Include range summary when rolling into chromium.

tools/release/chromium_roll.py

Index: tools/release/chromium_roll.py
diff --git a/tools/release/chromium_roll.py b/tools/release/chromium_roll.py
index b7a31661ef14ea20a0ff66c3760dd9c6a7704556..8a3ff4a0a7c8695dc1ff43a50cbb13a27669780d 100755
--- a/tools/release/chromium_roll.py
+++ b/tools/release/chromium_roll.py
@@ -10,6 +10,10 @@ import sys
 from common_includes import *
 
 
+ROLL_SUMMARY = ("Summary of changes available at:\n"
+                "https://chromium.googlesource.com/v8/v8/+log/%s..%s")
+
+
 class Preparation(Step):
   MESSAGE = "Preparation."
 
@@ -27,6 +31,20 @@ class DetectLastPush(Step):
     self["push_title"] = self.GitLog(n=1, format="%s",
                                      git_hash=self["last_push"])
 
+    # The master revision this release is based on.
+    self["push_base"] = self.GetLatestReleaseBase()
+
+    # FIXME(machenbach): Manually specifying a revision doesn't work at the
+    # moment. Needs more complicated logic to find the correct push_base above.
+    # Maybe delete that parameter entirely?

[tandrii(chromium), 2015/02/13 22:29:08]

+1 for deleting it based on this rational, yet I don't know why it was added in
the first place. Was this expected to be specified by sheriffs who do new
release?

[Michael Achenbach, 2015/02/16 12:20:28]

Some weird historical stuff. Probably needed if a push went completely wrong.

+    assert not self._options.last_push
+
+    # Determine the master revision of the last roll.
+    version = self.GetVersionTag(self._options.last_roll)
+    assert version
+    self["last_rolled_base"] = self.GetLatestReleaseBase(version=version)
+    assert self["last_rolled_base"]
+
 
 class SwitchChromium(Step):
   MESSAGE = "Switch to Chromium checkout."
@@ -69,13 +87,17 @@ class UploadCL(Step):
         cwd=self._options.chromium) is None:
       self.Die("Failed to create deps for %s" % self["last_push"])
 
-    commit_title = "Update V8 to %s." % self["push_title"].lower()
-    sheriff = ""
+    message = []
+    message.append("Update V8 to %s." % self["push_title"].lower())
+
+    message.append(
+        ROLL_SUMMARY % (self["last_rolled_base"][:8], self["push_base"][:8]))

[tandrii(chromium), 2015/02/13 22:29:08]

8chars*4bits = 32 bits should be enough for everybody :P

[Michael Achenbach, 2015/02/16 12:20:28]

I actually ran a test once over our repo and found out that the normal git
summary size of 7 is not enough. There is an ambiguous commit. Therefore we need
8.

[tandrii(chromium), 2015/02/16 14:32:28]

So, I actually had some fun with this Birthday's paradox. At V8's current
commits number (~30k), there is 10% chance of a collision even with 8 chars!

============================================================
commits          probability of hash[:7] collission
   2324          0.010
   7522          0.100
  10000          0.170
  10946          0.200
  12429          0.250
  19291          0.500
  20000          0.525
  27282          0.750
  30000          0.813
  40000          0.949
  49723          0.990
  50000          0.991
============================================================
commits          probability of hash[:8] collission
   9292          0.010
  10000          0.012
  20000          0.045
  30000          0.099
  30085          0.100
  40000          0.170
  43782          0.200
  49712          0.250
  50000          0.253
============================================================

[Jakob Kummerow, 2015/02/16 19:54:55]

Just give it 12 chars or so (or 20, I don't care), to be reasonably safe for the
foreseeable future.

+
     if self["sheriff"]:
-      sheriff = ("\n\nPlease reply to the V8 sheriff %s in case of problems."
-                 % self["sheriff"])
-    self.GitCommit("%s%s\n\nTBR=%s" %
-                       (commit_title, sheriff, self._options.reviewer),
+      message.append("Please reply to the V8 sheriff %s in case of problems."
+          % self["sheriff"])
+    message.append("TBR=%s" % self._options.reviewer)
+    self.GitCommit("\n\n".join(message),
                    author=self._options.author,
                    cwd=self._options.chromium)
     if not self._options.dry_run:
@@ -119,6 +141,8 @@ class ChromiumRoll(ScriptsBase):
                               "directory to automate the V8 roll."))
     parser.add_argument("-l", "--last-push",
                         help="The git commit ID of the last candidates push.")
+    parser.add_argument("--last-roll", required=True,
+                        help="The git commit ID of the last rolled version.")
     parser.add_argument("--use-commit-queue",
                         help="Check the CQ bit on upload.",
                         default=False, action="store_true")