Add post upload hook to substitute hashtags for their mapped text

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index ae5a2183162c81026e8e382e6792b75fe362cc8c..3403651780eacc416d8dc67bf45ec4e6a7e47de7 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -9,6 +9,7 @@ See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
 
+import csv
 import fnmatch
 import os
 import re
@@ -362,6 +363,24 @@ def PostUploadHook(cl, change, output_api):
                 'Trybots do not yet work for non-master branches. '
                 'Automatically added \'NOTRY=true\' to the CL\'s description'))
 
+    # Read and process the HASHTAGS file.
+    with open('HASHTAGS', 'rb') as hashtags_csv:
+      hashtags_reader = csv.reader(hashtags_csv, delimiter=',')
+      for row in hashtags_reader:
+        if not row or row[0].startswith('#'):
+          # Ignore empty lines and comments
+          continue
+        hashtag = row[0]
+        mapped_text = row[1]
+        # Search for the hashtag in the description.
+        if re.search('#%s' % hashtag, new_description, re.M | re.I):
+          # Add the mapped text if it does not already exist in the description.
+          if not re.search(r'^%s$' % mapped_text, new_description, re.M | re.I):
+            new_description += '\n%s' % mapped_text
+            results.append(
+                output_api.PresubmitNotifyResult(
+                    'Found \'#%s\', automatically added \'%s\' to the CL\'s '
+                    'description' % (hashtag, mapped_text)))
 
     # If the description has changed update it.
     if new_description != original_description: