@node ax_extend_srcdir
@unnumberedsec ax_extend_srcdir

@majorheading Synopsis

@smallexample
AX_EXTEND_SRCDIR
@end smallexample

@majorheading Description

The AX_EXTEND_SRCDIR macro extends $srcdir by one path component.

As an example, when working in /home/michael/i3-4.12/build and calling
../configure, your $srcdir is "..". After calling AX_EXTEND_SRCDIR,
$srcdir will be set to "../../i3-4.12".

The result of extending $srcdir is that filenames (e.g. in the output of
the "backtrace" gdb command) will include one more path component of the
absolute source path. The additional path component makes it easy for
users to recognize which files belong to the PACKAGE, and -- provided a
dist tarball was unpacked -- which version of PACKAGE was used.

As an example, in "backtrace", you will see:

@smallexample
  #0  main (argc=1, argv=0x7fffffff1fc8) at ../../i3-4.12/src/main.c:187
@end smallexample

instead of:

@smallexample
  #0  main (argc=1, argv=0x7fffffff1fc8) at ../src/main.c:187
@end smallexample

In case your code uses the __FILE__ preprocessor directive to refer to
the filename of the current source file (e.g. in debug messages), using
the extended path might be undesirable. For this purpose,
AX_EXTEND_SRCDIR defines the output variable AX_EXTEND_SRCDIR_CPPFLAGS,
which can be added to AM_CPPFLAGS in Makefile.am in order to define the
preprocessor directive STRIPPED__FILE__. As an example, when compiling
the file "../../i3-4.12/src/main.c", STRIPPED__FILE__ evaluates to
"main.c".

There are some caveats: When $srcdir is "." (i.e. when ./configure was
called instead of ../configure in a separate build directory),
AX_EXTEND_SRCDIR will still extend $srcdir, but the intended effect will
not be achieved because of the way automake specifies file paths:
automake defines COMPILE to use "`test -f '$source' || echo
'\$(srcdir)/'`$source" in order to prefer files in the current directory
over specifying $srcdir explicitly.

The AX_EXTEND_SRCDIR author is not aware of any way to influence this
automake behavior. Patches very welcome.

To work around this issue, you can use AX_ENABLE_BUILDDIR i.e. by adding
the following code to configure.ac:

@smallexample
  AX_ENABLE_BUILDDIR
  dnl ...
  AX_EXTEND_SRCDIR
@end smallexample

Then also add this bit to Makefile.am (if you wish to use
STRIPPED__FILE__ in your code):

@smallexample
  AM_CPPFLAGS = @@AX_EXTEND_SRCDIR_CPPFLAGS@@
@end smallexample

@majorheading Source Code

Download the
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_extend_srcdir.m4,latest
version of @file{ax_extend_srcdir.m4}} or browse
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=history;f=m4/ax_extend_srcdir.m4,the
macro's revision history}.

@majorheading License

@w{Copyright @copyright{} 2016 Michael Stapelberg @email{michael@@i3wm.org}}

Copying and distribution of this file, with or without modification, are
permitted in any medium without royalty provided the copyright notice
and this notice are preserved.  This file is offered as-is, without any
warranty.