m4/include_next.m4

   1 # include_next.m4 serial 7
   2 dnl Copyright (C) 2006-2008 Free Software Foundation, Inc.
   3 dnl This file is free software; the Free Software Foundation
   4 dnl gives unlimited permission to copy and/or distribute it,
   5 dnl with or without modifications, as long as this notice is preserved.
   6
   7 dnl From Paul Eggert and Derek Price.
   8
   9 dnl Sets INCLUDE_NEXT and PRAGMA_SYSTEM_HEADER.
  10 dnl
  11 dnl INCLUDE_NEXT expands to 'include_next' if the compiler supports it, or to
  12 dnl 'include' otherwise.
  13 dnl
  14 dnl PRAGMA_SYSTEM_HEADER can be used in files that contain #include_next,
  15 dnl so as to avoid GCC warnings when the gcc option -pedantic is used.
  16 dnl '#pragma GCC system_header' has the same effect as if the file was found
  17 dnl through the include search path specified with '-isystem' options (as
  18 dnl opposed to the search path specified with '-I' options). Namely, gcc
  19 dnl does not warn about some things, and on some systems (Solaris and Interix)
  20 dnl __STDC__ evaluates to 0 instead of to 1. The latter is an undesired side
  21 dnl effect; we are therefore careful to use 'defined __STDC__' or '1' instead
  22 dnl of plain '__STDC__'.
  23
  24 AC_DEFUN([gl_INCLUDE_NEXT],
  25 [
  26   AC_LANG_PREPROC_REQUIRE()
  27   AC_CACHE_CHECK([whether the preprocessor supports include_next],
  28     [gl_cv_have_include_next],
  29     [rm -rf conftestd1 conftestd2
  30      mkdir conftestd1 conftestd2
  31      cat <<EOF > conftestd1/conftest.h
  32 #define DEFINED_IN_CONFTESTD1
  33 #include_next <conftest.h>
  34 #ifdef DEFINED_IN_CONFTESTD2
  35 int foo;
  36 #else
  37 #error "include_next doesn't work"
  38 #endif
  39 EOF
  40      cat <<EOF > conftestd2/conftest.h
  41 #ifndef DEFINED_IN_CONFTESTD1
  42 #error "include_next test doesn't work"
  43 #endif
  44 #define DEFINED_IN_CONFTESTD2
  45 EOF
  46      save_CPPFLAGS="$CPPFLAGS"
  47      CPPFLAGS="$CPPFLAGS -Iconftestd1 -Iconftestd2"
  48      AC_COMPILE_IFELSE([#include <conftest.h>],
  49        [gl_cv_have_include_next=yes],
  50        [gl_cv_have_include_next=no])
  51      CPPFLAGS="$save_CPPFLAGS"
  52      rm -rf conftestd1 conftestd2
  53     ])
  54   PRAGMA_SYSTEM_HEADER=
  55   if test $gl_cv_have_include_next = yes; then
  56     INCLUDE_NEXT=include_next
  57     if test -n "$GCC"; then
  58       PRAGMA_SYSTEM_HEADER='#pragma GCC system_header'
  59     fi
  60   else
  61     INCLUDE_NEXT=include
  62   fi
  63   AC_SUBST([INCLUDE_NEXT])
  64   AC_SUBST([PRAGMA_SYSTEM_HEADER])
  65 ])
  66
  67 # gl_CHECK_NEXT_HEADERS(HEADER1 HEADER2 ...)
  68 # ------------------------------------------
  69 # For each arg foo.h, if #include_next works, define NEXT_FOO_H to be
  70 # '<foo.h>'; otherwise define it to be
  71 # '"///usr/include/foo.h"', or whatever other absolute file name is suitable.
  72 # That way, a header file with the following line:
  73 #       #@INCLUDE_NEXT@ @NEXT_FOO_H@
  74 # behaves (after sed substitution) as if it contained
  75 #       #include_next <foo.h>
  76 # even if the compiler does not support include_next.
  77 # The three "///" are to pacify Sun C 5.8, which otherwise would say
  78 # "warning: #include of /usr/include/... may be non-portable".
  79 # Use `""', not `<>', so that the /// cannot be confused with a C99 comment.
  80 # Note: This macro assumes that the header file is not empty after
  81 # preprocessing, i.e. it does not only define preprocessor macros but also
  82 # provides some type/enum definitions or function/variable declarations.
  83 AC_DEFUN([gl_CHECK_NEXT_HEADERS],
  84 [
  85   AC_REQUIRE([gl_INCLUDE_NEXT])
  86   AC_CHECK_HEADERS_ONCE([$1])
  87
  88   m4_foreach_w([gl_HEADER_NAME], [$1],
  89     [AS_VAR_PUSHDEF([gl_next_header],
  90                     [gl_cv_next_]m4_quote(m4_defn([gl_HEADER_NAME])))
  91      if test $gl_cv_have_include_next = yes; then
  92        AS_VAR_SET([gl_next_header], ['<'gl_HEADER_NAME'>'])
  93      else
  94        AC_CACHE_CHECK(
  95          [absolute name of <]m4_quote(m4_defn([gl_HEADER_NAME]))[>],
  96          m4_quote(m4_defn([gl_next_header])),
  97          [AS_VAR_PUSHDEF([gl_header_exists],
  98                          [ac_cv_header_]m4_quote(m4_defn([gl_HEADER_NAME])))
  99           if test AS_VAR_GET(gl_header_exists) = yes; then
 100             AC_LANG_CONFTEST(
 101               [AC_LANG_SOURCE(
 102                  [[#include <]]m4_dquote(m4_defn([gl_HEADER_NAME]))[[>]]
 103                )])
 104             dnl eval is necessary to expand ac_cpp.
 105             dnl Ultrix and Pyramid sh refuse to redirect output of eval,
 106             dnl so use subshell.
 107             AS_VAR_SET([gl_next_header],
 108               ['"'`(eval "$ac_cpp conftest.$ac_ext") 2>&AS_MESSAGE_LOG_FD |
 109                sed -n '\#/]m4_quote(m4_defn([gl_HEADER_NAME]))[#{
 110                  s#.*"\(.*/]m4_quote(m4_defn([gl_HEADER_NAME]))[\)".*#\1#
 111                  s#^/[^/]#//&#
 112                  p
 113                  q
 114                }'`'"'])
 115           else
 116             AS_VAR_SET([gl_next_header], ['<'gl_HEADER_NAME'>'])
 117           fi
 118           AS_VAR_POPDEF([gl_header_exists])])
 119      fi
 120      AC_SUBST(
 121        AS_TR_CPP([NEXT_]m4_quote(m4_defn([gl_HEADER_NAME]))),
 122        [AS_VAR_GET([gl_next_header])])
 123      AS_VAR_POPDEF([gl_next_header])])
 124 ])