Re: AM_CPPFLAGS best practice

[Jim Meyering]

Eric Blake wrote:

> The manual (gnulib-tool.texi) recommends including both builddir and
> srcdir into AM_CPPFLAGS (aka INCLUDES if you are using automake 1.9),
> which makes sense, since some headers come straight from gnulib and live
> in srcdir, while other headers are generated based on configure results
> and thus live in builddir.  But which order is preferred?
>
> The gnulib manual recommends:
> AM_CPPFLAGS = -I$(top_builddir)/lib -I$(top_srcdir)/lib
>
> But m4 is using the reverse order:
> AM_CPPFLAGS = -I$(top_srcdir)/lib -I../lib
>
> And coreutils has a bug, for forgetting the builddir version (which
> means it will build in an in-tree build, but probably fail in a VPATH
> build):
> AM_CPPFLAGS = -I$(top_srcdir)/lib

"forgetting"? ;-)  Nah.
On the contrary, I vaguely recall deliberately removing the
explicit (and then-redundant) -I... option back when I noticed
that automake handled that part for us.

In the case of coreutils, DEFAULT_INCLUDES covers that:

    $ grep DEFAULT_INCLUDES.= src/Makefile
    DEFAULT_INCLUDES = -I. -I$(top_builddir)/lib

>From what I recall, that's by virtue of our putting config.h in lib
via this line from configure.ac:

    AC_CONFIG_HEADERS([lib/config.h:lib/config.hin])

Of course, if something uses $(AM_CPPFLAGS) without also
using $(DEFAULT_INCLUDES), then you'd have a point.