

That said, CQ currently does crap like:
  
  Review URL: https://codereview.chromium.org/1897903002

In order to use footers-style, we need to change CQ to use footers style and not
break existing footers on the review message first.

The reason that footers are better than k=v is that gerrit (and some of our
tools, like gnumbd) have code to natively understand/manipulate them. It would
be conceivable to add indexing support for them e.g. in gerrit, whereas it would
never be feasible to add support for them for k=v (since there's basically no
format restrictions for k=v stuff, so it's not possible to reliably pluck them
out of the commit message).

[tandrii(chromium), 2016/04/27 13:06:13]

Fix: https://chromereviews.googleplex.com/412857013

[martiniss, 2016/04/29 21:34:40]

Ok, i'm switching to this style. Updating code appropriately.

+    """
+    if not patch_text:
+      cmd = [self.m.depot_tools.git_cl_path, 'description']
+
+      codereview = None
+      if not self.can_apply_issue:
+        raise recipe_api.StepFailure("Cannot get tags from gerrit yet.")

[tandrii(chromium), 2016/04/26 10:29:58]

tbh, i don't understand why this doens't work for gerrit. git cl desc works.

[martiniss, 2016/04/29 21:34:40]

It does, but I don't know how to generate the URL that I need to pass it. For
rietveld, we have that information, but I don't understand which properties to
look at.

I tried looking at clank for inspiration, and they only care about
event.patchSet.ref, and the url, so I can't use that I think.

Tandrii, do you know the magic incantation of properties I should use?

+      else:
+        codereview = 'rietveld'
+        url = (
+            self.m.properties['rietveld'].strip('/') + '/' +
+            str(self.m.properties['issue']))
+
+      cmd.extend([url, '-d', codereview])
+      patch_text = self.m.step('Get description', cmd).stdout

[tandrii(chromium), 2016/04/26 10:29:58]

i'd add separate "get_cl_description" api with just this step.

[iannucci, 2016/04/26 23:50:56]

git_cl.description, but yes +1

[martiniss, 2016/04/29 21:34:40]

Done.

+
+    tags = collections.defaultdict(list)
+    for line in patch_text.splitlines():
+      split = line.split('=', 1)
+      if len(split) == 1:
+        continue
+
+      name, contents = split
+      tags[name.upper()].append(contents)
+
+    return tags
+
+  def get_tag(self, tag, patch_text=None):
+    """Gets a specific tag from a CL description"""
+    return self.get_tags(patch_text).get(tag, [])
+