warn-on-use: new module The goal of GNULIB_POSIXCHECK is to allow a developer on a reasonably portable system to detect instances where they may have succeeded because their system is up-to-date, but where compilation would fail or create a misbehaving application on some other system due to some portability problem, all without requiring that the developer have access to other machines. In other words, we want to poison all interfaces that have a gnulib replacement if the corresponding gnulib module is not in use. For macros, the solution is undefining the macro; unfortunately this causes compilation error without many details as to why, but it is better than nothing. For functions, the solution is to cause a warning if the function is used. Previously, the link-warning could poison functions, but only on glibc systems and with gcc. This module introduces _GL_WARN_ON_USE as a way of poisoning functions for a few more systems. Using the gcc __warning__ attribute (added in 4.3.0, early 2008) rather than using link-warning.h is favorable because: 1) Provides a warning immediately at compile-time. The user does not have to wait until he links a program. 2) Less use of C macros. Less risk of collision. 3) It's available on more platforms. Depends only on GCC. 4) The formatting of the message is nicer. There is a minor regression: the gcc attribute is currently not as powerful as a link warning at detecting uses via function pointers: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42384 However, that style of coding is less frequent. * modules/warn-on-use: New file. * build-aux/warn-on-use.h: Likewise. * m4/warn-on-use.m4: Likewise. * MODULES.html.sh (Support for building): Mention it. Signed-off-by: Eric Blake <ebb9@byu.net>

--- a/MODULES.html.sh	Sun Jan 10 23:58:34 2010 +0100
+++ b/MODULES.html.sh	Wed Dec 16 14:53:06 2009 -0700
@@ -3172,6 +3172,7 @@
 
   func_begin_table
   func_module absolute-header
+  func_module arg-nonnull
   func_module config-h
   func_module configmake
   func_module dummy
@@ -3184,14 +3185,15 @@
   func_module lib-msvc-compat
   func_module lib-symbol-versions
   func_module link-warning
+  func_module manywarnings
   func_module no-c++
   func_module relocatable-lib
   func_module relocatable-lib-lgpl
   func_module relocatable-prog
   func_module relocatable-prog-wrapper
   func_module relocatable-script
+  func_module warn-on-use
   func_module warnings
-  func_module manywarnings
   func_end_table
 
   element="Support for building documentation"