[Swan-dev] Relative build paths

[Andrew Cagney]

Something unintentionally changed in my srcdir commit was to change
VPATH to a relative path (As an aside my preference is to push
changes, especially to the build system, early and slowly so that
problems are caught before too big a hole has been dug :-)

It is probably worth explaining a little as to what got changed.

Before this round, generated Makefiles under OBJ looked like:

$ cat OBJ.linux.x86_64/programs/pluto/Makefile
srcdir=/home/cagney/libreswan-master/programs/pluto/
OBJDIR=OBJ.linux.x86_64
OBJDIRTOP=/home/cagney/libreswan-master/OBJ.linux.x86_64
...
LIBRESWANSRCDIR=/home/cagney/libreswan-master
...

they now look like:

$ cat OBJ.linux.x86_64/programs/pluto/Makefile
OBJDIR=OBJ.linux.x86_64
top_builddir=../..
include $(top_builddir)/../Makefile.dirs
SRCDIR=$(abs_srcdir)/
...

notice how everything is relative.  If an absolute path is required it
is computed at runtime by Makefile.dirs (mumble something about
wanting to move Makefile.dirs to mk/dirs.mk :-).

This is a good thing (tm).  Moving things around is no longer a pain.
For instance:

$ ( cd libreswan-master && make programs )
$ mv libreswan-master libreswan-foo
$ ( cd libreswan-foo && make clean )

now does the right thing(tm).

As for relative VPATHs, I didn't notice.  Emacs (and I'd assume any
IDE) happily deal with it.   Debuggers also happily deal with it.   It
even makes debugging a moved build easier.

In the future, want to consider making a relative VPATH an option.

Andrew