GRASS GIS is written in more than one programming language. While most of the source code is written in C, about 30% is written in Python. A compiler is needed to convert the C/C++ source code into executable files ("binaries"). In contrast, Python is an interpreted language that can only be executed with Python software.
Now, in order to create an installable binary package from a source code package, the so-called "compilation step" is required. While the source code consists of thousands of C and Python files (plus HTML documentation), the included "makefiles" tell the build system to generate binaries from the source code in the correct order, render the manual pages, etc.
The way to install the compiler tools and Python depends on the operating system. To make this easier, we have collected copy-paste instructions for most operating systems in our wiki:
Contributions other than code
There is more than one way of contributing, see full list at https://grass.osgeo.org/get-involved/. In the rest of this document, we will focus on contributions centered around the GRASS GIS source code.
Reporting issues and suggesting features
To report an issue or to suggest features or a change, open an issue on GitHub.
Changing code and documentation
This guide covers contributing to the main version of GRASS GIS source code which is in the branch called main. It assumes that you have some very basic knowledge of Git and GitHub, but if you don't just go through some tutorial online or ask on the GRASS GIS developer mailing list.
First time setup
- Create an account on GitHub.
- Install Git on your computer.
- Set up Git with your name and email.
- Fork the repository (by clicking the
Forkbutton in the upper right corner of the GitHub interface).
- Clone your fork (use SSH or HTTPS URL):
git clone email@example.com:your_GH_account/grass.git
- Enter the directory
- Add main GRASS GIS repository as "upstream" (use HTTPS URL):
git remote add upstream https://github.com/OSGeo/grass
- Your remotes now should be "origin" which is your fork and "upstream" which is this main GRASS GIS repository. You can confirm that using:
git remote -v
- You should see something like:
origin firstname.lastname@example.org:your_GH_account/grass.git (fetch) origin email@example.com:your_GH_account/grass.git (push) upstream https://github.com/OSGeo/grass.git (fetch) upstream https://github.com/OSGeo/grass.git (push)
It is important that "origin" points to your fork.
Update before creating a feature branch
- Make sure your are using the main branch to create the new branch:
git checkout main
- Download updates from all branches from the upstream remote:
git fetch upstream
- Update your local main branch to match the main branch in the upstream repository:
git rebase upstream/main
Update if you have local branches
rebase fails with "error: cannot rebase: You have unstaged changes...",
then move your uncommitted local changes to "stash" using:
- Now you can rebase:
git rebase upstream/main
- Apply your local changes on top:
git stash apply
- Remove the stash record (optional):
git stash pop
Creating a new feature branch
Now you have updated your local main branch, you can create a feature branch based on it.
- Create a new feature branch and switch to it:
git checkout -b new-feature
You can use your favorite tools to change source code or other files in the local copy of the code. When make changes, please follow Submitting Guidelines at http://trac.osgeo.org/grass/wiki/Submitting.
- Add files to the commit (changed ones or new ones):
git add file1 git add file2
- Commit the change (first word is the module name):
git commit -m "module: added a new feature"
Pushing changes to GitHub
- Push your local feature branch to your fork:
git push origin new-feature
When you push, GitHub will respond back in the command line to tell
you what URL to use to create a pull request. You can follow that URL
or you can go any time later to your fork on GitHub, display the
new-feature, and GitHub will show you button to create
a pull request.
After creating a pull request
GRASS GIS maintainers will now review your pull request. If needed, the maintainers will work with you to improve your changes.
Once the changes in the pull request are ready to be accepted, the maintainers will usually squash all your commits into one commit and merge it to the main branch.
Once the pull request is merged, it is a good time to update your local main branch in order to get the change you just contributed.
GRASS GIS maintainers use additional workflows besides the one described above. These are detailed at https://trac.osgeo.org/grass/wiki/HowToGit