RFR: [lworld] Switch JLink to not use ImageReader API [v5]

[Roger Riggs]

On Wed, 5 Nov 2025 14:15:08 GMT, David Beaumont <duke at openjdk.org> wrote:

>> Creates a new, narrowed API explicitly for use by jlink, which view the resource entries in a jimage file without the re-mapping of names and invention of synthetic entries inherent in ImageReader.
>> 
>> Another good reason to express this new API as something other than ImageReader is that, to fix issues such as [JDK-8357249](https://bugs.openjdk.org/browse/JDK-8357249), we don't want to have the (System)ImageReader class used directly in jlink code. It's just the wrong abstraction and will make it harder to refactor jlink to use a non-singleton API with a controlled lifetime later. 
>> 
>> I've not added unit tests for the new API (yet), but the fact the PackagedModulesVsRuntimeImageLinkTest passes with preview content in the jimage file means that it's working as expected.
>
> David Beaumont has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Tidied up diff code in test.

src/java.base/share/classes/jdk/internal/jimage/BasicImageReader.java line 365:

> 363:                 if (name.startsWith("/modules/") || name.startsWith("/packages/")) {
> 364:                     throw new IllegalArgumentException("Invalid entry name: " + name);
> 365:                 }

This is already covered by the == null case below. The distinguished exception isn't necessary.

src/java.base/share/classes/jdk/internal/jimage/ResourceEntries.java line 35:

> 33:  * <p>This API is designed only for use by the jlink classes, which manipulate
> 34:  * jimage files directly. For inspection of runtime resources, it is vital that
> 35:  * {@code previewMode} is correctly observed, making this API unsuitable.

This would be more clearly stated as use API xxx to access the classes and resources of a runtime.

src/java.base/share/classes/jdk/internal/jimage/ResourceEntries.java line 56:

> 54:      * name (e.g. {@code "/<module-name>/..."}).
> 55:      */
> 56:     Stream<String> entryNamesIn(String module);

Are these names useful with any ImageReader api other than sizeOf or open?

src/java.base/share/classes/jdk/internal/jimage/ResourceEntries.java line 56:

> 54:      * name (e.g. {@code "/<module-name>/..."}).
> 55:      */
> 56:     Stream<String> entryNamesIn(String module);

Those extra words at the end of the method name are not consistent with naming conventions in openjdk.
Drop the "In".

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1721#discussion_r2494836681
PR Review Comment: https://git.openjdk.org/valhalla/pull/1721#discussion_r2494742427
PR Review Comment: https://git.openjdk.org/valhalla/pull/1721#discussion_r2494774562
PR Review Comment: https://git.openjdk.org/valhalla/pull/1721#discussion_r2494788265