[lworld] RFR: 8376088: [lworld] value class creation in CompileJavaModules.gmk leaves unnecessary files [v2]

[David Beaumont]

On Thu, 22 Jan 2026 20:51:53 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>> make/CompileJavaModules.gmk line 182:
>> 
>>> 180:     $(MODULE_OUTPUTDIR)/_the.java.base.valueclasses: $($(MODULE)-$(VALUECLASSES_STR))
>>> 181: 		$(MKDIR) -p $(@D)/META-INF/preview
>>> 182: 		$(MV) $(TEMP_OUTPUTDIR)/$(MODULE)/*/ $(@D)/META-INF/preview
>> 
>> This could also be a `$(CP) -r` (with slight adjustment), but I'd want to still avoid copying the marker files.
>> The root module directory shouldn't contain any files we care about, so using '*/' suffix just copies directories and ignores marker files.
>> 
>> I *think* that because TARGETS doesn't have the compilation marker added to it, once the compilation marker files are created, they only serve to support other targets that depend upon them, which is only the valueclasses target.
>> 
>> If however, the Java compilation macro does have side effects visible to the rest of the build, this might not be a safe assumption. Please let me know if you think I've made an error here, and what your preferences are.
>
> By moving the class files instead of copying them, you are disabling any incremental build logic provided by javac and the plugins we use when compiling the value classes. There are most likely other potential issues that I'm not thinking about right now. In my experience maintaining these makefiles since 2012, moving files, or deleting "temporary" files in the build output almost always leads to problems with incremental or interrupted builds. Please leave them be and copy them to where they need to go. Excluding the marker files is certainly a good idea. If this was a review for mainline, I would not accept moving the files, but since this is a project repo, I can assume this is a work in progress and you are free to experiment any which way you like. The final review happens when it goes into mainline.
> 
> Yes, it's correct to not add `$($(MODULE)-$(VALUECLASSES_STR))` to `TARGETS` since it's an intermediate build step. We only need to add targets to `TARGETS` when they are end targets for the makefile.

Okay, cool, I'll switch it to a copy and leave the intermediate marker NOT added to TARGETS.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1949#discussion_r2718608599