Creating A Patch

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If you want to submit improvements to the FPC or Lazarus code, you need to submit a patch which developers can easily merge.


  1. .po translation files should be sent as whole files
  2. new files should be sent as whole files, with instructions where they should be placed


You need the trunk/development version of Lazarus (or FPC). You can get Lazarus using either SVN or Git.


Note: If you submit patches, do not base them on stable versions of Lazarus/FPC. Typically the development version is very different from stable versions as many improvements and fixes have been applied by the developers

Platform differences

The instructions later assume you have opened a command prompt and moved (cd) to the directory of the repository. Here are the details :


Assuming you checked out Lazarus into C:\lazarus, open command prompt (cmd.exe) and type "cd \lazarus".

*nix systems

Assuming you checked out Lazarus into ~/lazarus, open terminal and type "cd ~/lazarus".

Creating a patch using SVN

svn diff > mypatch.diff

This includes all changed files in the whole SVN repository.

You can also define the individual files, to make sure no garbage is included, eg. :

svn diff ide/main.pp ideintf/objectinspector.pp > mypatch.diff

Note: If using TortoiseSVN on Windows, you can select the folder where Lazarus was checked out in Windows Explorer then right click to select TortoiseSVN->Create Patch...

See also TortoiseSvn#Troubleshooting if you have problems.

Creating a patch using Git

First, develop your code in a separate branch! While your development branch is active, you can create patches of all your local commits by :

git format-patch master

It creates a set of patches named like "0001-CommitMsg.patch", "0002-CommitMsg.patch" and so on.

If you want all the changes in one patch, either combine the commits using "git rebase -i ..." or use the following command :

git format-patch master --stdout > mypatch.patch

Note: "master" branch follows the SVN trunk by default when using git-svn link. However the mirror repository in GitHub uses "upstream" branch instead. Then you must replace "master" with "upstream" in the above commands.

Submitting the patch

Now you have a patch. I'd suggest to look the file over to see if it looks ok (no unexpected changes).

The recommended way to submit a patch is through the bug tracker, see How do I create a bug report for details. If there is a report for the issue your patch fixes, use that, otherwise create a new issue. Upload the file to attach it to the issue.

Using a forked Git repository directly

It is possible to use Git in a distributed manner also for Lazarus development. At least developers JuhaManninen and Alexander Klenin ("Ask") are ready to accept code in a Git repository.

In practice the repository must be forked from the Lazarus mirror in GitHub. The code must be in a separate branch and rebased against "upstream" branch. This is not tested yet, we can add more details here when somebody actually forks the repo and creates code.

The limitation of this model is that the code must belong to the area of expertise of the developers working with Git. If the code is outside that area, you can still use Git but you must create patches and send them to bug tracker.

Applying a patch

This explains how to apply somebody else's patch to your local repository. You can test the patch by using the --dry-run toggle switch like this:

patch --dry-run < somepatch.diff

The output of the patch program will be identical to the actual patching, only it does not alter the sourcecode files. Very handy for testing, without the possibility to screw up your source.

A patch made with "svn diff"

To do the final patching, use the following commandline:

patch < somepatch.diff

If that doesn't work because the path layout of your environment is different from the environment where the patch was created, you can tell patch to strip out all path information:

patch -p0 < somepatch.diff

Any GUI tool for diffs on Windows can handle these patches, too.

A patch made with "git format-patch"


Git itself applies the patch like this :

git apply 0001-gitpatch.patch


The "patch" command now supports git format patches with -p1. This is tested with patch v.2.6.1 on Linux, old versions may not support it.

patch -p1 < 0001-gitpatch.patch

"patch" is available for Windows, too, but there are also GUI tools for the job.


TortoiseMerge supports the Git format patch without problems. It is installed together with Tortoise SVN but is not integrated in explorer. It must be opened from the Start menu.

ToDo: add more GUI tools that support Git format patches


Finally, patches may have a Unix/Linux line ending (LF) while your local file has Windows (CR+LF) line endings or vice versa. You'll have to convert the patch file before applying on Windows at least, as the supplied patch.exe is picky about line endings.

On Windows, the patch.exe supplied with FPC/Lazarus is very picky; you may have better luck with the patch.exe supplied by Git:

"C:\Program Files (x86)\Git\bin\patch.exe" -p0 < mypatch.diff

... or the svn patch command available since SVN 1.7.

See also