3. Development Process

As common in open source projects, contributions of code and documentation to the project are highly appreciated. The QGIS community is very supportive. This section describes the procedure for developing and merging your contributions in the QGIS project.

3.1. A git based project 

The complexity of the QGIS source code has increased considerably during the last years. Therefore it is hard to anticipate the side effects that the addition of a feature will have. In the past, the QGIS project had very long release cycles because it was a lot of work to reestablish the stability of the software system after new features were added. To overcome these problems, QGIS switched to a development model using the git version control system: new features are coded in the contributor branches first and merged to the QGIS master (the main branch) when they are finished and stable.

QGIS source code is hosted at https://github.com/qgis/QGIS.

3.1.1. Roles 

There exist various roles on GitHub. When having an account on GitHub you are already allowed to contribute by forking the repository and have the role ‘contributor’. Core developers are ‘collaborators’ and can merge branches into the upstream and official repository.

3.1.2. Environment 

To get started using and contributing to the QGIS repository, you need to:

have a GitHub account
make your own copy of the QGIS repository (see fork)
have a git client installed on your system
set up your git environment
and have fun!

3.1.3. Installing git 

The git project provides recent versions of the software for most platforms. Follow the instructions at https://git-scm.com/downloads to get and install the copy corresponding to your OS and architecture. There, it’s also possible to install a git GUI client to browse and manage your repositories (most of the time, it will install git if not yet available).

3.2. Development in branches 

3.2.1. Contributions to development 

Once signed up on GitHub and having forked the repository, you can engage as a contributor.

Note

Contributions to QGIS code can be done from your forked repository on the GitHub website. The new code will automatically be built by the test environment. But this workflow can quickly reveal its limits when you want to provide complex changes. Instructions below will assume a local clone.

You can contribute by initiating a pull request. To do that follow these generic steps:

Clone your repository onto your local computer and set up the build environment
Create a new branch and do the edits for development
Commit your changes and push your branch back to the remote fork on GitHub. A pull request is then offered as web link (URL) right after.
Open a pull request (PR) asking to pull the commit(s) from your branch into the master branch into the upstream repository.
A review process is being started informing other contributors and collaborators about your pull request. You should be reactive to their comments and suggestions.

Note

A more detailed Github’s Fork & Pull Workflow is available at https://reflectoring.io/github-fork-and-pull/

Note

Most of the QGIS projects (website, documentation, pyQGIS API, plugins…) are available in the project GitHub page and can get contributions, following the same process.

3.2.2. Accessing the Repository 

To be able to interact from your local disk with both your remote fork and the QGIS upstream repositories, you need to:

Make a clone of your copy on your local disk

cd path/to/store/the/repository
git clone https://github.com/<yourName>/QGIS.git

Connect the QGIS main repository (we will name it upstream) to yours
```
git remote add upstream https://github.com/qgis/QGIS.git
```

Check connected remote repositories

git remote -v
# origin   https://github.com/<YourName>/QGIS.git (fetch)
# origin   https://github.com/<YourName>/QGIS.git (push)
# upstream https://github.com/qgis/QGIS.git (fetch)
# upstream https://github.com/qgis/QGIS.git (push)

Your online repository is now accessible from your local drive and you can interact with it using the name origin. Whenever you’d like to fetch changes from the qgis/QGIS repository, use upstream.

Note

In QGIS we keep our most stable code in the current release branch. master branch contains code for the so called ‘unstable’ release series. Periodically we will branch a release off master, and then continue stabilisation and selective incorporation of new features into master.

See the INSTALL file in the source tree for specific instructions on building development versions.

3.2.3. Procedure 

Initial announcement on mailing list or issues repo:
Before starting, make an announcement on the developer mailing list to see if another developer is already working on the same feature. You can also mention your interest as a comment in the issue report if one exists in the repo. If the new feature requires any changes to the QGIS architecture, a QGIS Enhancement Proposal (QEP) is needed.
Create a branch in your local repository:
Create a new git branch for the development of the new feature, based on latest state of the master branch.
git fetch upstream master git checkout -b newfeature upstream/master
Now you can start developing:
Code your changes in your local disk with your usual IDE. Remember to write tests suite for your modifications, when appropriate.

Proper formatting and spell check

Make sure your code is properly formatted and spelled by running the prepare commit script before issuing git commit.

./scripts/prepare_commit.sh

This can be automated by adding it to a pre-commit hook, for example:

# check if a pre-commit already exists and backup it
test -e .git/hooks/pre-commit && mv .git/hooks/pre-commit pre-commit.000
# copy prepare_commit.sh as new pre-commit hook
cp ./scripts/prepare_commit.sh .git/hooks/pre-commit

The spell checker script can also be run alone with:

./scripts/astyle_all.sh

Commit your changes to the git repo:
When making a commit, put a descriptive comment and rather do several small commits if the changes across a number of files are unrelated. Conversely we prefer you to group related changes into a single commit.
git add path/to/your/files git commit -m "Add a comment describing your nice feature"
Without the -m option, a new editor window will open for you to write your commit message.

Here are some recommendations about commit description format.
Now, you may want to share your work with QGIS community members. Push your new feature up to your online fork repository by doing:
```
git push origin newfeature
```
Note

If the branch already exists, your changes will be pushed into it, otherwise, it is created.
Submit your changes with a pull-request
With opening the pull-request, the automated test suite is triggered and checks whether your changes follow the coding guidelines of QGIS and do not break any existing feature. You’d need to fix any reported issues before your branch is merged upstream.

Tip

We use GitHub actions to manage the tests to be run on the repository. For convenience, you can enable the actions on your repository so that the tests are run when you push the changes. You’d then open the pull request after they all passed, making the review process more efficient.
Rebase to upstream master regularly:
It is recommended to rebase to incorporate the changes in master to the branch on a regular basis. This makes it easier to merge the branch back to master later. After a rebase you need to git push -f to your forked repo.
git pull --rebase upstream master git push -f origin newfeature

Note

See the following sites for information on becoming a GIT master.

3.2.4. Testing before merging back to master 

When you are finished with the new feature and happy with the stability, make an announcement on the developer list. Before merging back, the changes will be tested by developers and users.

3.3. Submitting Pull Requests 

There are a few guidelines that will help you to get your patches and pull requests into QGIS easily, and help us deal with the patches that are sent to use easily.

In general it is easier for developers if you submit GitHub pull requests. We do not describe Pull Requests here, but rather refer you to the GitHub pull request documentation.

If you make a pull request we ask that you please merge master to your PR branch regularly so that your PR is always mergeable to the upstream master branch.

Pull requests will cause various checks of the Continuous Integration (CI) system to run: building for different environments and running tests, running code linters, spell checkers, etc. Make sure to look at the results of those ckecks and try to address issues they raise. Of course, you can ask a question in the pull request if you need help from other developers to understand and/or resolve an issue.

If you are a developer and wish to evaluate the pull request queue, there is a very nice tool that lets you do this from the command line

In general when you submit a PR you should take the responsibility to follow it through to completion - respond to queries posted by other developers, seek out a ‘champion’ for your feature and give them a gentle reminder occasionally if you see that your PR is not being acted on. Please bear in mind that the QGIS project is driven by volunteer effort and people may not be able to attend to your PR instantaneously. We do scan the incoming pull requests but sometimes we miss things. Don’t be offended or alarmed. Try to identify a developer to help you and contact them asking them if they can look at your patch. If you feel the PR is not receiving the attention it deserves your options to accelerate it should be (in order of priority):

Help review others pull requests to free the person assigned to yours.
Send a message to the mailing list ‘marketing’ your PR and how wonderful it will be to have it included in the code base.
Send a message to the person your PR has been assigned to in the PR queue.
Send a message to the project steering committee asking them to help see your PR incorporated into the code base.

3.3.1. Best practice for creating a pull request 

Always start a feature branch from current master.
If you are coding a feature branch, don’t “merge” anything into that branch, rather rebase as described in the next point to keep your history clean.
Before you create a pull request do git fetch upstream and git rebase upstream/master (given upstream is the remote for qgis user and not your own remote, check your .git/config or do git remote -v | grep github.com/qgis).
You may do a git rebase like in the last line repeatedly without doing any damage (as long as the only purpose of your branch is to get merged into master).
Attention: After a rebase you need to git push -f to your forked repo. CORE DEVS: DO NOT DO THIS ON THE QGIS PUBLIC REPOSITORY!

3.3.2. Special labels to notify documentors 

There is a special label (Needs Documentation) that can be assigned by reviewers to your pull request to automatically generate issue reports in QGIS-Documentation repository as soon as your pull request is merged. Remember to mention whether your feature deserves such a label.

Moreover, you can add special tags to your commit messages to provide more information to documenters. The commit message is then added to the generated issue report:

[needs-docs] to instruct doc writers to please add some extra documentation after a fix or addition to an already existing functionality.
[feature] in case of new functionality. Filling a good description in your PR will be a good start.

Please devs use these labels (case insensitive) so doc writers have issues to work on and have an overview of things to do. BUT please also take time to add some text: either in the commit OR in the docs itself.

3.3.3. Due Diligence 

QGIS is licensed under the GPL. You should make every effort to ensure you only submit patches which are unencumbered by conflicting intellectual property rights. Also do not submit code that you are not happy to have made available under the GPL.

3.4. Pull Requests merge criteria 

Pull requests must be approved by at least one Core Developer (a developer with push rights to the qgis/QGIS GitHub repository). Before merging, the Core Developer must ensure that the PR passes all reasonable CI checks. Some exceptions exist to this rule, e.g. when a check is broken for unrelated reasons (such as broken third party services, or a lint/code analysis/spell check test failing from other parts of a modified file).

Pull requests created by a Core Developper must also be approved by at least another Core Developer.

A PR must remain open for at least 24 hours following submission, even if it has already been approved. This is to allow wider feedback to be gathered prior to merge, and to permit pre-merge feedback from developers in other time zones. Exceptions to this policy are:

Approved pull requests for backports to stable branches
“Emergency” pull requests, eg those which fix broken master builds, CI infrastructure or which represent a time-sensitive security risk
Trivial fixes. The definition of “trivial” is left open to common sense and developer discretion, but is expected to include non-risky changes like typo fixes, translation string fixes, tab order changes, or similar.

3.5. Obtaining GIT Write Access 

Write access to QGIS source tree is by invitation. Typically when a person submits several (there is no fixed number here) substantial patches that demonstrate basic competence and understanding of C++ and QGIS coding conventions, one of the PSC members or other existing developers can nominate that person to the PSC for granting of write access. The nominator should give a basic promotional paragraph of why they think that person should gain write access. In some cases we will grant write access to non C++ developers e.g. for translators and documentors. In these cases, the person should still have demonstrated ability to submit patches and should ideally have submitted several substantial patches that demonstrate their understanding of modifying the code base without breaking things, etc.

Note

Since moving to GIT, we are less likely to grant write access to new developers since it is trivial to share code within github by forking QGIS and then issuing pull requests.

Always check that everything compiles before making any commits / pull requests. Try to be aware of possible breakages your commits may cause for people building on other platforms and with older / newer versions of libraries.