On Thu, 5 Mar 2026 10:39:02 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. make/CompileInterimLangtools.gmk line 130: > 128: $$(INTERIM_LANGTOOLS_BASE_MODULES), $$(call > FindTransitiveDepsForModule, $1))) > 129: > 130: $$(BUILD_$1.interim): $$(foreach d, $$($1_DEPS_INTERIM), > $$(BUILD_$$d)) $(COPY_PREVIEW_FEATURES) Note how we declared a dependency from building of the interim module to `$(COPY_PREVIEW_FEATURES)` here. You replaced `$(COPY_PREVIEW_FEATURES)` with `$(BUILDTOOLS_OUTPUTDIR)/gensrc/java.base.interim/jdk/internal/javac/PreviewFeature.java` so you need to update this dependency declaration too. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/30072#discussion_r2890310638
