absolute-header: Make the macro usable in more situations.

ChangeLog

@@ -1,3 +1,10 @@
+2010-05-16  Bruno Haible  <bruno@clisp.org>
+
+	absolute-header: Make the macro usable in more situations.
+	* m4/absolute-header.m4 (gl_ABSOLUTE_HEADER_ONE): New macro, extracted
+	from gl_ABSOLUTE_HEADER.
+	(gl_ABSOLUTE_HEADER): Use it. Fix comment.
+
 2010-05-16  James Youngman  <jay@gnu.org>
 
 	doc: update users.txt

m4/absolute-header.m4

@@ -1,4 +1,4 @@
-# absolute-header.m4 serial 11
+# absolute-header.m4 serial 12
 dnl Copyright (C) 2006-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -8,7 +8,7 @@ dnl From Derek Price.
 
 # gl_ABSOLUTE_HEADER(HEADER1 HEADER2 ...)
 # ---------------------------------------
-# Find the absolute name of a header file, assuming the header exists.
+# Find the absolute name of a header file, testing first if the header exists.
 # If the header were sys/inttypes.h, this macro would define
 # ABSOLUTE_SYS_INTTYPES_H to the `""' quoted absolute name of sys/inttypes.h
 # in config.h
@@ -31,7 +31,27 @@ m4_foreach_w([gl_HEADER_NAME], [$1],
                     [ac_cv_header_]m4_defn([gl_HEADER_NAME]))dnl
     AC_CHECK_HEADERS_ONCE(m4_defn([gl_HEADER_NAME]))dnl
     if test AS_VAR_GET(ac_header_exists) = yes; then
-      AC_LANG_CONFTEST([AC_LANG_SOURCE([[#include <]]m4_dquote(m4_defn([gl_HEADER_NAME]))[[>]])])
+      gl_ABSOLUTE_HEADER_ONE(m4_defn([gl_HEADER_NAME]))
+    fi
+    AS_VAR_POPDEF([ac_header_exists])dnl
+    ])dnl
+  AC_DEFINE_UNQUOTED(AS_TR_CPP([ABSOLUTE_]m4_defn([gl_HEADER_NAME])),
+                     ["AS_VAR_GET(gl_absolute_header)"],
+                     [Define this to an absolute name of <]m4_defn([gl_HEADER_NAME])[>.])
+  AS_VAR_POPDEF([gl_absolute_header])dnl
+])dnl
+])# gl_ABSOLUTE_HEADER
+
+# gl_ABSOLUTE_HEADER_ONE(HEADER)
+# ------------------------------
+# Like gl_ABSOLUTE_HEADER, except that:
+#   - it assumes that the header exists,
+#   - it uses the current CPPFLAGS,
+#   - it does not cache the result,
+#   - it is silent.
+AC_DEFUN([gl_ABSOLUTE_HEADER_ONE],
+[
+  AC_LANG_CONFTEST([AC_LANG_SOURCE([[#include <]]m4_dquote([$1])[[>]])])
   dnl AIX "xlc -E" and "cc -E" omit #line directives for header files
   dnl that contain only a #include of other header files and no
   dnl non-comment tokens of their own. This leads to a failure to
@@ -46,20 +66,12 @@ m4_foreach_w([gl_HEADER_NAME], [$1],
   dnl eval is necessary to expand gl_absname_cpp.
   dnl Ultrix and Pyramid sh refuse to redirect output of eval,
   dnl so use subshell.
-      AS_VAR_SET(gl_absolute_header,
+  AS_VAR_SET([gl_cv_absolute_]AS_TR_SH([[$1]]),
 [`(eval "$gl_absname_cpp conftest.$ac_ext") 2>&AS_MESSAGE_LOG_FD |
-sed -n '\#/]m4_defn([gl_HEADER_NAME])[#{
+sed -n '\#/$1#{
-        s#.*"\(.*/]m4_defn([gl_HEADER_NAME])[\)".*#\1#
+        s#.*"\(.*/$1\)".*#\1#
         s#^/[^/]#//&#
         p
         q
 }'`])
-    fi
+])
-    AS_VAR_POPDEF([ac_header_exists])dnl
-    ])dnl
-  AC_DEFINE_UNQUOTED(AS_TR_CPP([ABSOLUTE_]m4_defn([gl_HEADER_NAME])),
-                     ["AS_VAR_GET(gl_absolute_header)"],
-                     [Define this to an absolute name of <]m4_defn([gl_HEADER_NAME])[>.])
-  AS_VAR_POPDEF([gl_absolute_header])dnl
-])dnl
-])# gl_ABSOLUTE_HEADER