RFR: 8345259: When linking from the run-time image ALL-MODULE-PATH is not accepted

[Mandy Chung]

On Mon, 2 Dec 2024 18:25:22 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

> Please review this bug fix for using `jlink` when linking from the run-time image. For regular JDK builds which include the `jmods` folder, that path is automatically added as the `--module-path` when not otherwise specified on the command line. For JDK builds with JEP 493 enabled, the `jmods` folder doesn't exist and the list of module roots needs to be computed from the system modules. However, since `jdk.jlink` isn't allowed to be added to the list of output modules when linking from the run-time image, the default module path doesn't include `jdk.jlink` and modules depending on `jdk.jlink`, currently only `jdk.jpackage`. This seems a sensible default since otherwise linking using ALL-MODULE-PATH fails, while it works with a JDK build including JMODs. See the bug for details about the issue.
> 
> When an explicit module path is being added, there is no difference. All modules on that path will be added as roots. Tests have been added for the same. Thoughts?
> 
> Testing:
> - [x] GHA, `test/jdk/tools/jlink` (all pass)
> - [x] Added jlink test.

Sounds good to me.   If `--add-modules ALL-MODULE-PATH` is given, jlink will find all observable modules from `--module-path` and use them as the root modules.  If the root set is empty, error; otherwise, it will link with the application modules on the module path and its transitive dependences.

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PR Comment: https://git.openjdk.org/jdk/pull/22494#issuecomment-2515384768