Eclipse Plug-in Versioning Proposal

Summary
The Eclipse team currently changes their plug-in version numbers to match each major release of Eclipse (e.g., 2.1, 3.0). This is a convenient way of understanding the origin of plug-ins but do not capture the actual semantics of the changes which occurred. For example, the change from 2.1 to 3.0 indicates a major and incompatible change. Of course, this is generally not what was intended as most 3.0 plug-ins are in fact compatible with their 2.1 versions. Here we outline the current use of version numbers and propose a new process for using plug-in version numbering to better indicate levels of compatibility.
Last Modified: 1200 February 17, 2004

Problem Definition

Current Eclipse practice calls for the teams to increment plug-in version numbers to match the upcoming release of Eclipse. For example, about 6 months ago we changed our plug-in version numbers from 2.1 to 3.0.0. In June 2004 we will ship Eclipse 3.0.0 and all plug-ins (save a few third party ones) will be version 3.0.0. This is convenient because it allows people to look at the plug-in version number and immediatly understand what version of Eclipse that plug-in is from.

This approach has several drawbacks however

• Incrementing the major (first) version segment renders the plug-in "incompatible" with all previous versions of that plug-in. Dependent plug-ins which specify a version number (e.g., <import plugin="org.eclipse.foo" version="2.1.0"/>) will not resolve against version 3.0.0 of the prerequisite plug-in. Unresolved plug-ins cannot participate in a running Eclipse environment. Even though we have worked hard to make the content of the 3.0 plug-ins binary backward compatible, 2.1 based third party plug-ins (which specify prereq version numbers) require changes to work in 3.0.
• This approach does not set a good example. People building on top of Eclipse look to us to understand how they should structure their world. Following this model, plug-ins like EMF and GEF should increment their version numbers to match the Eclipse version numbers regardless of whether they changed at all. This has the nasty side effect of rendering all of their users incompatible as well. It also does not scale well as a little change at the bottom then ripples all the way up.
• Eclipse is getting away with this because a) we are at the bottom of the stack, b) we ship a single wad that is built, packaged and distributed in unison and c) we do not use version numbered prerequisites ourselves. It is really this last point which hurts the most. By not using versioned prereqs, we are not eating our own dog food. Clearly we do not mean that the resources plug-in from 3.0 will run on ANY version of the Eclipse runtime. People who build and distribute plug-ins are not generally able to play it quite so fast and loose.
• Features are not the cure. To address some of this, we use features and their abilily to group plug-ins. The assumption is that if the feature constraints are met, then the underlying plug-ins will all be happy and thus versioned plug-in dependencies are not needed. This works but assumes that the feature writer (may not be related to the plug-in authors) can understand the plug-in constraints well enough to define the feature. In practice this means that the plug-ins in the feature all have similar constraints such that they can be distilled to a smaller set of inter feature constraints. Features are a packaging mechanism for plug-ins. Pushing constraint satisfaction up to the packaging layer puts a significant load both on the people creating the packages (e.g., features) as well as the packaging (e.g., feature) mechanism.

Proposal

To address these concerns, we propose that the Eclipse SDK team start using the version number semantics defined by Eclipse for all their plug-ins. The numbering process works as follows:- new plug-ins start as 0.0.0 and go through various version numbers (<1.0.0) until they are ready for their first release. At that time, developers may choose to set the version number to 1.0.0. This is mostly cosmetic and is not required. Prior to first release the numbering process depends mostly on how widely availability and use of the early versions. For example, a beta at 0.9 sets a good tone and might encourage release at 1.0.0.

• Immediately after a release, plug-ins continue with the same number as they had in the release (e.g., 1.0.0).
• As the plug-in is developed for the next release, the version number is changed to accurately reflect those changes. For example, if some minor fixes are done, the service (third) segment should be incremented (e.g., 1.0.1). If significant but compatible rework is done and/or new function added, the minor (second) segment should be incremented. (e.g., 1.1.0). Note that in this example, the significant work overshadows the service fixes so the service (third) segment is set to 0. If major rework is done such that the new version is incompatible with previous versions then the major (first) segment should be incremented (e.g., 2.0.0) Note that the minor and service numbers are 0 here as well.
• A plug-in's version number need only be incremented to distinguish one release from another. For example, if we release 1.0.0 of a plug-in and then do some bug fixes for a milestone (say M3), we increment the version to 1.0.1. If that plug-in were eventually released, people could look at the version number and see that a) it is different from 1.0.0 and b) that some bug fixes were done. If instead, further bug fixes are done for M5, there is no need to further increment in the version number (i.e., to 1.0.2). Leaving the version at 1.0.1 still conveys the important information to users of the next release. Of course, teams could increment the version further if needed/desired. Either way, the qualifier (fourth) version segment can be used (e.g., 1.0.1.M3 vs 1.0.1.M5) to differentiate between builds of the same version.
• Plug-in version number changes are solely at the discretion of the plug-in development team. They are in the best position to understand their changes and the scope of impact.
• Features are used to group together plug-ins and label them with a particular "product" release version (e.g., 3.0). The org.eclipse.platform 3.0.0 feature contains a complete and precise specification of the plug-ins in the 3.0 platform.

Action

The only action required is to decide we want to do this and refine/document the details of the structure and process. There are no technological hurdles. Just as teams are responsible updating their copyright dates, they would be responsible for incrementing their plug-in versions. These changes are done very infrequently so will not be a particular burden.

If we decide to follow this new policy we can retrofit the 3.0 plug-ins with "correct" version numbers or start the new approach immediately following the release of Eclipes 3.0. Starting now avoids situations where Eclipse 2.1 based plug-ins do not work on the released 3.0 because of resolution problems (rather than because of actual incompatibilities). However, it may adversely affect people in the community who have already come to know, like and use the 3.0.0 version numbers.