RFR: 8317620: Build JDK tools with ModuleMainClass attribute

[Erik Joelsson]

On Wed, 1 Nov 2023 19:58:07 GMT, Mandy Chung <mchung at openjdk.org> wrote:

> Tool modules can be created via `jmod --main-class` option such that `ModuleMainClass` attribute will be added in `module-info.class` and the module's main class can be launched via `java -m <module-name>` without specifying the name of the main class.
> 
> In addition, for modules with `ModuleMainClass` attribute, jlink will pre-resolve the module graph such that when such module is launched at runtime (without `--add-modules` or `--limit-modules` option), the runtime can skip the module resolution and speed up the startup time.
> 
> This PR extends the build system to allow a module to specify the main class under `make/modules/$MODULE/Jmod.gmk` file.    Also JDK tools with a single entry point (or a primary entry point) are candidates to add `ModuleMainClass` attribute in `module-info.class` to benefit from the jlink optimization.   For example, `java -m jdk.jpackage` will be launched using the pre-resolved module graph.
> 
> Verified manually by running `java -m $MODULE` on the modules with main class.

Looks ok from a build point of view.

make/Main.gmk line 410:

> 408: 	+($(CD) $(TOPDIR)/make && $(MAKE) $(MAKE_ARGS) \
> 409: 	$(patsubst %,-I%/modules/$1,$(PHASE_MAKEDIRS)) \
> 410: 	    -f CreateJmods.gmk MODULE=$1)

Suggestion:

	+($(CD) $(TOPDIR)/make && $(MAKE) $(MAKE_ARGS) \
	    $(patsubst %,-I%/modules/$1,$(PHASE_MAKEDIRS)) \
	    -f CreateJmods.gmk MODULE=$1)

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

Marked as reviewed by erikj (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16463#pullrequestreview-1710257242
PR Review Comment: https://git.openjdk.org/jdk/pull/16463#discussion_r1380113539