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depot_tools_tutorial - A tutorial introduction to the Chromium depot_tools git extensions.
The Chromium depot_tools(7) suite contains many git workflow-enhancing tools which are designed to work together to enable anyone to wrangle the Chromium codebase expertly. This tutorial explains how to do development on Chromium using these tools. This will cover:
Setting up
Getting the code
TL;DR
Creating / Uploading a CL
Updating the code
Managing multiple CLs
Managing dependent CLs
Example Walkthrough
Please refer to the manpages (or --help
output) for details about any of the commands mentioned in this tutorial.
Note |
If your platform does not support manpages (or you prefer something a bit more expressive than plain text) you can find all documentation in html form in the[DEPOT_TOOLS]/man/html folder. |
This tutorial assumes basic familiarity with git terminology and concepts. If you need to brush up on these, the following are very good resources:
Think like (a) Git - A lighthearted overview of git. If you’re sorta-familiar with git, but not comfortable with it, then give this a look.
Git Immersion Tutorial - An in-depth git tutorial.
pcottle’s Visual Git Branching - An excellent interactive/graphical demo on how git handles commits, branches, and shows the operations git performs on them.
Pro Git book - “The” book for learning git from basics to advanced concepts. A bit dry, but very through.
If you’ve tried these out and are still having some trouble getting started, there are many other resources online which should help. If you’re really really stuck, then chat up one of the Chromium infrastructure team members for some pointers.
Litmus Test
If you know what git add
, git status
, git commit
do and you know essentially what git rebase
does, then you should know enough to follow along.
LINUX / MAC
Clone the depot_tools repository:
$ git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
Add depot_tools to the end of your PATH (you will probably want to put this in your ~/.bashrc
or ~/.zshrc
). Assuming you cloned depot_tools to /path/to/depot_tools
:
$ export PATH=$PATH:/path/to/depot_tools
WINDOWS
Download the depot_tools bundle and extract it somewhere.
Warning |
DO NOT use drag-n-drop or copy-n-paste extract from Explorer, this will not extract the hidden “.git” folder which is necessary for depot_tools to autoupdate itself. You can use “Extract all…” from the context menu though. |
Add depot_tools to the start of your PATH (must be ahead of any installs of Python). Assuming you unzipped the bundle to C:\workspace\depot_tools
:
With Administrator access:
Control Panel → System and Security → System → Advanced system settings
Modify the PATH system variable to include C:\workspace\depot_tools
.
Without Administrator access:
Control Panel → User Accounts → User Accounts → Change my environment variables
Add a PATH user variable: C:\workspace\depot_tools;%PATH%
.
From a cmd.exe
shell, run the command gclient
(without arguments). On first run, gclient will install all the Windows-specific bits needed to work with the code, including msysgit and python.
Note |
|
If you have never used git before, you’ll need to set some global git configurations; substitute your name and email address in the following commands:
$ git config --global user.name "John Doe"
$ git config --global user.email "[email protected]"
$ git config --global core.autocrlf false
$ git config --global core.filemode false
$ # and for fun!
$ git config --global color.ui true
$ # get the code
$ # In an empty directory:
$ fetch {chromium,...}
$ # Update third_party repos and run pre-compile hooks
$ gclient sync
$ # Make a new change and upload it for review
$ git new-branch
$ # repeat: [edit, git add, git commit]
$ git cl upload
$ # After change is reviewed, commit with the CQ
$ git cl set_commit
$ # Note that the committed hash which lands will /not/ match the
$ # commit hashes of your local branch.
Pick an empty directory and run one of the following:
$ fetch chromium # Basic checkout for desktop Chromium
$ fetch android # Chromium checkout for Android platform
$ fetch ios # Chromium checkout for iOS platform
When the fetch
tool completes you should have the following in your working directory:
.gclient # A configuration file for you source checkout
src/ # Top-level Chromium source checkout.
If you are on linux and fetching the code for the first time, then you’ll need to run:
$ cd src && ./build/install-build-deps.sh
And finally:
$ gclient sync
This will pull all dependencies of the Chromium src checkout. You will need to run this any time you update the main src checkout, including when you switch branches.
Note |
The remainder of the tutorial assumes that your current working directory is the src/ folder mentioned in Getting the code. |
Each CL corresponds exactly with a single branch in git. Any time you want to begin a new CL:
$ git new-branch
This will create and checkout a new branch named branch_name
which will track the default upstream branch (origin/master
). See git-new-branch(1) for more features.
Commit as many changes as you like to this branch. When you want to upload it for review, run:
$ git cl upload
This will take the diff of your branch against its upstream branch (in that case origin/master), and will post it to the Chromium code review site.
Inevitably, you’ll want to pull in changes from the main Chromium repo. This is pretty easy with depot_tools:
$ git rebase-update
This command will update all of your CLs to contain the latest code from their upstreams. It will also automatically clean up CLs which have been committed and a couple other nice things. See git-rebase-update(1) for the full scoop.
One thing to look out for are merge conflicts. These happen for exactly the same as they do with SVN, but the experience is a little more controllable with git. git rebase-update
will try to rebase all your branches for you, but if it encounters a merge conflict in one, it will halt and leave you in a rebase conflict state (see git-rebase(1)). Resolving git rebase
merge conflicts is beyond the scope of this tutorial, but there are many good sources online (see the Prerequisites for some).
Sometimes you’re pretty certain that you’ve committed a certain branch, but git rebase-update
isn’t able to tell that for sure. This is usually because your branch doesn’t rebase cleanly. You could just delete the branch with git branch -D
, but you’d like to double check the diff of your branch against its upstream before deleting it. If this is the case you can abort the rebase started by git rebase-update
, and then run git-squash-branch(1) to flatten your branch into a single commit. When you run git rebase-update
again, you’ll get a (hopefully) much smaller / saner diff. If it turns out you were wrong about your branch being fully committed, you can use git-reflog(1) to reset your branch back to where it was before. If the diff looks inconsequential, you can use git rebase --skip
to ignore it, and then git rebase-update
will clean it up for you.
Once you’re done resolving all of the merge conflict, just run git rebase-update
, and it will pick up where it left off. Once the command has finished updating all of your branches, it will return you back to the branch you started on.
Note |
Running git rebase-update will update all your branches, but it will not automatically run gclient sync to update your dependencies. |
Sometimes you want to work on more than one CL at once (say, you have a CL posted for review and want to work on something else). For each CL that you want to work on, just use git new-branch
.
Once you start to have more than one CL at a time, it can be easy to lose your bearings. Fortunately, depot_tools has two tools to help you out:
$ git map
* 7dcfe47 (frozen_changes) 2014-03-12 ~ FREEZE.unindexed
* 4b0c180 2014-03-12 ~ modfile
* 59a7cca 2014-03-12 ~ a deleted file
* 6bec695 (origin/master) 2014-03-11 ~ Add neat feature <(frozen_changes)
* d15a38a 2014-03-11 ~ Epic README update
* d559894 (master) 2014-03-11 ~ Important upstream change
| * 9c311fd (cool_feature) 2014-03-11 ~ Respond to CL comments
| | * 2a1eeb2 (subfeature) 2014-03-11 ~ integrate with CoolService
| | * d777af6 2014-03-11 ~ slick commenting action
| |/
| * 265803a 2014-03-11 ~ another improvement <(subfeature)
| * 6d831ac (spleen_tag) 2014-03-11 ~ Refactor spleen
| * 82e74ab 2014-03-11 ~ Add widget
|/
* d08c5b3 (bogus_noparent) 2014-03-11 ~ Wonderful beginnings <(cool_feature)
Note that this example repo is in dire need of a git-rebase-update(1)!
$ git map-branches
origin/master
cool_feature
subfeature
frozen_changes *
master
git-map(1)
This tool shows you the history of all of your branches in a pseudo-graphical format. In particular, it will show you which commits all of your branches are on, which commit you currently have checked out, and more. Check out the doc for the full details.
git-map-branches(1)
This tool just shows you which branches you have in your repo, and their upstream relationship to each other (as well as which branch you have checked out at the moment).
Additionally, sometimes you need to switch between branches, but you’ve got work in progress. You could use git-stash(1), but that can be tricky to manage because you need to remember which branches you stashed what changes on. Helpfully depot_tools includes two tools which can greatly assist in case:
git-freeze(1) allows you to put the current branch in 'suspended animation' by committing your changes to a specially-named commit on the top of your current branch. When you come back to your branch later, you can just run git-thaw(1) to get your work-in-progress changes back to what they were.
Another useful tool is git-rename-branch(1). Unlike git branch -m
, this tool will correctly preserve the upstream relationships of your branch compared to its downstreams.
Finally, take a look at git-upstream-diff(1). This will show you the combined diff for all the commits on your branch against the upstream tracking branch. This is exactly what git cl upload
will push up to code review. Additionally, consider trying the --wordwise
argument to get a colorized per-word diff (instead of a per-line diff).
Now that you know how to manage independent CLs, we’ll see how to manage dependent CLs. Dependent CLs are useful when your second (or third or fourth or …) CL depends on the changes in one of your other CLs (such as: CL 2 won’t compile without CL 1, but you want to submit them as two separate reviews).
Like all of the other CLs we’ve created, we use git-new-branch(1), but this time with an extra argument. First, git checkout
the branch you want to base the new one on (i.e. CL 1), and then run:
$ git new-branch --upstream_current
This will make a new branch which tracks the current branch as its upstream (as opposed to origin/master). All changes you commit to this branch will be in addition to the previous branch, but when you git cl upload
, you will only upload the diff for the dependent (child) branch. You may have as many branches nested in this fashion as you like.
git-map(1) and git-map-branches(1) are particularly helpful when you have dependent branches. In addition, there are two helper commands which let you traverse your working copy up and down this tree of branches: git-nav-upstream(1) and git-nav-downstream(1).
Sometimes when dealing with dependent CLs, it turns out that you accidentally based a branch on the wrong upstream, but since then you’ve committed changes to it, or even based anotherbranch off of that one. Or you discover that you have two independent CLs that would actually be much better off as dependent CLs. In instances like these, you can check out the offending branch and use git-reparent-branch(1) to move it to track a different parent. Note that this can also be used to move a branch from tracking origin/master
to lkgr
or vice versa.
This section will demo what a typical workflow looks like when writing, updating, and committing multiple CLs.
$ fetch chromium
... truncated output ...
$ cd src
(only on linux)
$ ./build/install-build-deps.sh
... truncated output ...
Pull in all dependencies for HEAD
$ gclient sync
... truncated output ...
Let's fix something!
$ git new-branch fix_typo
$ echo -e '/Banana\ns/Banana/Kuun\nwq' | ed build/whitespace_file.txt
1503
It was a Domo-Banana.
It was a Domo-Kuun.
1501
$ git commit -am 'Fix terrible typo.'
[fix_typo 615ffa7] Fix terrible typo.
1 file changed, 1 insertion(+), 1 deletion(-)
$ git map
* 615ffa7 (HEAD -> fix_typo) 2014-04-10 ~ Fix terrible typo.
* beec6f4 (origin/master, origin/HEAD) 2014-04-10 ~ Make ReflectorImpl use mailboxes <(fix_typo)
* 41290e0 2014-04-10 ~ don't use glibc-specific execinfo.h on uclibc builds
* a76fde7 2014-04-10 ~ [fsp] Add requestUnmount() method together with the request manager.
* 9de7a71 2014-04-10 ~ linux_aura: Use system configuration for middle clicking the titlebar.
* 073b0c2 2014-04-10 ~ ContentView->ContentViewCore in ContentViewRenderView
* 2250f53 2014-04-10 ~ ozone: evdev: Filter devices by path
* 33a7a74 2014-04-10 ~ Always output seccomp error messages to stderr
$ git status
# On branch fix_typo
# Your branch is ahead of 'origin/master' by 1 commit.
# (use "git push" to publish your local commits)
#
nothing to commit, working directory clean
$ git cl upload -r [email protected] --send-mail
... truncated output ...
While we wait for feedback, let's do something else.
$ git new-branch chap2
$ git map-branches
origin/master
chap2 *
fix_typo
$ cat >> build/whitespace_file.txt <..." to update what will be committed)
# (use "git checkout -- ..." to discard changes in working directory)
#
# modified: build/whitespace_file.txt
#
no changes added to commit (use "git add" and/or "git commit -a")
Someone on the code review pointed out that our typo-fix has a typo :( We're still working on 'chap2' but we really want to land 'fix_typo', so let's switch over and fix it.
$ git freeze
$ git checkout fix_typo
Switched to branch 'fix_typo'
Your branch is ahead of 'origin/master' by 1 commit.
(use "git push" to publish your local commits)
$ echo -e '/Kuun\ns/Kuun/Kun\nwq' | ed build/whitespace_file.txt
1501
It was a Domo-Kuun.
It was a Domo-Kun.
1500
$ git upstream-diff --wordwise
diff --git a/build/whitespace_file.txt b/build/whitespace_file.txt
index 3eba355..57cdcee 100644
--- a/build/whitespace_file.txt
+++ b/build/whitespace_file.txt
@@ -17,7 +17,7 @@ swept up the streets (for it is in London that our scene lies), rattling along
the housetops, and fiercely agitating the scanty flame of the lamps that
struggled against the elements. A hooded figure emerged.
It was a Domo-BananaKun.
"What took you so long?", inquired his wife.
$ git commit -am 'Fix typo for good!'
[fix_typo 2c0ad9c] Fix typo for good!
1 file changed, 1 insertion(+), 1 deletion(-)
$ git cl upload
... truncated output ...
Since we got lgtm, let the CQ land it.
$ git cl set_commit
$ git map
* 0e2e52e (chap2) 2014-04-10 ~ FREEZE.unindexed
| * 2c0ad9c (HEAD -> fix_typo) 2014-04-10 ~ Fix typo for good!
| * 615ffa7 2014-04-10 ~ Fix terrible typo.
|/
* beec6f4 (origin/master, origin/HEAD) 2014-04-10 ~ Make ReflectorImpl use mailboxes <(chap2, fix_typo)
* 41290e0 2014-04-10 ~ don't use glibc-specific execinfo.h on uclibc builds
* a76fde7 2014-04-10 ~ [fsp] Add requestUnmount() method together with the request manager.
* 9de7a71 2014-04-10 ~ linux_aura: Use system configuration for middle clicking the titlebar.
* 073b0c2 2014-04-10 ~ ContentView->ContentViewCore in ContentViewRenderView
* 2250f53 2014-04-10 ~ ozone: evdev: Filter devices by path
* 33a7a74 2014-04-10 ~ Always output seccomp error messages to stderr
Switch back to where we were using the nav* commands (for fun... git checkout would work here too)
$ git map-branches
origin/master
chap2
fix_typo *
$ git nav-upstream
Note: checking out 'origin/master'.
You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.
If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:
git checkout -b
HEAD is now at beec6f4... Make ReflectorImpl use mailboxes
$ git nav-downstream
Previous HEAD position was beec6f4... Make ReflectorImpl use mailboxes
Switched to branch 'chap2'
Your branch is ahead of 'origin/master' by 1 commit.
(use "git push" to publish your local commits)
Please select a downstream branch
0. chap2
1. fix_typo
Selection (0-1)[0]: 0
$ git map-branches
origin/master
chap2 *
fix_typo
Now we can pick up on chapter2 where we left off.
$ git thaw
$ git diff
diff --git a/build/whitespace_file.txt b/build/whitespace_file.txt
index 3eba355..9d08d9d 100644
--- a/build/whitespace_file.txt
+++ b/build/whitespace_file.txt
@@ -34,3 +34,7 @@ with his fork, watching the runny jelly spread and pool across his plate,
like the blood of a dying fawn. \"It reminds me of that time --\" he started, as
his wife cut in quickly: \"-- please. I can't bear to hear it.\". A flury of
images coming from the past flowed through his mind.
+
+"You recall what happened on Mulholland drive?" The ceiling fan rotated slowly
+overhead, barely disturbing the thick cigarette smoke. No doubt was left about
+when the fan was last cleaned.
$ cat >> build/whitespace_file.txt < chap2) 2014-04-10 ~ Finish chapter 2
| * 2c0ad9c (fix_typo) 2014-04-10 ~ Fix typo for good!
| * 615ffa7 2014-04-10 ~ Fix terrible typo.
|/
* beec6f4 (origin/master, origin/HEAD) 2014-04-10 ~ Make ReflectorImpl use mailboxes <(chap2, fix_typo)
* 41290e0 2014-04-10 ~ don't use glibc-specific execinfo.h on uclibc builds
* a76fde7 2014-04-10 ~ [fsp] Add requestUnmount() method together with the request manager.
* 9de7a71 2014-04-10 ~ linux_aura: Use system configuration for middle clicking the titlebar.
* 073b0c2 2014-04-10 ~ ContentView->ContentViewCore in ContentViewRenderView
* 2250f53 2014-04-10 ~ ozone: evdev: Filter devices by path
* 33a7a74 2014-04-10 ~ Always output seccomp error messages to stderr
$ git cl upload -r [email protected] --send-mail
... truncated output ...
We poke a committer until they lgtm :)
$ git cl set_commit
While that runs through the CQ, let's get started on chapter 3. Since we know that chapter 3 depends on chapter 2, we'll track the current chapter2 branch.
$ git new-branch --upstream_current chap3
$ cat >> build/whitespace_file.txt < chap3) 2014-04-10 ~ beginning of chapter 3
* ceef712 (chap2) 2014-04-10 ~ Finish chapter 2 <(chap3)
| * 2c0ad9c (fix_typo) 2014-04-10 ~ Fix typo for good!
| * 615ffa7 2014-04-10 ~ Fix terrible typo.
|/
* beec6f4 (origin/master, origin/HEAD) 2014-04-10 ~ Make ReflectorImpl use mailboxes <(chap2, fix_typo)
* 41290e0 2014-04-10 ~ don't use glibc-specific execinfo.h on uclibc builds
* a76fde7 2014-04-10 ~ [fsp] Add requestUnmount() method together with the request manager.
* 9de7a71 2014-04-10 ~ linux_aura: Use system configuration for middle clicking the titlebar.
* 073b0c2 2014-04-10 ~ ContentView->ContentViewCore in ContentViewRenderView
* 2250f53 2014-04-10 ~ ozone: evdev: Filter devices by path
* 33a7a74 2014-04-10 ~ Always output seccomp error messages to stderr
We haven't updated the code in a while, so let's do that now.
$ git rebase-update
Fetching origin
From https://upstream
beec6f4..59cdb73 master -> origin/master
Rebasing: chap2
Rebasing: fix_typo
Failed! Attempting to squash fix_typo ... Success!
Rebasing: chap3
Reparented chap3 to track origin/master (was tracking chap2)
Deleted branch fix_typo (was 5d26fec).
Deleted branch chap2 (was 5d26fec).
Well look at that. The CQ landed our typo and chapter2 branches already and git rebase-update cleaned them up for us.
$ gclient sync
... truncated output ...
$ git map
* 93fe917 (HEAD -> chap3) 2014-04-10 ~ beginning of chapter 3
* 5d26fec (origin/master, origin/HEAD) 2014-04-10 ~ Finish chapter 2 <(chap3)
* df7fefb 2014-04-10 ~ Revert 255617, due to it not tracking use of the link doctor page properly.
* 4b39cda 2014-04-10 ~ Fix terrible typo.
* 248c5b6 2014-04-10 ~ Temporarily CHECK(trial) in ChromeRenderProcessObserver::OnSetFieldTrialGroup.
* 8171df8 2014-04-10 ~ Remove AMD family check for the flapper crypto accelerator.
* d6a30d2 2014-04-10 ~ Change the Pica load benchmark to listen for the polymer-ready event
* beec6f4 2014-04-10 ~ Make ReflectorImpl use mailboxes
* 41290e0 2014-04-10 ~ don't use glibc-specific execinfo.h on uclibc builds
* a76fde7 2014-04-10 ~ [fsp] Add requestUnmount() method together with the request manager.
* 9de7a71 2014-04-10 ~ linux_aura: Use system configuration for middle clicking the titlebar.
* 073b0c2 2014-04-10 ~ ContentView->ContentViewCore in ContentViewRenderView
* 2250f53 2014-04-10 ~ ozone: evdev: Filter devices by path
* 33a7a74 2014-04-10 ~ Always output seccomp error messages to stderr
Someone on IRC mentions that they actually landed a chapter 3 already! We should pull their changes before continuing. Brace for a code conflict!
$ git rebase-update
Fetching origin
From https://upstream
5d26fec..59cdb73 master -> origin/master
Rebasing: chap2
... lots of output, it's a conflict alright :(...
$ git diff
diff --cc build/whitespace_file.txt
index 1293282,f903ea2..0000000
--- a/build/whitespace_file.txt
+++ b/build/whitespace_file.txt
@@@ -42,4 -42,5 +42,9 @@@ when the fan was last cleaned
There was an poignant pause.
CHAPTER 3:
++<<<<<<< 59cdb7335b1c3a159ecc22214441cbe2194de25c
+Hilariousness! This chapter is awesome!
++=======
+ Mr. Usagi felt that something wasn't right. Shortly after the Domo-Kun left he
+ began feeling sick.
++>>>>>>> beginning of chapter 3
Oh, well, that's not too bad. In fact... that's a terrible chapter 3!
$ $EDITOR build/whitespace_file.txt
... /me deletes bad chapter 3 ...
$ git add build/whitespace_file.txt
$ git diff --cached
diff --git a/build/whitespace_file.txt b/build/whitespace_file.txt
index 1293282..f903ea2 100644
--- a/build/whitespace_file.txt
+++ b/build/whitespace_file.txt
@@ -42,4 +42,5 @@ when the fan was last cleaned.
There was an poignant pause.
CHAPTER 3:
-Hilariousness! This chapter is awesome!
+Mr. Usagi felt that something wasn't right. Shortly after the Domo-Kun left he
+began feeling sick.
Much better
$ git rebase --continue
Applying: beginning of chapter 3
$ git rebase-update
Fetching origin
chap3 up-to-date
$ gclient sync
... truncated output ...
$ git map
* 1cb4f5b (HEAD -> chap3) 2014-04-10 ~ beginning of chapter 3
* 59cdb73 (origin/master, origin/HEAD) 2014-04-10 ~ Refactor data interchange format. <(chap3)
* 34676a3 2014-04-10 ~ Ensure FS is exited for all not-in-same-page navigations.
* 7d4784e 2014-04-10 ~ Add best chapter2 ever!
* 5d26fec 2014-04-10 ~ Finish chapter 2
* df7fefb 2014-04-10 ~ Revert 255617, due to it not tracking use of the link doctor page properly.
* 4b39cda 2014-04-10 ~ Fix terrible typo.
* 248c5b6 2014-04-10 ~ Temporarily CHECK(trial) in ChromeRenderProcessObserver::OnSetFieldTrialGroup.
* 8171df8 2014-04-10 ~ Remove AMD family check for the flapper crypto accelerator.
* d6a30d2 2014-04-10 ~ Change the Pica load benchmark to listen for the polymer-ready event
* beec6f4 2014-04-10 ~ Make ReflectorImpl use mailboxes
* 41290e0 2014-04-10 ~ don't use glibc-specific execinfo.h on uclibc builds
* a76fde7 2014-04-10 ~ [fsp] Add requestUnmount() method together with the request manager.
* 9de7a71 2014-04-10 ~ linux_aura: Use system configuration for middle clicking the titlebar.
* 073b0c2 2014-04-10 ~ ContentView->ContentViewCore in ContentViewRenderView
* 2250f53 2014-04-10 ~ ozone: evdev: Filter devices by path
* 33a7a74 2014-04-10 ~ Always output seccomp error messages to stderr
$ git cl upload
... truncated output ...
So there you have the basic flow. Note that you don’t have to do chromium development using these tools. Any git workflow is compatible, as long as git cl upload
is able to upload good patches.
Hopefully that gives you a good starting overview on Chromium development using depot_tools. If you have questions which weren’t answered by this tutorial or the man pages for the tools (see the index of all tools here: depot_tools(7)), please feel free to ask.
CL
A change-list. This is a diff which you would like to commit to the codebase.
DEPS
A file in the chromium checkout which gclient sync
uses to determine what dependencies to pull in. This file also contains hooks.
LKGR
Last Known Good Revision. This is a git-tag(1) which tracks the last version of origin/master
which has passed the full set of testing on the main Chromium waterfall.
Part of the chromium depot_tools(7) suite. These tools are meant to assist with the development of chromium and related projects. Download the tools from here.