Copy Crashpad into the Chrome tree instead of importing it via DEPS

third_party/crashpad/README.chromium

 Name: Crashpad
 Short Name: crashpad
-URL: https://crashpad.googlecode.com/
+URL: https://crashpad.chromium.org/
 Version: unknown
-Revision: see DEPS
+Revision: 6bebb10829332dee5c7315abafb0a8bf32840c15
 License: Apache 2.0
 License File: crashpad/LICENSE
 Security Critical: yes
 
 Description:
 Crashpad is a crash-reporting system. It's the successor to Breakpad.
 
+Crashpad’s authoritative upstream repository is
+https://chromium.googlesource.com/crashpad/crashpad.
+
+Because Crashpad depends on some Chromium code (notably base and build), it is
+acceptable to make changes to this in-Chromium copy of Crashpad in order to
+conform to interface changes in Chromium. These changes must be noted in the
+“local modifications” section below, and should also be reflected in the
+authoritative Crashpad repository as soon as practical.
+
+Substantive development must occur in the authoritative Crashpad repository. If
+this type of work is done in the in-Chromium copy, it will be obliterated the
+next time Crashpad is imported into Chromium.
+
+To update the in-Chromium copy of Crashpad:
+
+git remote add crashpad https://chromium.googlesource.com/crashpad/crashpad
+git pull --strategy=subtree --squash crashpad master_or_hash

[Mark Mentovai, 2015/12/08 23:36:24]

I want to replace this sequence of steps with a script that also formats the
commit message nicely, updates the revision in this file, and maybe drops the
“local modifications” section if there are no diffs between upstream and the
import. But before I do that, I wanted to ask some questions about this process.

I had expected to tell the merge both the “from” and “to” commit-ishes from
Crashpad to merge into the current branch. This only has a “to”, and presumably
git does something to figure out where to start merging from. This is a little
more scary to me, since we won’t have merge commits to identify this
definitively to git. We do have the “revision” field in this file, and I was
hoping to use that. Do either of you know of a way to make this work?

The other bit of git magic is that the subtree merge magically finds
third_party/crashpad/crashpad without being told. That’s scary too, and I want
to tell it the path explicitly. I thought that “--strategy=recursive
-Xsubtree=third_party/crashpad/crashpad” would work, but it doesn’t. Ideas?

[scottmg, 2015/12/08 23:47:18]

Sorry, I don't know. If I was doing it, I have made the steps something like rm
-rf, cp -R, git add, git commit, as it's going to land as a squashed patch
anyway.

I would probably summon primiano@ as he seems to know a lot about all of git's
funny business.

[Mark Mentovai, 2015/12/09 01:35:26]

scottmg wrote:
I don’t want to trash local modifications that were made for base interface
changes if those haven’t had a chance to migrate back up to the authoritative
home, though. That’s why I went with a merge-based approach.
Good call, I sent out a cry for help.

[Robert Sesek, 2015/12/09 16:26:13]

Try looking at https://git-scm.com/docs/git-merge-base. It's generally for
three-way/octopus merges, but you can potentially use it to identify the
divergent point and make sure it matches the hash in the README. I don't think
there's a way to manually specify the mergebase (that's basically a rebase
--onto then, isn't it?).

[Primiano Tucci (use gerrit), 2015/12/09 16:48:49]

I had an internal thread with Mark and scott.
I think this cannot be just one git command. You need a script here.
by squashing (and you cannot do otherwise, you can't do merges in the chromium
repo) git does not have enough context on what CLs to merge.
It's really a ~10 lines bash script you want here.

copy-pasting from the internal thread with Mark:

To port a change chromium -> crashpad
In the chromium repo:
git format-patch -o /tmp/ -1 --binary $SHA1 --add-header="Message-Id: Merged
from chromium $SHA1" -- third_party/crashpad/ # (mind the trailing slash)
with SHA1 being the SHA1 of the change you want to port.

In the crashpad repo:
git am -m -3 -p3 /tmp/0001-whatever-name.patch
git cl upload

(I love how -1 in the format-patch command means "just export the 1st commit"
while -3 in am means "three way merge")

To sync-up changes crashpad -> chromium 
well here you need a script which just figures out the last thing you merged
from chromium and takes the rest.
Logically the script should do something like:
 - Find the last commit in the history of chromium -- third_party/crashpad/ that
was merged (use some annotation in the commit message)
 - from there you should get the SHA1 (in $true_crashpad_repo) of the last
crashpad CL merged
 - at this point you want to get the revlist of crashpad for all commits in the
range SHA1..HEAD excluding the chromium one (which have the "Merged from
chromium" annotation) and cherry-pick +squash them

Let me know if you need help on the latter (should be a short-ish bash script)

[Mark Mentovai, 2015/12/09 22:09:45]

After some discussion, this turned into the script at
https://codereview.chromium.org/1513843002/.

+git commit
+git remote remove crashpad
+
 Local Modifications:
-None.
+ - Cherry-pick upstream 7efdc94f5982a1f9654c53fd4bf5663e5efa66ce.