The Squeak Development Process

The Squeak Development Process supports the improvement of Squeak—the core of the system and its supporting libraries—by its community. The process builds on few basic ideas: the use of Monticello as the primary source code management system, free access for the developers to the main repositories, and an incremental update process for both developers and users.

Monticello Repositories

The main development repository is The Trunk:

New code will be committed here; the repository is world-readable and writable for the group of core developers.

The main contribution repository is The Inbox:

This repository is intended as dropbox. It is world-readable and world-writable. Everyone is encouraged to contribute code here. Code that the community, after discussion, accepts as fitting will be moved to the trunk.

If contributions do not work, are deemed unfitting, or become obsolete for another reason, they are moved to The Treated Inbox for future reference:

Developer access

The board manages developer access to the repositories at Very active contributors can ask the board for direct write access to the trunk. Anybody can suggest other contributors for trunk access.

How Commits to the Inbox are Merged

If a change in the inbox is accepted the following should be done by a core developer to merge it:

  1. Merge the commit in an up-to-date trunk image
  2. Make sure the commit works with the up-to-date image
  3. Commit the merged version
  4. The merge commit has now two ancestors: the previous head of the trunk repository and the commit from the inbox. To provide a consistent history, we have to move the inbox commit to the trunk repository. Therefore go to and look for the commit under versions. After clicking on the version you see details of the version and two buttons which allow you to move the version either to trunk or the treated inbox. Use the move to trunk button to move the change to the trunk.

In case there are no new commits in the trunk repository, core developers can also simply use the “Move to Trunk” button on

How to Remove a Package from Trunk

  1. First, do NOT delete the package from! Leave it in for older images.
  2. Note the version of the package to be removed.
  3. Edit the Squeak-Version package, altering the postscript to remove the package (MCPackage named: 'Universes') unload. You get to the postscript by pressing the Scripts button in the Monticello Browser when the package is selected.
  4. Save the Squeak-Version package to trunk with a version that is increased by the removed package version (step 2 above) + 1 for this bump. This keeps the trunk version number correctly increasing like it should.
  5. Update the trunk update config with the latest version of packages - and REMOVE the package from the config that should no longer be in trunk. Save this update.
  6. Test it with a new image to verify everything worked correctly.

How to Deprecate a Class or Method

When a single meta object is removed from the image we want to make sure that projects relying on it can still be loaded in newer Squeak versions. Therefore, these methods and classes are saved in special packages. The packages are named using the following pattern: “NNDeprecated-OriginalPackageName” (NN being the two digit version number). So, if we want to deprecate meta objects from the “Kernel” package which were part of the base system up to Squeak 5.1, we would put them into the package: “51Deprecated-Kernel”.

In detail, the process for classes or methods works as following:

Deprecating a Class

  1. Move the class to the corresponding deprecation category.
  2. Remove all references to it from the Trunk image.

Deprecating a Message/Method

  1. Move the method to the method category “NNDeprecated-OriginalPackageName” to make it an extension method persisted in the corresponding deprecation package.
  2. Remove all calls to the deprecated method from the Trunk image.
  3. Maybe rewrite the deprecated method to use the new implementation, if there is one.
  4. Add self deprecated: 'Use this or that instead.'. at the beginning of the deprecated method to guide foreign application code through the migration.


All code submitted to the repositories must be licensed under The MIT License. If code represents any kind of artistic work (e.g., serialized icons or sounds) not covered by this license, please choose one that shares a similar spirit. Creative Commons falls in this category. Add a note to the respective code artifact such as in a method or class comment.

Rules of Engagement

Here are some useful guidelines:

  • Merge often. In particular when you pick up work and immediately before you intend to commit.

  • Exercise caution. This is a running system and breaking it carelessly is generally frowned upon.

  • Restrain yourself. Getting developer access does not mean you are free to put in every extension you always wanted to have without discussion.

  • If in doubt, ask. This is the corollary to the restrain yourself rule. You are not under pressure to ship a product, so you have the time to send a note saying something like “I am planning to fix this old issue and it may have some side effect here or there. Please advise.”

  • You break it, you fix it. If you change something, you are generally expected to take care of problems caused by this change. Though there are exceptions. If in doubt, please ask.

  • Do good and talk about it. When you are done with whatever you have been working on, let people know about it. It can be as short as a note to Squeak-dev saying “I have fixed the long standing bug with xyz. Please update and enjoy.”

  • Unit Testing. Unit tests are an essential part of maintaining the reliability of our releases. New unit tests are always welcome. Keep in mind that a unit test should take as little time to run as possible. Maintaining the reliability of Squeak is always easier when all tests pass: If you break something, the appearance of a new failure or error is immediately obvious and the cause is more easily found. To that end fixes for failures or errors are extremely valuable. Also, please avoid submitting changes that cause failures or errors themselves.