# Guidelines for PROJ code contributors¶

This is a guide for PROJ, casual or regular, code contributors.

## Code contributions.¶

Code contributions can be either bug fixes or new features. The process is the same for both, so they will be discussed together in this section.

### Making Changes¶

• Create a topic branch from where you want to base your work.
• You usually should base your topic branch off of the master branch.
• To quickly create a topic branch: git checkout -b my-topic-branch
• Make commits of logical units.
• Check for unnecessary whitespace with git diff --check before committing.
• Make sure your commit messages are in the proper format.
• Make sure you have added the necessary tests for your changes.
• Make sure that all tests pass

### Submitting Changes¶

• Push your changes to a topic branch in your fork of the repository.
• Submit a pull request to the PROJ repository in the OSGeo organization.
• If your pull request fixes/references an issue, include that issue number in the pull request. For example:
Wiz the bang

Fixes #123.

• PROJ developers will look at your patch and take an appropriate action.

### Coding conventions¶

#### Programming language¶

PROJ is developed strictly in ANSI C 89.

#### Coding style¶

We don’t enforce any particular coding style, but please try to keep it as simple as possible. If improving existing code, please try to conform with the style of the locally surrounding code.

#### Whitespace¶

Throughout the PROJ code base you will see differing whitespace use. The general rule is to keep whitespace in whatever form it is in the file you are currently editing. If the file has a mix of tabs and space please convert the tabs to space in a separate commit before making any other changes. This makes it a lot easier to see the changes in diffs when evaluating the changed code. New files should use spaces as whitespace.

#### File names¶

Files in which projections are implemented are prefixed with an upper-case PJ_ and most other files are prefixed with lower-case pj_. Some file deviate from this pattern, most of them dates back to the very early releases of PROJ. New contributions should follow the pj-prefix pattern. Unless there are obvious reasons not to.

## Tools¶

### cppcheck static analyzer¶

You can run locally scripts/cppcheck.sh that is a wrapper script around the cppcheck utility. It is known to work with cppcheck 1.61 of Ubuntu Trusty 14.0, since this is what is currently used on Travis-CI (travis/linux_gcc/before_install.sh). At the time of writing, this also works with cppcheck 1.72 of Ubuntu Xenial 16.04, and latest cppcheck master.

cppcheck can have false positives. In general, it is preferable to rework the code a bit to make it more ‘obvious’ and avoid those false positives. When not possible, you can add a comment in the code like

/* cppcheck-suppress duplicateBreak */


in the preceding line. Replace duplicateBreak with the actual name of the violated rule emitted by cppcheck.

### CLang Static Analyzer (CSA)¶

CSA is run by the travis/csa build configuration. You may also run it locally.

Preliminary step: install clang. For example:

wget http://releases.llvm.org/6.0.0/clang+llvm-6.0.0-x86_64-linux-gnu-ubuntu-14.04.tar.xz
tar xJf clang+llvm-6.0.0-x86_64-linux-gnu-ubuntu-14.04.tar.xz


Run configure under the scan-build utility of clang:

./clang+llvm-6.0.0-x86_64-linux-gnu-ubuntu-14.04/bin/scan-build ./configure


Build under scan-build:

./clang+llvm-6.0.0-x86_64-linux-gnu-ubuntu-14.04/bin/scan-build make [-j8]


If CSA finds errors, they will be emitted during the build. And in which case, at the end of the build process, scan-build will emit a warning message indicating errors have been found and how to display the error report. This is with someling like

./clang+llvm-6.0.0-x86_64-linux-gnu-ubuntu-14.04/bin/scan-view /tmp/scan-build-2018-03-15-121416-17476-1


This will open a web browser with the interactive report.

CSA may also have false positives. In general, this happens when the code is non-trivial / makes assumptions that hard to check at first sight. You will need to add extra checks or rework it a bit to make it more “obvious” for CSA. This will also help humans reading your code !

### Typo detection and fixes¶

Run scripts/fix_typos.sh

### Include What You Use (IWYU)¶

Managing C includes is a pain. IWYU makes updating headers a bit easier. IWYU scans the code for functions that are called and makes sure that the headers for all those functions are present and in sorted order. However, you cannot blindly apply IWYU to PROJ. It does not understand ifdefs, other platforms, or the order requirements of PROJ internal headers. So the way to use it is to run it on a copy of the source and merge in only the changes that make sense. Additions of standard headers should always be safe to merge. The rest require careful evaluation. See the IWYU documentation for motivation and details.

IWYU docs