wiki:DeprecatingFeatures

Version 5 (modified by abarth@webkit.org, 9 years ago) (diff)

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Overview

We hope that the vast majority of features we add to WebKit will become widely implemented by other web rendering engines and enjoyed by authors and users for years to come. However, if we avoided landing code for a feature until we were sure that feature would be successful, we wouldn't be perpetually following rather than leading, and the web platform would not advance as quickly. This wiki page explains how to handle those cases in which we wish to remove a feature from WebKit.

Balancing costs and benefits

The guiding principle in our approach is to balance net costs of removing the feature against the net costs of retaining the feature. In many cases, evaluating these costs is a value judgement, and whenever possible, we should strive to replace opinion with data. The following are a number of factors we ought to consider when removing a feature:

  • Compatibility. The more a given feature is used, particularly on the web at large but also in "walled gardens" of content, the larger the compatibility cost of removing the feature. For example, we have not removed our implementation of SQLDatabase even though other browser vendors have refused to implement the feature and the W3C has removed the specification from the standards track. We've kept SQLDatabase because removing this API would break compatibility with a large number of consumers of WebKit that use this API.
  • Interoperability. If a feature fails to garner wide-spread implementation, then web sites that use that feature might work in one user agent but not in another. This lack of interoperability fractures the web platform, making it more difficult for users to switch from one user agent to another. Removing WebKit-proprietary features, or at least hiding them from the web platform, often improves interoperability.
  • Complexity. Each feature we include in WebKit increases WebKit's complexity, slowing down development of the engine. We try to reduce the complexity cost of features, for example by using Modules, but each feature still adds a non-zero cost (e.g., for project-wide improvements, like EfficientStrings). Remove a feature often reduces the complexity of WebKit.

XYZZY

How to determine if we can deprecate a feature

  • The burden on the overall project needs to be evaluated as it should be the primary driver for dropping any feature. Small features that require very little maintenance may not qualify under this rule and their deprecation would need to be argued extensively.
  • If the feature is used (e.g. MutationEvent), we need to show that we have a replacement that is better than the feature to be deprecated (better needs to be defined in the context of the deprecation and will need to be argued).
  • Deprecating a feature means we will remove it in the future. Deprecation is not meant as a usage metric collection or to assess web-developers' reactions.

Deprecation steps

  • Any deprecation should be sent to webkit-dev for discussion.
  • Any deprecation requires some data as to why the feature can be deprecated. The goal of the data is to show that the feature is not widely used and is not popular. The following would qualify:
    • usage statistics in the wild (either by instrumenting the browser or any other means).
    • some discussions on the standard mailing lists underlining that the standards' bodies don't think there is enough traction to get the feature standardized.
    • some proof that there is others way to achieve the same result that are better.
    • some proof that web-developers don't care much about this feature.
    • ...
  • If several vendors are supporting the feature, we expect people to have interacted with them to assess their support towards the removal.

Deprecating a prefixed feature

Deprecating a prefixed feature should be treated as deprecating an existing features and should follow the previous steps.