1 files changed, 20 insertions, 5 deletions

diff --git a/gl/m4/sys_uio_h.m4 b/gl/m4/sys_uio_h.m4
index c75cbbd..fa176e0 100644
--- a/gl/m4/sys_uio_h.m4
+++ b/gl/m4/sys_uio_h.m4
@@ -1,10 +1,10 @@
-# sys_uio_h.m4 serial 1
-dnl Copyright (C) 2011-2013 Free Software Foundation, Inc.
+# sys_uio_h.m4 serial 3
+dnl Copyright (C) 2011-2021 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.
 
-AC_DEFUN([gl_HEADER_SYS_UIO],
+AC_DEFUN_ONCE([gl_SYS_UIO_H],
 [
   AC_REQUIRE([gl_SYS_UIO_H_DEFAULTS])
   dnl <sys/uio.h> is always overridden, because of GNULIB_POSIXCHECK.
@@ -17,15 +17,30 @@ AC_DEFUN([gl_HEADER_SYS_UIO],
   AC_SUBST([HAVE_SYS_UIO_H])
 ])
 
+# gl_SYS_UIO_MODULE_INDICATOR([modulename])
+# sets the shell variable that indicates the presence of the given module
+# to a C preprocessor expression that will evaluate to 1.
+# This macro invocation must not occur in macros that are AC_REQUIREd.
 AC_DEFUN([gl_SYS_UIO_MODULE_INDICATOR],
 [
-  dnl Use AC_REQUIRE here, so that the default settings are expanded once only.
-  AC_REQUIRE([gl_SYS_UIO_H_DEFAULTS])
+  dnl Ensure to expand the default settings once only.
+  gl_SYS_UIO_H_REQUIRE_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])
 ])
 
+# Initializes the default values for AC_SUBSTed shell variables.
+# This macro must not be AC_REQUIREd.  It must only be invoked, and only
+# outside of macros or in macros that are not AC_REQUIREd.
+AC_DEFUN([gl_SYS_UIO_H_REQUIRE_DEFAULTS],
+[
+  m4_defun(GL_MODULE_INDICATOR_PREFIX[_SYS_UIO_H_MODULE_INDICATOR_DEFAULTS], [
+  ])
+  m4_require(GL_MODULE_INDICATOR_PREFIX[_SYS_UIO_H_MODULE_INDICATOR_DEFAULTS])
+  AC_REQUIRE([gl_SYS_UIO_H_DEFAULTS])
+])
+
 AC_DEFUN([gl_SYS_UIO_H_DEFAULTS],
 [
 ])