[jdk20] RFR: 8298459: Fix msys2 linking and handling out of tree build directory for source zip creation

[Erik Joelsson]

On Fri, 9 Dec 2022 11:26:46 GMT, Christoph Langer <clanger at openjdk.org> wrote:

> This PR fixes two issues.
> 
> In ZipSource.gmk we don't account for the possibility of the build directory or `$(SUPPORT_OUTPUTDIR)` not being in the source directory tree (`$(TOPDIR)`).
> It doesn't manifest in a build error though since link-file-relative will then fall back to absolute linking. But it results in awkward paths.
> 
> Furthermore, there's a lurking issue in msys2 builds on Windows. There, ln would create deep copies of a file system tree instead of linking. If the file system to be linked contains long paths, it could result in 'File name too long' errors, like can be seen [here](https://github.com/gdams/jdk11u-dev/actions/runs/3563481453/jobs/5986319107). We can avoid this by calling Windows mklink to create a file system junction. Presumably that would also help build performance (though not verified).

make/common/MakeBase.gmk line 319:

> 317: 	else \
> 318: 	  $(LN) -s '$(call DecodeSpace, $(call RelativePath, $<, $(@D)))' '$(call DecodeSpace, $@)'; \
> 319: 	fi

I think it would be better to evaluate this conditional in make rather than the shell. Something like this:
Suggestion:

	ifeq ($(OPENJDK_BUILD_OS_ENV), windows.msys2)
	  cmd //c "mklink /J $(call FixPath, $(call DecodeSpace, $@)) $(call FixPath, $(call DecodeSpace, $<))"
	else
	  $(LN) -s '$(call DecodeSpace, $(call RelativePath, $<, $(@D)))' '$(call DecodeSpace, $@)'
	endif

Just note that the make conditional lines need to be space indented. Same goes for the expression below.

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PR: https://git.openjdk.org/jdk20/pull/9