Auto find tryserver master for git cl try

git_cl.py

Index: git_cl.py
diff --git a/git_cl.py b/git_cl.py
index 77f4a9e9f13c769e02e6acdadb087acb64f05224..398751cf64ecb52e72c7e3b1f3e1826d235a7265 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -2231,10 +2231,10 @@ def CMDtry(parser, args):
       "-b", "--bot", action="append",
       help=("IMPORTANT: specify ONE builder per --bot flag. Use it multiple "
             "times to specify multiple builders. ex: "
-            "'-bwin_rel:ui_tests,webkit_unit_tests -bwin_layout'. See "
+            "'-b win_rel:ui_tests,webkit_unit_tests -b win_layout'. See "
             "the try server waterfall for the builders name and the tests "
             "available. Can also be used to specify gtest_filter, e.g. "
-            "-bwin_rel:base_unittests:ValuesTest.*Value"))
+            "-b win_rel:base_unittests:ValuesTest.*Value"))
   group.add_option(
       "-m", "--master", default='',
       help=("Specify a try master where to run the tries."))
@@ -2276,8 +2276,45 @@ def CMDtry(parser, args):
     options.name = cl.GetBranch()
 
   if options.bot and not options.master:
-    parser.error('For manually specified bots please also specify the '
-                 'tryserver master, e.g. "-m tryserver.chromium.linux".')
+    err_msg = ''
+    map_url = 'http://builders-map.appspot.com/'

[Paweł Hajdan Jr., 2014/08/08 11:13:50]

This should use HTTPS.

[sheyang, 2014/08/11 19:30:06]

Done.

+    try:
+      res = urllib2.urlopen(map_url)
+      master_map = json.load(res)
+    except urllib2.URLError as url_e:
+      err_msg = ('Fail to fetch builder-to-master map from %s. Error: %s.' %

[Paweł Hajdan Jr., 2014/08/08 11:13:50]

nit: Fail -> Failed

[sheyang, 2014/08/11 19:30:05]

Done.

+                 (map_url, url_e))
+      logging.warn(err_msg)

[Paweł Hajdan Jr., 2014/08/08 11:13:50]

Why do we need this (here and below) if we actually record the error and print
it using parser.error?

[sheyang, 2014/08/11 19:30:05]

Removed.

+    except ValueError as val_e:
+      err_msg = 'Invalid json string from %s. Error: %s.' % (map_url, val_e)
+      logging.warn(err_msg)
+
+    if master_map:

[Paweł Hajdan Jr., 2014/08/08 11:13:50]

Have you tested the code path when we catch an exception? This seems likely to
throw NameError: name 'master_map' is not defined

I'd recommend initializing master_map to none above.

[sheyang, 2014/08/11 19:30:05]

Done.

+      for bot in options.bot:
+        if ':' in bot:
+          builder, _ = bot.split(':', 1)
+        else:
+          builder = bot
+        master_list = master_map.get(builder, [])
+        if not master_list:
+          err_msg = 'Cannot find a master for builder %s.' % builder
+          break
+        elif len(master_list) > 1:
+          err_msg = ('The builder name %s exists in multiple masters %s.' %
+                     (builder, master_list))
+          break
+        else:
+          cur_master = master_list[0]
+          if not options.master:
+            options.master = cur_master
+          elif options.master != cur_master:
+            err_msg = 'The builders do not belong to the same master.'
+            break
+
+    if err_msg:
+      parser.error('Tryserver master cannot be found because: %s\n'
+                   'Please manually specify the tryserver master'
+                   ', e.g. "-m tryserver.chromium.linux".' % err_msg)
 
   def GetMasterMap():
     # Process --bot and --testfilter.