Development practices

Development practices

Making changes to GDAL
Minor changes to GDAL, such as bug fixes, may be made by opening a GitHub pull request.
Major changes should be discussed on the gdal-dev listserv and may require the drafting
of a RFC (request for comment) document.
GDAL's policy on substantial code additions is documented at RFC 85: Policy regarding substantial code additions.

Git usage
This section collects a few best practices for git usage for GDAL development.

Initiating your work repository
Fork OSGeo/gdal from the GitHub UI, and then run:
git clone https://github.com/OSGeo/gdal
cd gdal
git remote add my_user_name git@github.com:my_user_name/gdal.git

Working with a feature branch
git checkout master
# potentially update your local master against upstream, as described above
git checkout -b my_new_feature_branch

# do work. For example:
git add my_new_file
git add my_modifid_message
git rm old_file
git commit -a

# you may need to resynchronize against master if you need some bugfix
# or new capability that has been added since you created your branch
git fetch origin
git rebase origin/master

# At end of your work, make sure history is reasonable by folding non
# significant commits into a consistent set
git rebase -i master
# use 'fixup' for example to merge several commits together,
# and 'reword' to modify commit messages

# or alternatively, in case there is a big number of commits and marking
# all them as 'fixup' is tedious
git fetch origin
git rebase origin/master
git reset --soft origin/master
git commit -a -m "Put here the synthetic commit message"

# push your branch
git push my_user_name my_new_feature_branch

From the GitHub UI, issue a pull request.
If the pull request discussion or automated checks require changes, commit
locally and push. To get a reasonable history, you may need to combine commits
using git rebase -i master, in which case you will have to force-push your
branch with git push -f my_user_name my_new_feature_branch.

Updating your local master against upstream master
git checkout master
git fetch origin

# Be careful: this will lose all local changes you might have done now
git reset --hard origin/master

Commit messages
Commit messages should indicate a component name (eg a driver name), a short
description, and when relevant, a reference to a issue (with 'fixes #' if it
actually fixes it)
COMPONENT_NAME: fix bla bla (fixes #1234)

Details here...

Commit hooks
GDAL provides pre-commit hooks to run code linters before a commit is made. The
hooks are cloned with the repository and can be installed using
pre-commit:
python3 -m pip install pre-commit
pre-commit install

Once installed, the hooks can be run manually via pre-commit run --all-files.

Blame ignore file
Due to whole-tree code reformatting done during GDAL 3.7 development,
git blame information might be misleading. To avoid that, you need
to modify your git configuration as following to ignore the revision of
the whole-tree reformatting:
git config blame.ignoreRevsFile .git-blame-ignore-revs

Backporting bugfixes from master to a stable branch
git checkout master
With git log, identify the sha1sum of the commit you want to backport
git checkout 2.2 # if you want to backport to 2.2
git pull origin 2.2
# git checkout -b branch_name  # if you intend to submit the backport as a pull request
git cherry-pick the_sha1_sum
git push ...

If changes are needed, do them and git commit -a --amend

Things you should NOT do
(For anyone with push rights to OSGeo/gdal) Never modify a commit or
the history of anything that has been
committed to https://github.com/OSGeo/gdal
Committing symbolic links is allowed only under the .github directory in order to
avoid potential problems on Windows.