Backwards Compatibility
OpenZeppelin Contracts uses semantic versioning to communicate backwards compatibility of its API and storage layout. Patch and minor updates will generally be backwards compatible, with rare exceptions as detailed below. Major updates should be assumed incompatible with previous releases. On this page, we provide details about these guarantees.
Bear in mind that while releasing versions, we treat minors as majors and patches as minors, in accordance with semantic versioning. This means that v2.1.0 could be adding features to v2.0.0, while v3.0.0 would be considered a breaking release.
API
In backwards compatible releases, all changes should be either additions or modifications to internal implementation details. Most code should continue to compile and behave as expected. The exceptions to this rule are listed below.
Security
Infrequently, a patch or minor update will remove or change an API in a breaking way but only if the previous API is considered insecure. These breaking changes will be noted in the changelog and release notes, and published along with a security advisory.
Errors
The specific error format and data that is included with reverts should not be assumed stable unless otherwise specified.
Major releases
Major releases should be assumed incompatible. Nevertheless, the external interfaces of contracts will remain compatible if they are standardized, or if the maintainers judge that changing them would cause significant strain on the ecosystem.
An important aspect that major releases may break is "upgrade compatibility", in particular storage layout compatibility. It will never be safe for a live contract to upgrade from one major release to another.
In the case of breaking "upgrade compatibility", an entry to the changelog will be added listing those breaking changes.
Storage layout
Patch updates will always preserve storage layout compatibility, and after v2.0.0-alpha.0 minors will too. This means that a live contract can be upgraded from one minor to another without corrupting the storage layout. In some cases it may be necessary to initialize new state variables when upgrading, although we expect this to be infrequent.