> 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. ------------- Changes: - all: https://git.openjdk.org/jdk/pull/30072/files - new: https://git.openjdk.org/jdk/pull/30072/files/cf6e6e40..58e0bae4 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=30072&range=01 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=30072&range=00-01 Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod Patch: https://git.openjdk.org/jdk/pull/30072.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/30072/head:pull/30072 PR: https://git.openjdk.org/jdk/pull/30072
