Development with Git

Work in Progress

This page is a work in progress. If you have notes/hints/tips on DSpace development with Git/GitHub, please feel free to suggest their addition, or even add them to this page directly.

DSpace on GitHub

The DSpace GitHub code repository can be found at: https://github.com/DSpace/DSpace

Git Resources

A list of some possibly useful external Git resources:
(Feel free to add to the list)

Intro to Git for those who know SVN: http://git.or.cz/course/svn.html
Pro-Git Book (Online) -> Great intro to Git in general
Git Community Book (Online) -> Another great Git introduction
Git Reference -> This site is a great reference for various Git commands that are available
Fedora Developers' list of useful Git Resources
Fedora Developers' Git Guidelines and Best Practices (not all are Fedora specific)
Fedora Developers' Git Quick Start Guide
Chris Wilper's (Fedora Committer) tips/rules on using Git: https://wiki.duraspace.org/display/~cwilper/How+I+Use+Git

Still want to use SVN locally, even though DSpace is on GitHub?

GitHub does provide some basic SVN client support (e.g. SVN checkout): https://github.com/blog/966-improved-subversion-client-support
- UPDATE: GitHub now supports more advanced SVN client support: https://github.com/blog/1178-collaborating-on-github-with-subversion
Or, you could obviously download the zipped-up DSpace release packages and import them into your local SVN

Overview of the Git Lifecycle

(Borrowed from Fedora's Git Guidelines and Best Practices)

Git allows a developer to copy a remote subversion repository to a local instance on their workstation, do all their work and commits in that local repository, then push the state of that repository back to a central facility (github).

Bearing in mind that you will always being doing your work and commits locally, a typical session looks like this:

Get a copy of the central storage facility (the repository). This is how you download a copy of the DSpace Source Code (i.e. [dspace-source]), but this source code directory also is a valid local git repository. In the below example, we've called this directory "dspace-src", but you can call it whatever you want.
```
git clone git@github.com:DSpace/DSpace.git dspace-src
cd dspace-src
```
Create a localbranch called "DS-123". This is what is traditionally called a "topic" or "feature" branch in Git. You are creating a branch to work on a specific topic or feature (in this case a ticket named "DS-123").
```
git branch DS-123
```
Create a local copy of the branch from master (if it doesn't exist) and make it your active working branch. You are now developing on the DS-123branch.
```
git checkout DS-123
```
Now, start creating, editing files, testing. When you're ready to commit your changes:
```
git add [file]
```
This tells git that the file(s) should be added to the next commit. You'll need to do this on files you modify, also.
Commit your changes locally. This only modifies your localcopy of the repository, and the commits only happen in your local "DS-123" branch.
```
git commit [file]
```
Now, the magic:
```
git push origin DS-123
```
This command pushes the current state of your local repository, including all commits, up to github ("origin" repository). Your work becomes part of the history of the public "DS-123" branch on github.

git push is the command that changes the state of the remote code branch. Nothing you do locally will have any affect outside your workstation until you push your changes.

git pull is the command that brings your current local branch up-to-date with the state of the remote branch on github. Use this command when you want to make sure your local branch is all caught up with changes push'ed to the remote branch.

Some useful Git terms

master: this is the main code branch, equivalent to trunk in Subversion. Branches are generally created off of master. However, it is usually recommended that you not do your work directly in the master branch. Instead, you should look to create new branches frequently (e.g. a new branch for each feature/ticket you are working on), and once that work is completed, merge it back into the master branch. Both branching and merging are much easier in Git, and should become a part of your daily development practices. For more information, see Pro-Git's chapter on "Basic Branching & Merging"

origin: the default remote repository (at GitHub) that all your branches are pull'ed from and push'ed to. This is defined when you execute the initial git clone command. For more information see Pro Git's chapter on "Working with remotes"

unpublished vs. published branches: an unpublished branch is a branch that only exists on your local workstation, in your local repository. Nobody but you know that branch exists. A published branch is one that has been push'ed up to GitHub, and is available for other developers to checkout and work on.

fast-forward: the process of bringing a branch up-to-date with another branch, by fast-forwarding the commits in one branch onto the other. For more information, see Pro-Git's chapter on "Basic Branching & Merging"

rebase: the process by which you cut off the changes made in your local branch, and graft them onto the end of another branch. It also lets you reorganize or combine local commits in order to "clean up" your commit trail before you share it publicly via GitHub. For more information, see Pro-Git's chapter on Rebasing and GitHub's 'rebase' page.

Some useful Git Development Guidelines

The DSpace Developers/Committers are still working on our Git Guidelines & Best Practices.

But in the meantime, here's some development guidelines from a few "third parties" (feel free to add additional links)

Very widely used & popular model: "A successful Git branching model" ('git-flow' branching model)
- There are also "git-flow" tools available at: https://github.com/nvie/gitflow These tools give you quick ways to create the various types of branches described in the above model (release / feature / hotfix branches)
Chris Wilper's "How I Use Git" (His perspective based slightly off a response to the above "git-flow" model)
Fedora Developers' Git Guidelines and Best Practices (not all are Fedora specific) - this is how they approach team development in Git
Hydra Developers' Guidelines for Committers (similar to Fedora's) and Guidelines for Contributors (using Pull Requests)
Github-flow, which is used within Github. It is similar to the Fedora model, but incorporates code review: http://scottchacon.com/2011/08/31/github-flow.html (Ryan Scherle mentions Dryad is also looking at this model)

Getting Started with DSpace + Git

Clone the repository. (The git repo is ~65MB). In the below example, we named the local directory "dspace-src", but you can name it whatever you want.

git clone git://github.com/DSpace/DSpace.git dspace-src
cd dspace-src

At this point, you now have a copy of the DSpace Source Code (i.e. [dspace-source]), and you are checked out to the branch master (master is akin to SVN trunk), which will work, but it is the bleeding edge of development and not recommended for production instances.

If you would like to develop on DSpace for your local needs (University, Library, or Institution), you are encouraged to fork this GitHub repository (see also #Developing from a Forked Repository section below), and commit your changes to your personal/organizational repository. We recommend that you build your repository off of a released "tag" of DSpace such as dspace-1.8.2. The benefit of being based off of a tag/release-branch is that releases have a series of testing phases to ensure high quality, and there is some maintenance of bug and security fixes.

git checkout dspace-1.8.2

From there, you can follow the standard DSpace build instructions in order to build/install DSpace from the source code. For example:

mvn package 
cd dspace/target/dspace-[version]-build.dir
ant update 
/etc/init.d/tomcat6 restart

Sample Git Development Workflows

Developing from a Forked Repository

This approach is recommended for all DSpace developers (especially non-Committers), as it allows developers to store their own local customizations in their own forked GitHub repository.

Although the below instructions only detail how to perform these tasks via the command-line, some developers may find that an Integrated Development Environment (IDE) will provide the same Git commands/options. For more information on using DSpace with an IDE, see the list of IDEs at: Developer Guidelines and Tools

Fork the DSpace GitHub Repo to store your local changes: As GitHub describes in their "Fork a Repo" guide, forking lets you create your own personal copy of the codebase. It not only provides you a place to put your local customizations. It also provides an easier way to contribute your work back to the DSpace community (via a GitHub Pull Request as described in the "#Contributing Changes/Patches to DSpace via GitHub" section below).
- You can fork the repository directly from the GitHub User Interface. Just create an account at GitHub. Then browse to the DSpace GitHub repository (https://github.com/DSpace/DSpace) and click the "Fork" button at the top of the page. This creates a full copy of that repository under your GitHub account (e.g. https://github.com/\[your-username\]/DSpace)
Clone your GitHub Repo to your local machine.So, now that you have a fork of the DSpace GitHub repository, you'll want to "clone" your repository to your local machine (so that you can commit to it, etc.). You can clone it to whatever directory you wish. In the below example we call the directory "dspace-src":
```
git clone git@github.com:[your-username]/DSpace.git dspace-src
cd dspace-src
```
You now have the full DSpace source code, and it's also in a locally cloned git repository!
For easier Fetches/Merges, setup an "upstream" repository location. If you have forked the DSpace GitHub repository, then you may want to setup an "upstream" remote that points at the central DSpace GitHub repository. It basically just provides you with an easier to remember "name" for the central DSpace GitHub repository. This is described in more detail in the GitHub "Fork a Repo"guide. Perform the following:
```
git remote add upstream git://github.com/DSpace/DSpace.git
```
(Technically you can name it something other than "upstream". But, "upstream" is just the GitHub recommended naming convention).
Create a branch for each new feature/bug you are working on. Because Git makes branching & merging easy (see Pro-Git's chapter on "Basic Branching & Merging"), you should create new branches frequently (even several times a day) and avoid working directly in the master branch(unless you are making a very minor change). In this case, we'll create a local branch named "DS-123" (note that this branch only exists on your local machine so far). We'll also perform a "checkout" in order to switch over to using this new branch.
```
git branch DS-123
git checkout DS-123
```
Do your development work on your new branch, committing changes as you go. Note that at this point, you are only committing changes to your local machine. Nothing new will show up in GitHub yet, until you pushit there. This is a very basic example of a single file commit, but you get the idea.
```
git commit NameOfFileToCommit.java
```
Optionally, you can push these changes and this branch up to GitHub.If you want to share your work more publicly, you can push the changes and your new branch up to your GitHub repository:
```
git push origin DS-123
```
In this command "origin" is actually the name of the repository that you initially cloned. This pushes your new branch up to GitHub, so that it is publicly available to other developers.
Once you are finished, merge your changes back to master branch. The "master" branch is where all your completed code should eventually be merged ("master" is loosely equivalent to "trunk" in Subversion). So, once you are done with the branch development, you should merge that code back into "master". Luckily, Git makes this simple and will figure out the best way to merge the code for you. In rare situations you may encounter conflicts which Git will tell you to resolve. For more details, see Pro-Git's chapter on "Basic Branching & Merging". In order to perform the merge, you'll first need to switch over to the "master" branch (the branch you are merging into):
```
git checkout master
git merge DS-123
```
There! You've now merged the changes you made on the "DS-123" branch into the "master" branch!
Optionally, push this merge up to GitHub.Again, at any time, you can push your local changes up to GitHub for public sharing. So, if you want to push your newly merged "master" branch, you'd do the following:
```
git push origin master
```
(I.e. You are pushing your local "master" branch up to the "origin" repository at GitHub. Remember, "origin" refers to the repository you initially cloned, which in this example would be your personal GitHub repo that you cloned in Step #1 above.)
Once your branch is no longer needed, you can delete it.Really, there's no need to keep around all these small branches! Once the changes you made have been merged into "master" and you no longer have any other use for the branch you created, just delete it! Here's an example of deleting the "DS-123" branch from both your local machine and from GitHub (if you shared it there)
```
# Remove the branch locally first
git branch -d DS-123
# If you have pushed it to GitHub, you can also remove it there by doing a new push (notice the ":")
git push origin :DS-123
```
Fetch changes from central DSpace GitHub.New changes/updates/bug fixes happen all the time. So, you want to be able to keep your "fork" up-to-date with the central DSpace GitHub. In this case, you now can take advantage of the "upstream" remote setting that you setup back in Step #2 above. If you recall, in that step, you configured "upstream" to actually point to the central DSpace GitHub repo. So, if there are changes made to the central DSpace GitHub, you can fetch them into your "master" branch as follows:
```
# Fetch the changes from the repo you named "upstream"
git fetch upstream
```
What this command has done is actually create a new "upstream/master" branch (on your local machine) with the latest changes to be merged from that "upstream" repository.
Merge changes into your Local repository.Remember, "fetching" changes just brings a copy of those changes down to your local machine. You'll then need to merge those changes into your "master" branch, and optionally push the changes back to your personal public GitHub repository.
```
# First, make sure we are on "master" branch
git checkout master
# Now, merge the changes in the "upstream/master" branch into my "master" branch
git merge upstream/master
```
In this case, Git will attempt to merge any new changes made in the "upstream" repository into your local "master" branch.
Push those merged changes back up to GitHub.Once you are up-to-date, you may now want to push your latest merge back up to your public GitHub repository.
```
git push origin master
```

Additional Handy Git Commands

git status - At any time, you may use this command to determine the status of your local git repository and how many commits ahead or behind it may be from the "origin" repository at GitHub. It also tells you if you have local changes that you haven't yet committed. For more info type: git help status
git log - At any time, you may use this command to see a log of recent commits you've made to the current branch. For more info type: git help log
git diff - At any time, you may use this command to see differences of your current in progress work. For more info type: git help diff
git pull - Can be used instead of using git fetch followed by git merge. A "pull" does both a fetch and an automated "merge" in a single step.
git stash (See also: Stashing) - Allows you to temporarily "stash" uncommitted changes. This command is extremely useful if you want to do a "pull" or "merge" but were working on something else. You can temporarily "stash" what you are working on to perform the merge/pull, and then use git stash apply to reapply your stashed work.
git rebase (See also: Rebasing) - This tool is extremely powerful, and can be used to reorganize or combine commits that have been made on a local branch. It can also be used in place of a "merge" (in any of the situations described above). However, as it changes your commit history, you should NEVER USE REBASE ON ANY BRANCH THAT HAS BEEN PUBLICLY SHARED ON GITHUB. For more information, see Pro-Git's chapter on Rebasing and GitHub's 'rebase' page.
git cherry-pick - useful to grab a single commit into current branch from any of the local branches or remote branches added locally. A handy use-case is when we have a master branch and a bugfix branch (e.g. dspace-3_x) and you want a bugfix to go to both branches, you can commit to either branch, then switch to the other and execute "git cherry-pick [commit-hash]". Don't forget to push both branches, as usual.

GitHub tips

If you want to show someone the diff between two commits, you can do it directly using GitHub functionality. Example:

https://github.com/DSpace/DSpace/compare/fde129026febcd58af030e14c7a7f82bd201033b...dspace-3.0

As you can see, the commit can be specified either as a hash or as a tag (they're interchangable). Bonus tip: the two commits don't even have to be in the same repository, so you can compare e.g. your fork to the official repo.

Contributing Changes/Patches to DSpace via GitHub

While we're still working out the ideal workflow for contributions, existing Committers will have direct push access to the DSpace GitHub repo, while contributors are encouraged to submit a Pull Request for review.

A few notes on creating a proper "Pull Request"

Please, make sure to create a "Pull Request" from a branch and NOT from your "master". (You'll understand exactly why after reading #2)
Be warned that any additional changes/commits you make to that branch (before the "Pull Request" is accepted/merged) will immediately be included in that existing "Pull Request". This means that, if you want to continue your local development, you mustcreate that "Pull Request" from a semi-static branch (so that any additional commits you make on "master" in the meantime don't get included as part of the existing "Pull Request").
- The reason why this occurs is that a "Pull Request" just points at a specific "branch" (the branch it was initialized from). It does NOT point at a specific set of commits. So, when the "Pull Request" is accepted/merged, you are pulling in the latest version of that "branch". For more information, closely read the GitHub help page on Pull Requests, specifically noting the following statement:
  Pull requests can be sent from any branch or commit but it’s recommended that a topic branch be used so that follow-up commits can be pushed to update the pull request if necessary.
Once your "Pull Request" is created, you can use the GitHub Pull Request tools to communicate with the Committer who is assigned to the Pull Request. If further changes are requested, you can make those changes on the branch where you initiated the Pull Request (and those changes will automatically become part of the Pull Request, as described above)

Common DSpace Git/GitHub Issues

Maven Error: "*/src/main/webapp" does not exist

If you have checked out DSpace 1.8.2 or previous via GitHub, the first time you build DSpace, Maven may error out with a message similar to:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-war-plugin:2.1.1:war (default-war) on project dspace-sword-client-xmlui-webapp: Execution default-war of goal org.apache.maven.plugins:maven-war-plugin:2.1.1:war failed:  basedir /dspace-src/dspace-sword-client/dspace-sword-client-xmlui-webapp/src/main/webapp does not exist -> [Help 1]

This error is essentially an artifact of DSpace only supporting SVN in previous releases. Unfortunately, although these "/src/main/webapp/" empty directories existed in SVN, they are ignored by Git/GitHub. This is due to Git's inability to track empty directories.

So, if you run into any error while trying to recompile with mvn package that a specific "src/main/webapp" directory does not exist, then you will have to create that directory. The DSpace GitHub repository has since fixed this issue (on the latest "master" code and all future releases). But if it affects you, then these are the steps to fix this.

First, create the missing "src/main/webapp" directories. For example, these are the ones missing in Git for DSpace 1.8.x:

mkdir -p dspace-sword-client/dspace-sword-client-xmlui-webapp/src/main/webapp/
mkdir -p dspace/modules/jspui/src/main/webapp  
mkdir -p dspace/modules/lni/src/main/webapp  
mkdir -p dspace/modules/oai/src/main/webapp  
mkdir -p dspace/modules/solr/src/main/webapp  
mkdir -p dspace/modules/sword/src/main/webapp  
mkdir -p dspace/modules/swordv2/src/main/webapp  
mkdir -p dspace/modules/xmlui/src/main/webapp

In each directory, put a place-holder ".gitignore" file, so that Git tracks the directory. For example:

touch dspace-sword-client/dspace-sword-client-xmlui-webapp/src/main/webapp/.gitignore
touch dspace/modules/jspui/src/main/webapp/.gitignore
touch dspace/modules/lni/src/main/webapp/.gitignore  
touch dspace/modules/oai/src/main/webapp/.gitignore  
touch dspace/modules/solr/src/main/webapp/.gitignore  
touch dspace/modules/sword/src/main/webapp/.gitignore  
touch dspace/modules/swordv2/src/main/webapp/.gitignore  
touch dspace/modules/xmlui/src/main/webapp/.gitignore

Then, rebuild DSpace!

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