Submitting patches

Setting up user information

Please set up consistent user information before starting with your real name and working\ email address on all your computers. For quick reference, here are the needed commands:

git config --global "Your Name Comes Here"
git config --global

Branching out

Create a new branch starting from master. Each branch should contain logically related commits (for example the implementation of a single feature), not a mixed bag of random changes.

If your change is depending on some other fix or feature that is not in master yet, you may start from next, but be aware that there is a small risk that the branch will be rebased.

Committing the patch

  • Make separate commits for separate changes. If you cannot describe what the commit does in one sentence, it is probably a mix of logically separate changes and should be separated into several commits.
  • Make sure that each commit can be compiled and that it works.
  • Use the imperative mode in the commit message when describing what you have done: use “change”, “add”, “fix”, not “changed”, “added”, “fixed”. Use the present tense to describe the current implementation: “feature X has an enormous potential for improvements” rather than “feature X had an enormous potential…” (While this writing style may seem awkward to begin with, you’ll find that it is actually easier to read and write.)
  • The first line of the commit message should describe concisely what the commit does. Leave out the full stop. (This line will be visible in gitk or in git log --oneline, so it should be understandable by itself.)
  • The second line in the commit message should be blank.
  • The body of the commit message should primarily answer the question why? rather than how?. That is, the most important is why the change was made, what bug it corrected or why anyone would want to use the new feature it implements. (Imagine yourself five years in the future trying try to figure why anyone would ever want this feature…) Technical details can also be useful, especially why one design was chosen rather than another design (again, imagine yourself investigating a bug and wondering why would anyone chose this way to implement this feature…).
  • Line break the commit message to lines no longer than approximately 70 characters (otherwise they are difficult to read in gitk).
  • Do not commit out-commented code or files that are no longer needed.
  • Check for unnecessary whitespace before committing with git diff --check.

Sending the patch

Use the “Pull request” button at GitHub.

Receiving your patch

When we receive your patch, we will do one of the following:

  • If there are simple things that will need to be fixed (for example, providing more information in the commit message instead of in the email), we may ask you to do that.
  • Otherwise, if your patch is not obviously wrong or inappropriate, we will merge it to the pu (“proposed updates”) branch.
  • Otherwise, if it is obviously wrong or inappropriate, we will tell you so. Reasons for immediate rejections include (but are not limited to):
  • Blatantly breaking backward compatibility.
  • Obviously unsafe coding practices or highly non-portable code.
  • Mixing of many difference changes and/or unnecessary re-indentation of code that is not changed. We will ask you to separate the changes into separate commits and/or branches and not change indentation of unchanged code.

You should not base any branches on pu branch, as it will be rewinded (rebuilt from scratch) frequently.


Patches will “cook” in the pu branch until they graduate or are dropped.

The following may happen to a patch (one or more times):

  • If build problems are found or there are many failing test cases not found before it was been included in pu, it may be removed from pu until the problems have been fixed.
  • Anyone can criticize, suggest improvements, or report that a patch breaks existing applications. If the serious problems remain, and no good way of fixing them can be found, the patch may be dropped.
  • Patches with known issues that have been inactive for a long time (several months) will be dropped.

This page is adapted from the similar page from the erlang/otp wiki, but any errors are entirely ours.

Did you find errors in the documentation? Do you have improvements to suggest? Suggest edits!