largefile: sync from Autoconf master

* modules/largefile-required, modules/year2038-required: New modules.
* MODULES.html.sh, doc/largefile.texi, doc/posix-headers/time.texi:
* doc/year2038.texi: Document this.
* m4/largefile.m4: Sync from Autoconf master.
Conditionalize the workaround on AC_SYS_LARGEFILE_REQUIRED rather
than on AC_SYS_YEAR2038 so that we replace older but still
unreleased Autoconf.
(AC_SYS_LARGEFILE_REQUIRED, AC_SYS_YEAR2038_REQUIRED): New macros.

8 files changed, 195 insertions, 65 deletions

diff --git a/ChangeLog b/ChangeLog
index bb49b16cf0..05b11d9f50 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2023-04-09  Paul Eggert  <eggert@cs.ucla.edu>
 
+	largefile: sync from Autoconf master
+	* m4/largefile.m4 (_AC_SYS_LARGEFILE_TEST_INCLUDES):
+	Now an alias for _AC_SYS_LARGEFILE_TEST_CODE.
+	(AC_SYS_LARGEFILE_REQUIRED, AC_SYS_YEAR2038_REQUIRED): New macros.
+
 	year2038: configure earlier
 	* modules/year2038: Put AC_SYS_YEAR2038 in configure.ac-early
 	since it can affect CPPFLAGS with _TIME_BITS=64.
diff --git a/MODULES.html.sh b/MODULES.html.sh
index 714aedd308..2eeffb690f 100755
--- a/MODULES.html.sh
+++ b/MODULES.html.sh
@@ -1733,6 +1733,7 @@ func_all_modules ()
   func_module time-h
   func_module time_rz
   func_module year2038
+  func_module year2038-required
   func_end_table
 
   element="Extra functions based on ANSI C 89"
@@ -2781,6 +2782,7 @@ func_all_modules ()
   func_module fts
   func_module isdir
   func_module largefile
+  func_module largefile-required
   func_module lchmod
   func_module lchown
   func_module mkancesdirs
diff --git a/doc/largefile.texi b/doc/largefile.texi
index 13572b47e5..b5bfa5116a 100644
--- a/doc/largefile.texi
+++ b/doc/largefile.texi
@@ -1,9 +1,22 @@
 @node Large File Support
 @section Large File Support
 
-The module provides support for files larger than 2 GB, or with device
-or inode numbers or timestamps exceeding 32 bits.  To this effect, it
-ensures that types like @code{off_t} and @code{time_t} are 64-bit when possible,
+The Gnulib @samp{largefile-required} module provides support for files
+2 GiB and larger, or with device or inode numbers exceeding 32 bits.
+To this effect, it ensures that types like @code{off_t} and
+@code{ino_t} are 64-bit,
 at least on the following platforms:
 glibc, Mac OS X, FreeBSD, NetBSD, OpenBSD, AIX, HP-UX, IRIX, Solaris,
 Cygwin, mingw, MSVC.
+
+The Gnulib @samp{largefile} module is similar, except that it gives
+@command{configure} an option @samp{--disable-largefile} that
+suppresses support for large files.  This may be useful if the package
+links to other libraries whose user-facing ABIs still require
+@code{off_t} or most other file-related types to be 32-bit on your
+platform.
+
+Both modules also add to @command{configure} an option
+@code{--enable-year2038}, needed on some platforms to access files
+with timestamps past the year 2038.  @xref{Avoiding the year 2038
+problem}.
diff --git a/doc/posix-headers/time.texi b/doc/posix-headers/time.texi
index 5ecebbfdda..a506ec640c 100644
--- a/doc/posix-headers/time.texi
+++ b/doc/posix-headers/time.texi
@@ -18,14 +18,16 @@ expressions:
 NetBSD 5.0.
 @end itemize
 
-Portability problems fixed by the Gnulib module @code{year2038}:
+Portability problems fixed by the Gnulib modules
+@code{year2038-required} and @code{year-2038}:
 @itemize
 @item
 On some platforms where @code{time_t} defaults to 32-bit but can be
 changed to 64-bit, functions like @code{stat} can fail with
 @code{errno == EOVERFLOW} when a 32-bit timestamp is out of range,
 such as with a file timestamp in the far future or past:
-glibc 2.34.
+glibc 2.34+ atop 32-bit x86 or ARM Linux.
+@xref{Avoiding the year 2038 problem}.
 @end itemize
 
 Portability problems not fixed by Gnulib:
@@ -39,6 +41,8 @@ the functions silently return the low-order 32 bits of the correct
 timestamp.  These platforms will be obsolete when 32-bit @code{time_t}
 rolls around, which will occur in 2038 for the typical case when
 @code{time_t} is signed.
+@xref{Avoiding the year 2038 problem}.
+
 @item
 On some platforms the @code{tv_nsec} member of @code{struct timespec}
 is not of type @code{long}, but is of type @code{long long} instead:
diff --git a/doc/year2038.texi b/doc/year2038.texi
index 213fda235f..d98753101e 100644
--- a/doc/year2038.texi
+++ b/doc/year2038.texi
@@ -1,25 +1,43 @@
 @node Avoiding the year 2038 problem
 @section Avoiding the year 2038 problem
 
-The ``year 2038 problem'' denotes unpredictable behaviour of programs
-that will likely occur in the year 2038, for programs that use a 32-bit
-@samp{time_t} type.  See @url{https://en.wikipedia.org/wiki/Year_2038_problem}
-for details.
+The ``year 2038 problem'' denotes unpredictable behaviour that will
+likely occur in the year 2038, for programs that use a 32-bit signed
+integer @samp{time_t} type that cannot represent timestamps on or
+after 2038-01-19 03:14:08 UTC@.  See
+@url{https://en.wikipedia.org/wiki/Year_2038_problem, Year 2038
+problem} for details.
 
-The Gnulib module @samp{year2038} attempts to avoid this problem, by
-ensuring that @code{time_t} is a 64-bit type and by causing
-@code{configure} to fail otherwise.
+The Gnulib module @samp{year2038-required} fixes this problem, by
+making @code{time_t} wide enough to represent timestamps after 2038.
+This has no effect on most current systems, which have timestamps that
+are already wide enough.  However, @samp{year2038-required} arranges
+for builds on legacy 32-bit x86 and ARM Linux kernels running glibc
+2.34 and later to compile with @samp{_TIME_BITS=64} to get wider
+timestamps.  On older platforms that do not support timestamps after
+the year 2038, @samp{year2038-required} causes @command{configure} to
+fail.
 
-The Gnulib module @samp{largefile} also attempts to avoid this problem
-when possible, because @samp{largefile} enables the widest
-file-related types supported by the system and @code{time_t} is one of
-those types.  However, @code{largefile} does not cause
-@code{configure} to fail when the year 2038 problem is not avoidable.
+The Gnulib module @samp{year2038} is like @samp{year2038-required},
+except that it causes @command{configure} to fail only when it appears
+that the current system should support post-2038 timestamps but
+something prevents that from working.  Also, @samp{year2038} gives
+@command{configure} a @option{--disable-year2038} option, which
+suppresses support for post-2038 timestamps.  This may be useful if
+the package links to other libraries whose user-facing ABIs still
+require @code{time_t} to be 32-bit on your platform.
 
-The Gnulib @samp{largefile} and @samp{year2038} modules are
+The Gnulib module @samp{year2038-required} is
 recommended for any package that might be used after the year 2038 on
-32-bit platforms.  However, if you build such a package you can
-disable its use of 64-bit @code{time_t} by giving the
-@code{--disable-year2038} option to @code{configure}.  This may be
-useful if the package links to other libraries whose user-facing ABIs
-still require @code{time_t} to be 32-bit on your platform.
+32-bit platforms.  However, if your package needs to support
+platforms that will not be used after the year 2038,
+you can use the @samp{year2038} module instead.
+
+If the Gnulib module @samp{largefile} is used but neither
+@samp{year2038} nor @samp{year2038-required} is used,
+@command{configure} will have an option @option{--enable-year2038}
+that causes @code{configure} to behave as if @samp{year2038} was used.
+This is for packages that have long used @samp{largefile} but have not
+gotten around to upgrade their Gnulib module list to include
+@samp{year2038-required} or @samp{year2038}.
+@xref{Large File Support}.
diff --git a/m4/largefile.m4 b/m4/largefile.m4
index b128e24353..4bfff0d076 100644
--- a/m4/largefile.m4
+++ b/m4/largefile.m4
@@ -24,29 +24,9 @@ AC_DEFUN([gl_SET_LARGEFILE_SOURCE],
  ]])
 )
 
-# Work around a problem in autoconf <= 2.69:
-# AC_SYS_LARGEFILE does not configure for large inodes on Mac OS X 10.5,
-# or configures them incorrectly in some cases.
-m4_version_prereq([2.70], [], [
-
-# _AC_SYS_LARGEFILE_TEST_INCLUDES
-# -------------------------------
-m4_define([_AC_SYS_LARGEFILE_TEST_INCLUDES],
-[#include <sys/types.h>
- /* Check that off_t can represent 2**63 - 1 correctly.
-    We can't simply define LARGE_OFF_T to be 9223372036854775807,
-    since some C++ compilers masquerading as C compilers
-    incorrectly reject 9223372036854775807.  */
-#define LARGE_OFF_T (((off_t) 1 << 31 << 31) - 1 + ((off_t) 1 << 31 << 31))
-  int off_t_is_large[[(LARGE_OFF_T % 2147483629 == 721
-                       && LARGE_OFF_T % 2147483647 == 1)
-                      ? 1 : -1]];[]dnl
-])
-])# m4_version_prereq 2.70
-
-# Support AC_SYS_YEAR2038, even if Autoconf 2.71 or earlier.
-# This code is taken from Autoconf master.
-m4_ifndef([AC_SYS_YEAR2038], [
+m4_ifndef([AC_SYS_LARGEFILE_REQUIRED], [
+# Support AC_SYS_LARGEFILE_REQUIRED and Y2038 macros, even if
+# Autoconf 2.71 or earlier.  This code is taken from Autoconf master.
 
 # _AC_SYS_YEAR2038_TEST_CODE
 # --------------------------
@@ -118,8 +98,10 @@ AS_CASE([$ac_cv_sys_year2038_opts],
   ["none needed"], [],
   ["support not detected"],
     [ac_have_year2038=no
-     AS_CASE([$enable_year2038],
-      [yes],
+     AS_CASE([$ac_year2038_required,$enable_year2038],
+      [yes,*],
+        [AC_MSG_FAILURE([support for timestamps after Jan 2038 is required])],
+      [*,yes],
         [# If we're not cross compiling and 'touch' works with a large
         # timestamp, then we can presume the system supports wider time_t
         # *somehow* and we just weren't able to detect it.  One common
@@ -165,19 +147,24 @@ AS_CASE([$ac_cv_sys_year2038_opts],
 # --enable-year2038, or a --disable-year2038, or no option at all to
 # the configure script.  Note that this is expanded very late and
 # therefore there cannot be any code in the AC_ARG_ENABLE.  The
-# default value for enable_year2038 is emitted unconditionally
+# default value for 'enable_year2038' is emitted unconditionally
 # because the generated code always looks at this variable.
 m4_define([_AC_SYS_YEAR2038_ENABLE],
 [m4_divert_text([DEFAULTS],
+  m4_provide_if([AC_SYS_YEAR2038_REQUIRED],
+    [ac_year2038_required=yes],
+    [ac_year2038_required=no]))dnl
+m4_divert_text([DEFAULTS],
   m4_provide_if([AC_SYS_YEAR2038],
     [enable_year2038=yes],
     [enable_year2038=no]))]dnl
+[m4_provide_if([AC_SYS_YEAR2038_REQUIRED], [],
 [AC_ARG_ENABLE([year2038],
   m4_provide_if([AC_SYS_YEAR2038],
     [AS_HELP_STRING([--disable-year2038],
-      [do not support timestamps after 2038])],
+      [omit support for dates after Jan 2038])],
     [AS_HELP_STRING([--enable-year2038],
-      [support timestamps after 2038])]))])
+      [include support for dates after Jan 2038])]))])])
 
 # _AC_SYS_YEAR2038_OPT_IN
 # -----------------------
@@ -189,7 +176,8 @@ m4_define([_AC_SYS_YEAR2038_ENABLE],
 # documented macro.
 AC_DEFUN([_AC_SYS_YEAR2038_OPT_IN],
 [m4_provide_if([_AC_SYS_YEAR2038_PROBE], [], [dnl
-  AS_IF([test "$enable_year2038" != no], [_AC_SYS_YEAR2038_PROBE])
+  AS_IF([test "$ac_year2038_required,$enable_year2038" != no,no],
+    [_AC_SYS_YEAR2038_PROBE])
   AC_CONFIG_COMMANDS_PRE([_AC_SYS_YEAR2038_ENABLE])
 ])])
 
@@ -199,9 +187,26 @@ AC_DEFUN([_AC_SYS_YEAR2038_OPT_IN],
 # On systems where time_t is not always 64 bits, this probe can be
 # skipped by passing the --disable-year2038 option to configure.
 AC_DEFUN([AC_SYS_YEAR2038],
-[AC_REQUIRE([AC_SYS_LARGEFILE])]dnl
+[m4_provide_if([AC_SYS_LARGEFILE_REQUIRED], [],
+  [AC_REQUIRE([AC_SYS_LARGEFILE])])]dnl
+[m4_provide_if([_AC_SYS_YEAR2038_PROBE], [], [dnl
+  AS_IF([test "$ac_year2038_required,$enable_year2038" != no,no],
+    [_AC_SYS_YEAR2038_PROBE])
+  AC_CONFIG_COMMANDS_PRE([_AC_SYS_YEAR2038_ENABLE])
+])])
+
+# AC_SYS_YEAR2038_REQUIRED
+# ------------------------
+# Same as AC_SYS_YEAR2038, but declares that this program *requires*
+# support for large time_t.  If we cannot find any way to make time_t
+# capable of representing values larger than 2**31 - 1, configure will
+# error out.  Furthermore, no --enable-year2038 nor --disable-year2038
+# option will be available.
+AC_DEFUN([AC_SYS_YEAR2038_REQUIRED],
+[m4_provide_if([AC_SYS_LARGEFILE_REQUIRED], [],
+  [AC_REQUIRE([AC_SYS_LARGEFILE])])]dnl
 [m4_provide_if([_AC_SYS_YEAR2038_PROBE], [], [dnl
-  AS_IF([test "$enable_year2038" != no], [_AC_SYS_YEAR2038_PROBE])
+  _AC_SYS_YEAR2038_PROBE
   AC_CONFIG_COMMANDS_PRE([_AC_SYS_YEAR2038_ENABLE])
 ])])
 
@@ -219,6 +224,8 @@ m4_define([_AC_SYS_LARGEFILE_TEST_CODE],
 		       && LARGE_OFF_T % 2147483647 == 1)
 		      ? 1 : -1]];[]dnl
 ])
+# Defined by Autoconf 2.71 and circa 2022 Gnulib unwisely depended on it.
+m4_define([_AC_SYS_LARGEFILE_TEST_INCLUDES], [_AC_SYS_LARGEFILE_TEST_CODE])
 
 # _AC_SYS_LARGEFILE_OPTIONS
 # -------------------------
@@ -228,8 +235,8 @@ m4_define([_AC_SYS_LARGEFILE_TEST_CODE],
 m4_define([_AC_SYS_LARGEFILE_OPTIONS], m4_normalize(
     ["none needed"]                   dnl Most current systems
     ["-D_FILE_OFFSET_BITS=64"]        dnl X/Open LFS spec
-    ["-D_LARGE_FILES=1"]              dnl AIX (which versions?)
-    ["-n32"]                          dnl Irix 6.2 w/ SGI compiler
+    ["-D_LARGE_FILES=1"]              dnl 32-bit AIX 4.2.1+, 32-bit z/OS
+    ["-n32"]                          dnl 32-bit IRIX 6, SGI cc (obsolete)
 ))
 
 # _AC_SYS_LARGEFILE_PROBE
@@ -265,7 +272,9 @@ ac_have_largefile=yes
 AS_CASE([$ac_cv_sys_largefile_opts],
   ["none needed"], [],
   ["support not detected"],
-    [ac_have_largefile=no],
+    [ac_have_largefile=no
+     AS_IF([test $ac_largefile_required,$ac_year2038_required != no,no],
+       [AC_MSG_FAILURE([support for large files is required])])],
 
   ["-D_FILE_OFFSET_BITS=64"],
     [AC_DEFINE([_FILE_OFFSET_BITS], [64],
@@ -286,16 +295,25 @@ _AC_SYS_YEAR2038_OPT_IN
 
 # _AC_SYS_LARGEFILE_ENABLE
 # ------------------------
-# Subroutine of AC_SYS_LARGEFILE.  Note that this
+# Subroutine of AC_SYS_LARGEFILE.  If AC_SYS_LARGEFILE_REQUIRED was
+# not used at any point in this configure script, add a
+# --disable-largefile option to the configure script.  Note that this
 # is expanded very late and therefore there cannot be any code in the
-# AC_ARG_ENABLE.  The default value for enable_largefile is emitted
+# AC_ARG_ENABLE.  The default value for 'enable_largefile' is emitted
 # unconditionally because the generated shell code always looks at
 # this variable.
 m4_define([_AC_SYS_LARGEFILE_ENABLE],
 [m4_divert_text([DEFAULTS],
-  enable_largefile=yes)]dnl
-[AC_ARG_ENABLE([largefile],
-  [AS_HELP_STRING([--disable-largefile], [omit support for large files])])])
+  m4_provide_if([AC_SYS_LARGEFILE_REQUIRED],
+    [ac_largefile_required=yes],
+    [ac_largefile_required=no]))dnl
+m4_divert_text([DEFAULTS],
+  [enable_largefile=yes])]dnl
+[m4_provide_if([AC_SYS_LARGEFILE_REQUIRED], [],
+   [m4_provide_if([AC_SYS_YEAR2038_REQUIRED], [],
+      [AC_ARG_ENABLE([largefile],
+         [AS_HELP_STRING([--disable-largefile],
+	    [omit support for large files])])])])])
 
 # AC_SYS_LARGEFILE
 # ----------------
@@ -307,13 +325,29 @@ m4_define([_AC_SYS_LARGEFILE_ENABLE],
 # to have a 64-bit inode number cannot be accessed by 32-bit applications on
 # Linux x86/x86_64.  This can occur with file systems such as XFS and NFS.
 # This macro allows configuration to continue if the system doesn't support
-# large files.
+# large files; see also AC_SYS_LARGEFILE_REQUIRED.
 AC_DEFUN([AC_SYS_LARGEFILE],
 [m4_provide_if([_AC_SYS_LARGEFILE_PROBE], [], [dnl
-  AS_IF([test "$enable_largefile" != no], [_AC_SYS_LARGEFILE_PROBE])
+  AS_IF([test "$ac_largefile_required,$enable_largefile,$ac_year2038_required" != no,no,no],
+    [_AC_SYS_LARGEFILE_PROBE])
+  AC_CONFIG_COMMANDS_PRE([_AC_SYS_LARGEFILE_ENABLE])
+])])
+
+# AC_SYS_LARGEFILE_REQUIRED
+# -------------------------
+# Same as AC_SYS_LARGEFILE, but declares that this program *requires*
+# support for large files.  If we cannot find a combination of compiler
+# options and #defines that makes 'off_t' capable of representing 2**63 - 1,
+# 'configure' will error out.  Furthermore, 'configure' will not offer a
+# --disable-largefile command line option.
+# If both AC_SYS_LARGEFILE and AC_SYS_LARGEFILE_REQUIRED are used in the
+# same configure script -- in either order -- AC_SYS_LARGEFILE_REQUIRED wins.
+AC_DEFUN([AC_SYS_LARGEFILE_REQUIRED],
+[m4_provide_if([_AC_SYS_LARGEFILE_PROBE], [], [dnl
+  _AC_SYS_LARGEFILE_PROBE
   AC_CONFIG_COMMANDS_PRE([_AC_SYS_LARGEFILE_ENABLE])
 ])])
-])# m4_ifndef AC_SYS_YEAR2038
+])# m4_ifndef AC_SYS_LARGEFILE_REQUIRED
 
 # Enable large files on systems where this is implemented by Gnulib, not by the
 # system headers.
diff --git a/modules/largefile-required b/modules/largefile-required
new file mode 100644
index 0000000000..eea5ecf4fc
--- /dev/null
+++ b/modules/largefile-required
@@ -0,0 +1,28 @@
+Description:
+Require support for files 2 GiB and larger.
+
+Comment:
+This module should not be used as a dependency from a test module,
+otherwise when this module occurs as a tests-related module, it will
+have side effects on the compilation of the main modules in lib/.
+
+Files:
+m4/largefile.m4
+
+Depends-on:
+largefile
+
+configure.ac:
+AC_REQUIRE([AC_SYS_LARGEFILE_REQUIRED])
+
+configure.ac:
+
+Makefile.am:
+
+Include:
+
+License:
+LGPLv2+
+
+Maintainer:
+all
diff --git a/modules/year2038-required b/modules/year2038-required
new file mode 100644
index 0000000000..29dd556410
--- /dev/null
+++ b/modules/year2038-required
@@ -0,0 +1,26 @@
+Description:
+Ensure that 'time_t' can go past the year 2038.
+
+Comment:
+This module should not be used as a dependency from a test module,
+otherwise when this module occurs as a tests-related module, it will
+have side effects on the compilation of the main modules in lib/.
+
+Files:
+m4/largefile.m4
+
+Depends-on:
+largefile-required
+
+configure.ac-early:
+AC_REQUIRE([AC_SYS_YEAR2038_REQUIRED])
+
+Makefile.am:
+
+Include:
+
+License:
+LGPLv2+
+
+Maintainer:
+all