modernize handling of 'struct utimbuf'

[Bruno Haible]

On Unix systems, there is no problem any more nowadays with 'struct utimbuf':
A web search for "checking for struct utimbuf... no" does not find any
relevant hits in the last 11 years.

On the other hand, there is a problem on native Windows (both mingw and MSVC):
The header file defines 'struct _utimbuf' in this case.

This patch removes the old gl_CHECK_TYPE_STRUCT_UTIMBUF macro and instead
adds the proper support for native Windows.


2017-04-29  Bruno Haible  <address@hidden>

        utime-h: Modernize handling of 'struct utimbuf'.
        * lib/utime.in.h: Include next <utime.h> if it exists.
        (utimbuf): Define to _utimbuf on native Windows.
        * m4/utime_h.m4 (gl_UTIME_H): Check for prerequisites of include_next.
        Set UTIME_H on native Windows.
        (gl_UTIME_MODULE_INDICATOR, gl_HEADER_UTIME_H_DEFAULTS): New macros.
        * modules/utime-h (Depends-on): Add include_next.
        (Makefile.am): Substitute also HAVE_UTIME_H, INCLUDE_NEXT,
        PRAGMA_SYSTEM_HEADER, PRAGMA_COLUMNS, NEXT_UTIME_H.

        * lib/utimens.c (utimbuf): Remove fallback definition.
        * m4/utimens.m4 (gl_UTIMENS): Don't require
        gl_CHECK_TYPE_STRUCT_UTIMBUF.
        * m4/utimbuf.m4: Remove file.
        * modules/utimens (Files): Remove m4/utimbuf.m4.

diff --git a/lib/utime.in.h b/lib/utime.in.h
index 0e3926a..26a1cea 100644
--- a/lib/utime.in.h
+++ b/lib/utime.in.h
@@ -1,4 +1,4 @@
-/* Substitute for <utime.h>
+/* Substitute for and wrapper around <utime.h>.
    Copyright (C) 2017 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
@@ -15,8 +15,31 @@
    along with this program; if not, see <http://www.gnu.org/licenses/>.  */
 
 #ifndef address@hidden@_UTIME_H
+
+#if __GNUC__ >= 3
address@hidden@
+#endif
address@hidden@
+
+/* The include_next requires a split double-inclusion guard.  */
+#if @HAVE_UTIME_H@
+# @INCLUDE_NEXT@ @NEXT_UTIME_H@
+#endif
+
+#ifndef address@hidden@_UTIME_H
 #define address@hidden@_UTIME_H
 
-#include <sys/utime.h>
+#if address@hidden@
+# include <sys/utime.h>
+#endif
 
+#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
+
+/* Define 'struct utimbuf' as an alias of 'struct _utimbuf'
+   (or possibly, if present, 'struct __utimbuf64').  */
+# define utimbuf _utimbuf
+
+#endif
+
+#endif /* address@hidden@_UTIME_H */
 #endif /* address@hidden@_UTIME_H */
diff --git a/lib/utimens.c b/lib/utimens.c
index 5c6e404..3b45119 100644
--- a/lib/utimens.c
+++ b/lib/utimens.c
@@ -35,16 +35,6 @@
 #include "stat-time.h"
 #include "timespec.h"
 
-/* Some systems (even some that do have <utime.h>) don't declare this
-   structure anywhere.  */
-#ifndef HAVE_STRUCT_UTIMBUF
-struct utimbuf
-{
-  long actime;
-  long modtime;
-};
-#endif
-
 /* Avoid recursion with rpl_futimens or rpl_utimensat.  */
 #undef futimens
 #undef utimensat
diff --git a/m4/utimbuf.m4 b/m4/utimbuf.m4
deleted file mode 100644
index 1c42234..0000000
--- a/m4/utimbuf.m4
+++ /dev/null
@@ -1,39 +0,0 @@
-# serial 9
-
-# Copyright (C) 1998-2001, 2003-2004, 2007, 2009-2017 Free Software Foundation,
-# Inc.
-#
-# This file is free software; the Free Software Foundation
-# gives unlimited permission to copy and/or distribute it,
-# with or without modifications, as long as this notice is preserved.
-
-dnl From Jim Meyering
-
-dnl Define HAVE_STRUCT_UTIMBUF if 'struct utimbuf' is declared --
-dnl usually in <utime.h>.
-dnl Some systems have utime.h but don't declare the struct anywhere.
-
-AC_DEFUN([gl_CHECK_TYPE_STRUCT_UTIMBUF],
-[
-  AC_CHECK_HEADERS_ONCE([sys/time.h utime.h])
-  AC_CACHE_CHECK([for struct utimbuf], [gl_cv_sys_struct_utimbuf],
-    [AC_COMPILE_IFELSE(
-       [AC_LANG_PROGRAM(
-          [[#if HAVE_SYS_TIME_H
-             #include <sys/time.h>
-            #endif
-            #include <time.h>
-            #ifdef HAVE_UTIME_H
-             #include <utime.h>
-            #endif
-          ]],
-          [[static struct utimbuf x; x.actime = x.modtime;]])],
-       [gl_cv_sys_struct_utimbuf=yes],
-       [gl_cv_sys_struct_utimbuf=no])])
-
-  if test $gl_cv_sys_struct_utimbuf = yes; then
-    AC_DEFINE([HAVE_STRUCT_UTIMBUF], [1],
-      [Define if struct utimbuf is declared -- usually in <utime.h>.
-       Some systems have utime.h but don't declare the struct anywhere. ])
-  fi
-])
diff --git a/m4/utime_h.m4 b/m4/utime_h.m4
index c29ae42..6b0ac5c 100644
--- a/m4/utime_h.m4
+++ b/m4/utime_h.m4
@@ -8,12 +8,43 @@ dnl From Bruno Haible.
 
 AC_DEFUN([gl_UTIME_H],
 [
-  UTIME_H=''
+  AC_REQUIRE([AC_CANONICAL_HOST])
+  AC_REQUIRE([gl_UTIME_H_DEFAULTS])
   AC_CHECK_HEADERS_ONCE([utime.h])
+  gl_CHECK_NEXT_HEADERS([utime.h])
+
+  if test $ac_cv_header_utime_h = yes; then
+    HAVE_UTIME_H=1
+  else
+    HAVE_UTIME_H=0
+  fi
+  AC_SUBST([HAVE_UTIME_H])
+
+  UTIME_H=''
   if test $ac_cv_header_utime_h != yes; then
     dnl Provide a substitute <utime.h> file.
     UTIME_H=utime.h
+  else
+    case "$host_os" in
+      mingw*) dnl Need special handling of 'struct utimbuf'.
+        UTIME_H=utime.h
+        ;;
+    esac
   fi
   AC_SUBST([UTIME_H])
   AM_CONDITIONAL([GL_GENERATE_UTIME_H], [test -n "$UTIME_H"])
 ])
+
+AC_DEFUN([gl_UTIME_MODULE_INDICATOR],
+[
+  dnl Use AC_REQUIRE here, so that the default settings are expanded once only.
+  AC_REQUIRE([gl_UTIME_H_DEFAULTS])
+  gl_MODULE_INDICATOR_SET_VARIABLE([$1])
+  dnl Define it also as a C macro, for the benefit of the unit tests.
+  gl_MODULE_INDICATOR_FOR_TESTS([$1])
+])
+
+AC_DEFUN([gl_UTIME_H_DEFAULTS],
+[
+  dnl Assume POSIX behavior unless another module says otherwise.
+])
diff --git a/m4/utimens.m4 b/m4/utimens.m4
index c58e93c..f3feab3 100644
--- a/m4/utimens.m4
+++ b/m4/utimens.m4
@@ -3,14 +3,13 @@ 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 serial 7
+dnl serial 8
 
 AC_DEFUN([gl_UTIMENS],
 [
   dnl Prerequisites of lib/utimens.c.
   AC_REQUIRE([gl_FUNC_UTIMES])
   AC_REQUIRE([gl_CHECK_TYPE_STRUCT_TIMESPEC])
-  AC_REQUIRE([gl_CHECK_TYPE_STRUCT_UTIMBUF])
   AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
   AC_CHECK_FUNCS_ONCE([futimes futimesat futimens utimensat lutimes])
 
diff --git a/modules/utime-h b/modules/utime-h
index 6e32c50..0e02d5b 100644
--- a/modules/utime-h
+++ b/modules/utime-h
@@ -6,6 +6,7 @@ lib/utime.in.h
 m4/utime_h.m4
 
 Depends-on:
+include_next
 
 configure.ac:
 gl_UTIME_H
@@ -20,6 +21,11 @@ utime.h: utime.in.h $(top_builddir)/config.status
        $(AM_V_GEN)rm -f address@hidden $@ && \
        { echo '/* DO NOT EDIT! GENERATED AUTOMATICALLY! */' && \
          sed -e 's|@''GUARD_PREFIX''@|${gl_include_guard_prefix}|g' \
+             -e 's/@''HAVE_UTIME_H''@/$(HAVE_UTIME_H)/g' \
+             -e 's|@''INCLUDE_NEXT''@|$(INCLUDE_NEXT)|g' \
+             -e 's|@''PRAGMA_SYSTEM_HEADER''@|@PRAGMA_SYSTEM_HEADER@|g' \
+             -e 's|@''PRAGMA_COLUMNS''@|@PRAGMA_COLUMNS@|g' \
+             -e 's|@''NEXT_UTIME_H''@|$(NEXT_UTIME_H)|g' \
              < $(srcdir)/utime.in.h; \
        } > address@hidden && \
        mv address@hidden $@
diff --git a/modules/utimens b/modules/utimens
index b43872e..c8167ce 100644
--- a/modules/utimens
+++ b/modules/utimens
@@ -4,7 +4,6 @@ Set file access and modification times.
 Files:
 lib/utimens.c
 lib/utimens.h
-m4/utimbuf.m4
 m4/utimens.m4
 m4/utimes.m4