Introduction

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:

Compile and install instructions

Contributing

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 Fork button in the upper right corner of the GitHub interface).
Clone your fork (use SSH or HTTPS URL):

git clone git@github.com:your_GH_account/grass.git

Enter the directory

cd grass/

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	git@github.com:your_GH_account/grass.git (fetch)
origin	git@github.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

If rebase fails with "error: cannot rebase: You have unstaged changes...", then move your uncommitted local changes to "stash" using:

git stash

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

Making changes

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.

Committing

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

Pull request

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 branch 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.

Further notes

GRASS GIS maintainers use additional workflows besides the one described above. These are detailed at https://trac.osgeo.org/grass/wiki/HowToGit

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