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Submitting patches

RaimoNiskanen edited this page · 38 revisions


The recommended way of sending patches is described on this page. Basically, you push your changes to a git repository and send us an email with a reference to your public git repository and branch.

If you follow the instructions, you should receive a response within one workday.

By following the instructions, you will help to minimize the time Erlang/OTP team spends doing unproductive work, and that will ultimately be of benefit for all users of Erlang/OTP.

What will happen with patches sent as attachments?

If you send us a patch in other ways than described on this page, it will mean more work for us and we cannot guarantee anything. It is up to the maintainer for that part of OTP to decide whether (s)he will pick up the patch.

That said, if your patch fixes a bug that we consider severe (for example, bugs that are likely to hit many users and cause the system not to start, corrupt data, or cause a crash), we will take care of it anyway. (We never apply patches without verification, so “take care of” may mean that we will correct the bug in a way that we’ll find better.)

What about pull requests?

We prefer emails, so that the discussion about patches will get archived so that other people can learn from them.

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 example the same email addressed that is subscribed
erlang-patches mailing list). 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 dev (the development branch for the next release). You can do this via the following instructions (assuming you already have a github account and you are signed in):

  • Browse to the Erlang/OTP git project page and hit the little ‘fork’ button to create your own fork of the repository (you only have to do this once).
  • After the ‘hardcore forking action’ has completed, checkout a copy of your new fork via ‘your’ clone url:
    git clone
  • cd into the new ‘otp’ directory created.
  • Create a remote pointing to the OTP master repository.
    git remote add upstream git://
  • Create a new remote branch to hold your changes (use a descriptive name for the particular change you’re making):
    git push origin origin:refs/heads/new_feature_name
  • Start tracking the new branch (this will switch you to the new branch too):
    git checkout --track -b new_feature_name origin/new_feature_name
  • Pull in all the changes from the dev branch on the otp remote into your new branch:
    git pull upstream dev
  • Make your changes, commit them according to the guidelines and then send the OTP team a fetch request.
  • If it take you a while to finish your changes or you need some update from a newer dev than you branched from, rebase your branch on dev. After checking out your branch:
    git fetch upstream
    git rebase upstream/dev
    … And fix any merge conflicts. Do not merge from dev since we want a straight chain of commits based on a fairly recent dev.
  • If you create a patch based on someone else’s you can do exactly that: branch from someone else’s branch (that branches from a fairly recent dev).

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

See forking tips on GitHub, for managing the OTP team branches as the upstreams.

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.
  • To make it possible to use the powerful git bisect command, make sure that each commit can be compiled and that it works.
  • Do not commit commented-out code or files that are no longer needed.
  • Check for unnecessary whitespace before committing with git diff --check.

Making a patch OTP-worthy

The following steps are not necessary if you only want feedback on a proposed change, but are ultimately necessary if you want it to be included in OTP.

  • If you are fixing a bug, write a test case before fixing the bug (so that you’ll know that the test case catches the bug). For applications without a test suite in the git repository, it would be appreciated if you provide a small code sample in the commit message or email a module that will provoke the failure.
  • If you are implementing a new feature, also write a new test case and/or test_SUITES. (Note: The primary reason for writing test cases is not to prove that the new feature works correctly, but to make sure that it will be noticed if future changes — perhaps to code that seems unrelated — break the feature.)
  • If you are implementing a new feature, also update the documentation to describe the feature.
  • Make sure that existing test cases don’t fail.
  • Make sure that the patch builds and works on all major platforms (many patches we receive works on Linux but not on Windows).
  • Make sure that the patch does not break backward compatibility. In general, we only break backward compatibility in major releases and only for a very good reason and usually after first deprecating the feature one or two releases beforehand.
  • In general, language changes/extensions or major updates to Kernel and Stdlib also require an EEP (Erlang Enhancement Proposal) to be written and approved before they can be included in OTP.
  • Make sure that your changes follow the coding and indentation style of the code surrounding your changes. (At some point in the future, there will be a style guide, either included in the documentation or on some web site, but it is not ready yet.)
  • In most code (Erlang and C), indentation is 4 steps using tabs and spaces. Tabs are always 8 steps. (If you use Emacs, use Erlang-mode, and add (setq c-basic-offset 4) to .emacs to get C code correctly indented.)

Sending the patch

Send an email to with a reference to your github repository and name of the branch to pull from. To make it really easy for us to fetch the patch, please include the entire git command. For example:

git fetch git:// my-cool-updates

my-cool-updates is the name of the branch.

(We also accept inline patches compatible with format generated by git format-patch, but please make sure that your email client has not garbled the message.)

Receiving your patch

When we receive your patch, we will do one of the following (typically within a workday):

  • 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 will 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, even if it lacks test cases and/or documentation (i.e. it need not be OTP-worthy).
  • 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 rebuilt from scratch on top the current development branch frequently.

Currently in the ‘pu’ branch


We run automatic tests and builds of the pu branch.

If a branch include in pu causes a build problem, that branch will be dropped. We will reinstate the branch if/when we receive a correction.

We might also drop a branch if it causes test case to fail (depending on both the number of failed test cases as well as the kind of failures).


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 a patch is not OTP-worthy, it can be replaced with a new or extended version, either by the original author or by someone else.
  • If build problems are found on some platform (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 will be dropped.


Usually a patch will graduate to the dev branch when it passes the criteria for OTP-worthiness. Usually the maintainer for the application in question will decide when a patch will graduate, but for larger patches and for patches on the borderline of breaking backward compatibility, several people in the OTP group may be involved in the decision.

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