RFR: 8335989: Implement Module Import Declarations (Second Preview) [v5]

[Alan Bateman]

On Wed, 30 Oct 2024 15:25:24 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> This is a current patch for module imports declarations, second preview. At least the JEP number and preview revision will need to be updated in `jdk.internal.javac.PreviewFeature.Feature`, but otherwise I believe this is ready to receive feedback.
>> 
>> The main changes are:
>> - `requires transitive java.base;` is permitted, under the preview flag. Both javac and the runtime module system are updated to accept this directive when preview is enabled.
>> - the `java.se` module is using `requires transitive java.base;`, and is deemed to be participating in preview, so its classfile version is not tainted. Runtime is updated to access `requires transitive java.base;` in any `java.*`, considering all of them to be participating in preview. Can be tighten up to only `java.se` is desired.
>> - the types imported through module imports can be shadowed using on-demand imports. So, for example, having:
>> 
>> import module java.base;
>> import module java.desktop;
>> ...
>> List l;//ambigous
>> 
>> but:
>> 
>> import module java.base;
>> import module java.desktop;
>> import java.util.*;
>> ...
>> List l;//not ambigous, reference to java.util.List
>
> Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Moving operators to the beginning of line, as suggested.

Marked as reviewed by alanb (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/21431#pullrequestreview-2407660920