RFR: 8351029: IncludeCustomExtension does not work on cygwin with source code below /home

[Magnus Ihse Bursie]

On Wed, 7 May 2025 15:08:53 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> If you check out your source code in Cygwin, somewhere under /home/... (as opposed to /cygpath/...), IncludeCustomExtension does not work.
> 
> The problem is that TOPDIR gets a different lexical value from the spec.gmk file when setup in Makefile, even if this was the same directory. Since THIS_INCLUDE is calculated as a relative path by string substitution of $(TOPDIR), the path failed to relativize correctly.

I just realized that it might be possible to pass the TOPDIR actually used down to MakeIncludeStart, and it might be a better solution... I'll check that.

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PR Comment: https://git.openjdk.org/jdk/pull/25100#issuecomment-2860453924