wiki:DeveloperGuidelines/Git

Version 78 (modified by Pat Tressel, 11 years ago) ( diff )

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Git

Table of Contents

  1. Developer Workflow
    1. Fork the Sahana Eden Repository
    2. Ongoing Coding
      1. Resolving Merge Conflicts
      2. Rebasing after pushing to GitHub
      3. Undoing a commit
    3. Working with multiple branches
    4. Creating a second working directory and repository
    5. Using Patches
    6. Story Branches
  2. Developer Configuration
    1. Windows
    2. Developer Tools
    3. Notifications
  3. Resources
  4. History
    1. Why?
    2. How?
      1. Migrating existing Branches

Sahana Eden uses the Git DVCS & hosts active branches on ​GitHub

Developer Workflow

Fork the Sahana Eden Repository

If you've not used GitHub before:

  1. Sign-up for an account on ​GitHub
  2. Set up git on you your computer by following ​these instructions.
    Note: In order to contribute code back to the Eden project, you need to "push" your changes to GitHub, and GitHub requires you to authenticate for that. The instructions describe authenticating using a password. If you don't want to do do that, you can use SSH keys instead, but the ​SSH setup is longer, and they do not provide instructions for Windows. If you're using Windows, you can follow ​these instructions. They're for Launchpad, not GitHub. The only difference is, while you're doing Step 5 (which has you copy the "OpenSSH" formatted public key to the clipboard), go over to the GitHub instructions, to the "Add your SSH key to GitHub" section. Ignore the Linux commands and do the part that saves your public key in your GitHub account. If you want, you can also save that public key in a file.
  3. There is ​on-line help at GitHub

Then get your own copy of the Eden repository (repo) on both GitHub and your local machine:

  1. Fork the Eden repo at: ​https://github.com/flavour/eden/fork
  2. Use git to clone your own new fork down to your PC, as follows: 
    cd web2py/applications
git clone git@github.com:mygitusername/eden.git
cd eden
git remote add upstream git://github.com/flavour/eden.git

https://docs.google.com/drawings/pub
​https://docs.google.com/drawings/d/1TppJKr9Qrq6I2KpkljRixx5gYh1seRqCXk8KDWdeIF0/edit

Ongoing Coding

cd web2py/applications/eden

# Update your local repository with latest code from the trunk repository on GitHub
git pull --rebase upstream

# Write Code

# Quick review of code (no test code left in, etc)
git diff

# Check for any new files which need adding
git status
git add .

# Commit Code (Note, no pushes to GitHub here)
git commit -am "My Story: Part 1"
.
.
.
git commit -am "My Story: Part N"

# Pull in changes from trunk
git pull --rebase upstream

# Resolve any conflicts (see below for how)

# Commit fixed code
git add .
git commit -a

# Review commits
git log

# Use rebase to squash commits to as few as possible to keep revision history clean & make it easier to review the work
# http://gitready.com/advanced/2009/02/10/squashing-commits-with-rebase.html
git rebase -i HEAD~N # Where N = Number of commits 

# Push to your branch on GitHub
git push

https://docs.google.com/drawings/pub
​https://docs.google.com/drawings/d/1KElPNMq_annNSi_2f5r9grD-c0c_aZh1KBAOqSAtuPA/edit

Once you have pushed to your branch on GitHub, you will likely want this to be merged with Trunk - this should be done via a Pull Request. This is done on GitHub:

https://docs.google.com/drawings/pub
​https://docs.google.com/drawings/d/1QmGeuQvFpg3pDQpM9xu81V7MlVy4uU8EzVIRqQ14MwU/edit

Resolving Merge Conflicts

If you encounter conflicts during the rebase, the conflicts will be tagged in the files with: 

<<<<<<< HEAD
# Commits from Trunk
=======
# Commits from <mystory>
>>>>>>> "My Story"

You can correct these conflict in your code text editor, then add them andcontinue the rebase: 

git add -u
git rebase --continue

You can create the .THIS & .OTHER files using: 

git show :2:file.txt > file.txt.THIS
git show :3:file.txt > file.txt.OTHER

You can use the changes to a file in the remote branch (theirs / OTHER): 

git checkout --theirs filename.c
git add filename.c
git commit

...or the changes to a file in your local branch (ours / THIS): 

git checkout --ours filename.c
git add filename.c
git commit

...or the changes to ALL files in the remote branch (theirs / OTHER): 

git checkout --theirs . # checkout our local version of all files
git add -u             # mark all conflicted files as merged
git commit             # commit the merge

Or the changes to ALL files in your local branch (ours / THIS) 

git checkout --ours . # checkout our local version of all files
git add -u            # mark all conflicted files as merged
git commit            # commit the merge

Although on Windows this seems by default to produce UTF-16 files! ('UCS-2 Little Endian'). A script to make this process easier for Windows users is attached: merge.cmd

Rebasing after pushing to GitHub

Squash your commits if they are not in between two executions of git pull or git merge: 

# Stash your current work
git stash
# N = number of commits to squash
git reset HEAD@{N}
git add -A
git commit -am 'Your commit message for the one-big-commit'
# Push to your branch on GitHub, overwriting any previous code there
git push origin +master
# Restore your work in-progress
git stash pop

Undoing a commit

You may need to remove a commit you've made, either if you find you don't want it, or if it needs to be fixed. (Note if your commit has already been pushed to GitHub and accepted into the trunk, then you should use a new commit to take out unwanted changes. This section only applies if you're fixing up your repository before the changes are in trunk.)

If you want to fix up your latest commit, you can undo the commit, and unstage the files in it, by doing: 

git reset HEAD~1

This will return your repository to its state before the git add commands that staged the files. Your changes will be in your working directory. HEAD~1 refers to the commit below the current tip of the branch.

If you want to uncommit N commits, but keep the code changes in your working directory: 

git reset HEAD~N

If you want to get rid of your latest commit, and do not want to keep the code changes, you can do a "hard" reset. 

git reset --hard HEAD~1

Likewise, if you want to discard the last N commits, and do not want to keep the code changes: 

git reset --hard HEAD~N

If you are not entirely sure you want to discard the code changes, but need a branch without them, you can simply check out a new branch that ends at the last commit you want. E.g. to make a branch that ends N commits before the latest: 

git checkout -b <new_branch_name> HEAD~N

See below for more on using multiple branches. To remove a commit from your repository on GitHub, use either the hard reset or new branch method above to reset your local repository to the commit you want on GitHub. GitHub will not let you overwrite a branch with a different history unless you tell it to with the --force option. If your local and remote branches have the same names, you only need to specify the branch name once, without the ":". 

git push --force origin <local_branch_name>:<github_branch_name>

Working with multiple branches

If you are working on several tasks, or want to make temporary changes for experimentation, or want to back up your work before doing a rebase or reset, you can do that by having multiple branches in your repository and switching between them. Each branch is a sequence of commits leading up to a specific head commit (which can be referred to as HEAD without confusion since git knows which branch you're referring to by which is checked out). It is very common for git users to switch between branches, and this is a fast operation in git.

To make a new branch equivalent to the current branch: 

git checkout -b <new_branch_name>

To switch from one branch to another, just check out the other branch: ((( git checkout <other_branch> }}}

Note git will not let you switch to a different branch if you have uncommitted changes in tracked files. To get around this, the simplest thing to do is to commit your modified files in a temporary commit, then undo that commit later. You can also "stash" your work, which actually makes a commit on a special branch. Since it's easy to forget what's in the stash, unless you're only stashing briefly, a real commit with an informative message is probably better.

To list all the branches in the repository: 

git branch -v

The -v (for verbose) tells git to show not just the branch names, but also the head commit's revision number and message.

To rename the current branch: 

git branch -m <new_branch_name>

To rename a branch that is not checked out: 

git branch -m <old_branch_name> <new_branch_name>

To delete a branch: 

git branch -d <branch_to_delete>

Under some circumstances, git will complain when you try to rename or delete a branch. If you are sure you want to do it, use -M instead of -m for rename, or -D instead of -d for delete.

If you will be working on a specific branch for a particular event (e.g. a deployment or hackathon), then you can add that branch to your local repository: 

git remote add <branch_name> https://github.com/flavour/<branch_name>.git
git fetch <branch_name>

Now you have both the master branch from the trunk repository, and the specific branch <branch_name>.

You can push branches other than master to your GitHub repository. 

git push -u origin <branch_name>

Note it is good to specify the branch name to push, else git will try to push all of them. The -u tells git to make your local branch "track" the remote branch. This is only needed on the first push to that branch.

If you need a specific revision of the current branch, your can check out that revision on a new branch: 

git checkout -b <revision> <branch_name>

(git requires a name for a branch if you want to preserve commits.)

Creating a second working directory and repository

If you wish to have multiple directories containing different branches, you can run these as separate web2py applications. (Note this is not a standard manner of working when using git, and is generally only needed if you are working on multiple projects at the same time, and need to preserve their databases and other state.)

  • Create a fresh clone: 
    cd web2py/applications
git clone git@github.com:flavour/eden.git <new_repository>
  • Setup a new repository on GitHub -- see: ​https://github.com/repositories/new
  • Add remotes. 
    git remote add upstream git@github.com:flavour/eden.git
git remote add origin git@github.com:<my_git_username>/<new_repository>.git
  • Push to GitHub: 
    cd <new_repository>
git push -u origin master

Using Patches

If you have made changes to one branch & wish to backport them to another branch, then this is done most easily using a Patch:

Story Branches

The ​Story Branch pattern allows pushing interim work to GitHub for review & also allowing contributing quick fixes to Trunk without needing to complete the interim work: 

git checkout -b <mystory>

git commit -a
...
git commit -a

# Quick review of code (no test code left in, etc)
git diff master...HEAD

​https://docs.google.com/drawings/d/1Vhvm1EmqWOVNZkZsiJ0MLLpdTl6H_ya263Tdb2HK1N0/edit

Developer Configuration

Tell git your name and email, which it uses to identify you as the author of commits. And tell it your account on GitHub. 

git config --global user.name "Your Name"
git config --global user.email your@email.com
git config --global github.user yourgithubusername
git config --global github.token yourtoken

These are examples of other settings you can change. The values shown are not necessarily ones you'll want to use. For instance, the choice of diff and merge tools is contentious -- use your favorites. 

git config --global core.editor "'C:/Program Files (x86)/Notepad++/notepad++.exe' -multiInst -notabbar -nosession -noPlugin"
git config --global merge.tool diffmerge
git config --global diff.tool diffmerge
git config --global difftool.diffmerge.cmd 'C:/Program Files (x86)/Git/etc/wrappers/git-diff-diffmerge-wrapper.sh' "$LOCAL" "$REMOTE"
git config --global difftool.prompt false
git config --global merge.tool diffmerge
git config --global mergetool.diffmerge.cmd 'C:/Program Files (x86)/Git/etc/wrappers/git-merge-diffmerge-wrapper.sh' "$PWD/$LOCAL" "$PWD/$BASE" "$PWD/$REMOTE" "$PWD/$MERGED"
git config --global mergetool.prompt false
git config --global mergetool.trustExitCode false
git config --global mergetool.keepBackup false

An alternative to diffmerge is Perforce's free P4V:

Windows

Install ​Console & ​Diffmerge & ​configure Powershell.

Developer Tools

.gitattributes runs version.py to update the VERSION file on commit

Possibly we could add a pre-commit hook to run tests, e.g. based on ​http://tech.yipit.com/2011/11/16/183772396/ or ​http://blog.penzilla.net/2011/09/git-pre-commit-hook-for-python-now-with.html

Notifications

You can subscribe to commits via RSS, e.g. to subscribe to Trunk, use:

If you wish to receive email notification of commits, then you can use an Email to RSS service like:

Resources

History

Why?

Sahana Eden has decided to move from Bzr/LaunchPad to Git/GitHub

  • The current repository is huge & bloated, taking too long to download.
  • Even simple changes take an age to Pull down to servers
  • Web2py no longer supports Bzr/LaunchPad, so we want to be able to maintain a common tool to work with both repositories.
  • New developers are likely to be more familiar with Git/GitHub

How?

The preferred approach is to have a clean repository, in order to get the maximum benefit from the migration...although it is technically possible to ​migrate the commit history. Commit History will instead be maintained on the LaunchPad site as an archive

Migrating existing Branches

Merge branch with trunk using normal Bzr tools

Assuming that you have already ​forked Eden Trunk, then you will need to create a new repository manually for additional branches, as you cannot ​fork your own project on GitHub:

  • ​https://github.com/repositories/new 
    cd web2py/applications
git clone git@github.com:flavour/eden.git <mybranch>2
  • Move .git & .gitignore from <mybranch>2 to <mybranch>
  • Delete the rest of <mybranch>2
  • Edit .git/config: 
    [remote "origin"]
    fetch = +refs/heads/*:refs/remotes/origin/*
    url = git@github.com:<mygitusername>/<mybranch>.git
  • Create the initial repo for this new branch 
    cd <mybranch>
git add .
git commit -am "Initial Git version of My branch"
git push -u origin master
git remote add upstream git://github.com/flavour/eden.git

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