On Fri, 6 Mar 2026 18:57:31 GMT, Jan Lahoda <[email protected]> wrote:
>> There's an enum >> `src/java.base/share/classes/jdk/internal/javac/PreviewFeature.java#PreviewFeature.Feature` >> that defines the current preview features, in particular those that have an >> API. The API is then marked with the appropriate enum constant. >> >> There's a problem with this enum: javac's APIs may also need to use >> constants from the enum, and as javac is built twice, once with the >> bootstrap JDK to get the so called "interim javac" (which is then used to >> compile nearly all the rest of the JDK), and second time to get the final >> version of javac, this enum needs to be dragged into the interim compilation >> as well. >> >> As a consequence, the bootstrap JDK classfiles are resolved against this >> up-to-date feature enum. And if any of the bootstrap JDK classfiles would >> refer to an enum constant that is not part of this up-to-date feature enum, >> javac would report a warning, failing the build. >> >> As a consequence, the guidance is that when a preview feature ceases to be >> preview (either by maturing to a final and permanent feature, or by >> removal), we keep the appropriate enum constant as long as the bootstrap JDK >> may use it. >> >> This works, but causes constant confusion, and unnecessary work, as >> finalizing a preview feature requires another action in the next release to >> cleanup the enum constant. >> >> This PR is exploring an alternative solution: it takes the up-to-date >> `Feature` enum, and auto-generates a hybrid enum containing constants both >> from the up-to-date and bootstrap `Feature` enum. As a consequence, the >> up-to-date enum does not need to contain any legacy constants, as those are >> automatically injected for the interim build. This hybrid enum should never >> be used outside of the interim javac build. >> >> As a consequence, when a feature ceases to be a preview feature, we can >> clean up the feature enum immediately, leading to less confusion and less >> downstream work. > > Jan Lahoda has updated the pull request incrementally with one additional > commit since the last revision: > > Removing an unnecessary dependency as suggested. Looks reasonable ------------- Marked as reviewed by liach (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/30072#pullrequestreview-3905771022
