On Fri, 10 Oct 2025 11:30:19 GMT, David Beaumont <[email protected]> wrote:

>> Adds support for writing preview related flags into jimage files.
>> 
>> Preview mode is complex. It's not nearly as simple as "does something in 
>> /modules/xxx/... have an entry in /modules/xxx/META-INF/preview/...".
>> 
>> Specific issues include:
>> 
>> Supporting preview-only resources without forcing a double lookup on 
>> everything.
>> Changing the set of entries in /packages/xxx directories to account for 
>> preview only packages in some modules.
>> Minimising the work done during image reader initialization to only need to 
>> process the small number of preview resources (rather than scanning the 
>> whole file to look for them).
>> The new flags added by this code address these issues, but calculating them 
>> correctly with only minor adjustments to the existing code was not feasible, 
>> it just became a lot larger and very complex.
>> 
>> To address this, a new type (ModuleReference) is introduced to track and 
>> then merge information about packages seen in each module. This allows a 
>> much simpler inner loop for processing resource paths when building the node 
>> tree, combined with a subsequent merging stage to produce the final package 
>> information for each module.
>> 
>> Not that since ModuleReference is needed during jimage reading, that class 
>> is already present in the previous PR on which this is based, but it starts 
>> to be used to calculate the module flags in this PR.
>> 
>> This PR can also adds the ImageReader unit tests for preview mode, which 
>> rely on being able to generate jimage files with preview mode flags in.
>> 
>> Compare and review this against 
>> https://github.com/openjdk/valhalla/pull/1619.
>
> David Beaumont has updated the pull request incrementally with one additional 
> commit since the last revision:
> 
>   feedback and remove unused code

src/jdk.jlink/share/classes/jdk/tools/jlink/internal/BasicImageWriter.java line 
39:

> 37:     public static final String MODULES_IMAGE_NAME = "modules";
> 38: 
> 39:     private final ByteOrder byteOrder;

Made obvious fields final and removed unused, non-public, code.

-------------

PR Review Comment: 
https://git.openjdk.org/valhalla/pull/1621#discussion_r2419590040

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