# include_next.m4 serial 7
dnl Copyright (C) 2006-2008 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

dnl From Paul Eggert and Derek Price.

dnl Sets INCLUDE_NEXT and PRAGMA_SYSTEM_HEADER.
dnl
dnl INCLUDE_NEXT expands to 'include_next' if the compiler supports it, or to
dnl 'include' otherwise.
dnl
dnl PRAGMA_SYSTEM_HEADER can be used in files that contain #include_next,
dnl so as to avoid GCC warnings when the gcc option -pedantic is used.
dnl '#pragma GCC system_header' has the same effect as if the file was found
dnl through the include search path specified with '-isystem' options (as
dnl opposed to the search path specified with '-I' options). Namely, gcc
dnl does not warn about some things, and on some systems (Solaris and Interix)
dnl __STDC__ evaluates to 0 instead of to 1. The latter is an undesired side
dnl effect; we are therefore careful to use 'defined __STDC__' or '1' instead
dnl of plain '__STDC__'.

AC_DEFUN([gl_INCLUDE_NEXT],
[
  AC_LANG_PREPROC_REQUIRE()
  AC_CACHE_CHECK([whether the preprocessor supports include_next],
    [gl_cv_have_include_next],
    [rm -rf conftestd1 conftestd2
     mkdir conftestd1 conftestd2
     cat <<EOF > conftestd1/conftest.h
#define DEFINED_IN_CONFTESTD1
#include_next <conftest.h>
#ifdef DEFINED_IN_CONFTESTD2
int foo;
#else
#error "include_next doesn't work"
#endif
EOF
     cat <<EOF > conftestd2/conftest.h
#ifndef DEFINED_IN_CONFTESTD1
#error "include_next test doesn't work"
#endif
#define DEFINED_IN_CONFTESTD2
EOF
     save_CPPFLAGS="$CPPFLAGS"
     CPPFLAGS="$CPPFLAGS -Iconftestd1 -Iconftestd2"
     AC_COMPILE_IFELSE([#include <conftest.h>],
       [gl_cv_have_include_next=yes],
       [gl_cv_have_include_next=no])
     CPPFLAGS="$save_CPPFLAGS"
     rm -rf conftestd1 conftestd2
    ])
  PRAGMA_SYSTEM_HEADER=
  if test $gl_cv_have_include_next = yes; then
    INCLUDE_NEXT=include_next
    if test -n "$GCC"; then
      PRAGMA_SYSTEM_HEADER='#pragma GCC system_header'
    fi
  else
    INCLUDE_NEXT=include
  fi
  AC_SUBST([INCLUDE_NEXT])
  AC_SUBST([PRAGMA_SYSTEM_HEADER])
])

# gl_CHECK_NEXT_HEADERS(HEADER1 HEADER2 ...)
# ------------------------------------------
# For each arg foo.h, if #include_next works, define NEXT_FOO_H to be
# '<foo.h>'; otherwise define it to be
# '"///usr/include/foo.h"', or whatever other absolute file name is suitable.
# That way, a header file with the following line:
#	#@INCLUDE_NEXT@ @NEXT_FOO_H@
# behaves (after sed substitution) as if it contained
#	#include_next <foo.h>
# even if the compiler does not support include_next.
# The three "///" are to pacify Sun C 5.8, which otherwise would say
# "warning: #include of /usr/include/... may be non-portable".
# Use `""', not `<>', so that the /// cannot be confused with a C99 comment.
# Note: This macro assumes that the header file is not empty after
# preprocessing, i.e. it does not only define preprocessor macros but also
# provides some type/enum definitions or function/variable declarations.
AC_DEFUN([gl_CHECK_NEXT_HEADERS],
[
  AC_REQUIRE([gl_INCLUDE_NEXT])
  AC_CHECK_HEADERS_ONCE([$1])

  m4_foreach_w([gl_HEADER_NAME], [$1],
    [AS_VAR_PUSHDEF([gl_next_header],
		    [gl_cv_next_]m4_quote(m4_defn([gl_HEADER_NAME])))
     if test $gl_cv_have_include_next = yes; then
       AS_VAR_SET([gl_next_header], ['<'gl_HEADER_NAME'>'])
     else
       AC_CACHE_CHECK(
	 [absolute name of <]m4_quote(m4_defn([gl_HEADER_NAME]))[>],
	 m4_quote(m4_defn([gl_next_header])),
	 [AS_VAR_PUSHDEF([gl_header_exists],
			 [ac_cv_header_]m4_quote(m4_defn([gl_HEADER_NAME])))
	  if test AS_VAR_GET(gl_header_exists) = yes; then
	    AC_LANG_CONFTEST(
	      [AC_LANG_SOURCE(
		 [[#include <]]m4_dquote(m4_defn([gl_HEADER_NAME]))[[>]]
	       )])
	    dnl eval is necessary to expand ac_cpp.
	    dnl Ultrix and Pyramid sh refuse to redirect output of eval,
	    dnl so use subshell.
	    AS_VAR_SET([gl_next_header],
	      ['"'`(eval "$ac_cpp conftest.$ac_ext") 2>&AS_MESSAGE_LOG_FD |
	       sed -n '\#/]m4_quote(m4_defn([gl_HEADER_NAME]))[#{
		 s#.*"\(.*/]m4_quote(m4_defn([gl_HEADER_NAME]))[\)".*#\1#
		 s#^/[^/]#//&#
		 p
		 q
	       }'`'"'])
	  else
	    AS_VAR_SET([gl_next_header], ['<'gl_HEADER_NAME'>'])
	  fi
	  AS_VAR_POPDEF([gl_header_exists])])
     fi
     AC_SUBST(
       AS_TR_CPP([NEXT_]m4_quote(m4_defn([gl_HEADER_NAME]))),
       [AS_VAR_GET([gl_next_header])])
     AS_VAR_POPDEF([gl_next_header])])
])