docs/git_cookbook.md - chromium/src - Git at Google

 # Git Cookbook

 A collection of git recipes to do common git tasks.

 See also [Git Tips](git_tips.md).

 [TOC]

 ## Introduction

 This is designed to be a cookbook for common command sequences/tasks relating to
 git, git-cl, and how they work with Chromium development. It might be a little
 light on explanations.

 If you are new to git, or do not have much experience with a distributed version
 control system, you should also check out
 [The Git Community Book](http://book.git-scm.com/) for an overview of basic git
 concepts and general git usage. Knowing what git means by branches, commits,
 reverts, and resets (as opposed to what SVN means by them) will help make the
 following much more understandable.

 ## Chromium-specific Git Extensions

 Chromium ships a large number of git extensions in depot_tools. Some (like
 `git cl`) are required for the Chromium development workflow, while others
 (like `git map-branches`) are simple utilities to make your life easier.
 Please take a look at the full
 [depot_tools tutorial](https://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/depot_tools_tutorial.html),
 and at the extensive
 [man pages](https://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/depot_tools.html)
 for all the extensions.

 ## Excluding file(s) from git-cl, while preserving them for later use

 Since git-cl assumes that the diff between your current branch and its tracking
 branch is what should be used for the CL, the goal is to remove the unwanted
 files from the current branch, and preserve them in another branch.

 ### Method #1: Reset your current branch, and selectively commit files

 1.  `git log`  See the list of your commits. Find the hash of the last commit
      before your changes.
 1.  `git reset --soft abcdef` where abcdef is the hash found in the step above.
 1.  `git commit <files_for_this_cl> -m "files to upload"` commit the files you
      want included in the CL here.
 1.  `git new-branch new_branch_name` Create a new branch for the
     files that you want to exclude.
 1.  `git commit -a -m "preserved files"` Commit the rest of the files.

 ### Method #2: Create a new branch, reset, then commit files to preserve

 This method creates a new branch from your current one to preserve your changes.
 The commits on the new branch are undone, and then only the files you want to
 preserve are recommitted.

 1.  `git checkout -b new_branch_name` This preserves your old files.
 1.  `git log` See the list of your commits. Find the hash of the last commit
     before your changes.
 1.  `git reset --soft abcdef` Where abcdef is the hash found in the step above.
 1.  `git commit <files_to_preserve> -m "preserved files"` Commit the found files
     into the `new_branch_name`.

 Then revert your files however you'd like in your old branch. The files listed
 in step 4 will be saved in `new_branch_name`

 ### Method #3: Cherry-pick changes into review branches

 If you are systematic in creating separate local commits for independent
 changes, you can make a number of different changes in the same client and then
 cherry-pick each one into a separate review branch.

 1.  Make and commit a set of independent changes.
 1.  `git log`  # see the hashes for each of your commits.
 1.  repeat checkout, cherry-pick, upload steps for each change 1..n
     1.  `git new-branch review-changeN` Create a new review branch
         tracking origin
     1.  `git cherry-pick <hash of change N>`
     1.  `git cl upload`

 If a change needs updating due to review comments, you can go back to your main
 working branch, update the commit, and re-cherry-pick it into the review branch.

 1.  `git checkout <working branch>`
 1.  Make changes.
 1.  If the commit you want to update is the most recent one:
     1.  `git commit --amend <files>`
 1.  If not:
     1.  `git commit <files>`
     1.  `git rebase -i origin`  # use interactive rebase to squash the new
         commit into the old one.
 1.  `git log`  # observe new hash for the change
 1.  `git checkout review-changeN`
 1.  `git reset --hard`  # remove the previous version of the change
 1.  `git cherry-pick <new hash of change N>`
 1.  `git cl upload`

 ## Sharing code between multiple machines

 Assume Windows computer named vista, and a Linux one named penguin.
 Prerequisite: both machines have git clones of the main git tree.

 ```shell
 vista$ git remote add linux ssh://penguin/path/to/git/repo
 vista$ git fetch linux
 vista$ git branch -a   # should show "linux/branchname"
 vista$ git checkout -b foobar linux/foobar
 vista$ hack hack hack; git commit -a
 vista$ git push linux  # push branch back to linux
 penguin$ git reset --hard  # update with new stuff in branch
 ```

 Note that, by default, `gclient sync` will update all remotes. If your other
 machine (i.e., `penguin` in the above example) is not always available,
 `gclient sync` will timeout and fail trying to reach it. To fix this, you may
 exclude your machine from being fetched by default:

     vista$ git config --bool remote.linux.skipDefaultUpdate true

 ## Reverting commits

 The command `git revert X` patches in the inverse of a particular commit.
 Using this command is one way of making a revert:

 ```shell
 git checkout origin   # start with trunk
 git revert abcdef
 git cl upload
 ```

 ## Retrieving, or diffing against an old file revision

 Git works in terms of commits, not files. Thus, working with the history of a
 single file requires modified version of the show and diff commands.

 ```shell
 # Find the commit you want in the file's commit log.
 git log path/to/file
 # This prints out the file contents at commit 123abc.
 git show 123abc:path/to/file
 # Diff the current version against path/to/file against the version at
 # path/to/file
 git diff 123abc -- path/to/file
 ```

 When invoking `git show` or `git diff`, the `path/to/file` is **not relative the
 the current directory**. It must be the full path from the directory where the
 .git directory lives. This is different from invoking `git log` which
 understands relative paths.

 ## Reusing a Git mirror

 If you have a nearby copy of a Git repo, you can quickly bootstrap your copy
 from that one then adjust it to point it at the real upstream one.

 1.  Clone a nearby copy of the code you want: `git clone coworker-machine:/path/to/repo`
 1.  Change the URL your copy fetches from to point at the real git repo:
     `git remote set-url origin https://chromium.googlesource.com/chromium/src.git`
 1.  Update your copy: `git fetch`
 1.  Delete any extra branches that you picked up in the initial clone:
     `git prune origin`
	# Git Cookbook

	A collection of git recipes to do common git tasks.

	See also [Git Tips](git_tips.md).

	[TOC]

	## Introduction

	This is designed to be a cookbook for common command sequences/tasks relating to
	git, git-cl, and how they work with Chromium development. It might be a little
	light on explanations.

	If you are new to git, or do not have much experience with a distributed version
	control system, you should also check out
	[The Git Community Book](http://book.git-scm.com/) for an overview of basic git
	concepts and general git usage. Knowing what git means by branches, commits,
	reverts, and resets (as opposed to what SVN means by them) will help make the
	following much more understandable.

	## Chromium-specific Git Extensions

	Chromium ships a large number of git extensions in depot_tools. Some (like
	`git cl`) are required for the Chromium development workflow, while others
	(like `git map-branches`) are simple utilities to make your life easier.
	Please take a look at the full
	[depot_tools tutorial](https://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/depot_tools_tutorial.html),
	and at the extensive
	[man pages](https://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/depot_tools.html)
	for all the extensions.

	## Excluding file(s) from git-cl, while preserving them for later use

	Since git-cl assumes that the diff between your current branch and its tracking
	branch is what should be used for the CL, the goal is to remove the unwanted
	files from the current branch, and preserve them in another branch.

	### Method #1: Reset your current branch, and selectively commit files

	1. `git log` See the list of your commits. Find the hash of the last commit
	before your changes.
	1. `git reset --soft abcdef` where abcdef is the hash found in the step above.
	1. `git commit <files_for_this_cl> -m "files to upload"` commit the files you
	want included in the CL here.
	1. `git new-branch new_branch_name` Create a new branch for the
	files that you want to exclude.
	1. `git commit -a -m "preserved files"` Commit the rest of the files.

	### Method #2: Create a new branch, reset, then commit files to preserve

	This method creates a new branch from your current one to preserve your changes.
	The commits on the new branch are undone, and then only the files you want to
	preserve are recommitted.

	1. `git checkout -b new_branch_name` This preserves your old files.
	1. `git log` See the list of your commits. Find the hash of the last commit
	before your changes.
	1. `git reset --soft abcdef` Where abcdef is the hash found in the step above.
	1. `git commit <files_to_preserve> -m "preserved files"` Commit the found files
	into the `new_branch_name`.

	Then revert your files however you'd like in your old branch. The files listed
	in step 4 will be saved in `new_branch_name`

	### Method #3: Cherry-pick changes into review branches

	If you are systematic in creating separate local commits for independent
	changes, you can make a number of different changes in the same client and then
	cherry-pick each one into a separate review branch.

	1. Make and commit a set of independent changes.
	1. `git log` # see the hashes for each of your commits.
	1. repeat checkout, cherry-pick, upload steps for each change 1..n
	1. `git new-branch review-changeN` Create a new review branch
	tracking origin
	1. `git cherry-pick <hash of change N>`
	1. `git cl upload`

	If a change needs updating due to review comments, you can go back to your main
	working branch, update the commit, and re-cherry-pick it into the review branch.

	1. `git checkout <working branch>`
	1. Make changes.
	1. If the commit you want to update is the most recent one:
	1. `git commit --amend <files>`
	1. If not:
	1. `git commit <files>`
	1. `git rebase -i origin` # use interactive rebase to squash the new
	commit into the old one.
	1. `git log` # observe new hash for the change
	1. `git checkout review-changeN`
	1. `git reset --hard` # remove the previous version of the change
	1. `git cherry-pick <new hash of change N>`
	1. `git cl upload`

	## Sharing code between multiple machines

	Assume Windows computer named vista, and a Linux one named penguin.
	Prerequisite: both machines have git clones of the main git tree.

	```shell
	vista$ git remote add linux ssh://penguin/path/to/git/repo
	vista$ git fetch linux
	vista$ git branch -a # should show "linux/branchname"
	vista$ git checkout -b foobar linux/foobar
	vista$ hack hack hack; git commit -a
	vista$ git push linux # push branch back to linux
	penguin$ git reset --hard # update with new stuff in branch
	```

	Note that, by default, `gclient sync` will update all remotes. If your other
	machine (i.e., `penguin` in the above example) is not always available,
	`gclient sync` will timeout and fail trying to reach it. To fix this, you may
	exclude your machine from being fetched by default:

	vista$ git config --bool remote.linux.skipDefaultUpdate true

	## Reverting commits

	The command `git revert X` patches in the inverse of a particular commit.
	Using this command is one way of making a revert:

	```shell
	git checkout origin # start with trunk
	git revert abcdef
	git cl upload
	```

	## Retrieving, or diffing against an old file revision

	Git works in terms of commits, not files. Thus, working with the history of a
	single file requires modified version of the show and diff commands.

	```shell
	# Find the commit you want in the file's commit log.
	git log path/to/file
	# This prints out the file contents at commit 123abc.
	git show 123abc:path/to/file
	# Diff the current version against path/to/file against the version at
	# path/to/file
	git diff 123abc -- path/to/file
	```

	When invoking `git show` or `git diff`, the `path/to/file` is **not relative the
	the current directory**. It must be the full path from the directory where the
	.git directory lives. This is different from invoking `git log` which
	understands relative paths.

	## Reusing a Git mirror

	If you have a nearby copy of a Git repo, you can quickly bootstrap your copy
	from that one then adjust it to point it at the real upstream one.

	1. Clone a nearby copy of the code you want: `git clone coworker-machine:/path/to/repo`
	1. Change the URL your copy fetches from to point at the real git repo:
	`git remote set-url origin https://chromium.googlesource.com/chromium/src.git`
	1. Update your copy: `git fetch`
	1. Delete any extra branches that you picked up in the initial clone:
	`git prune origin`