[gjs/wip/ptomato/warnings: 10/18] build: Test for %Id as alternate integer output

[Philip Chimento <pchimento src gnome org>]

commit da947c473351fc7db297e0fc8ca19ec32a2d5556
Author: Philip Chimento <philip chimento gmail com>
Date:   Sun Oct 2 12:24:32 2016 -0700

    build: Test for %Id as alternate integer output
    
    %Id is a glibc extension. The "I" character is used elsewhere in other
    extensions too. For example, %I is a Microsoft extension for printing
    size_t. Although undocumented on Darwin, that platform's libc emulates
    the Microsoft extension.
    
    If %I is interpreted as size_t, then the code is likely to crash on
    platforms where int and size_t are different widths, such as 64-bit OSX.
    
    This adds a configure-time check for %Id. When it's not supported, then
    the provided sample program will error out when compiled with -Werror. If
    not supported then we simply print %d since I don't believe the
    alternative representation flag has any other equivalent on other
    platforms.

 configure.ac                |   13 +++++++++++++
 libgjs-private/gjs-util.cpp |    4 ++++
 2 files changed, 17 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 20dd4c1..f9836aa 100644
--- a/configure.ac
+++ b/configure.ac
@@ -27,6 +27,7 @@ AM_SILENT_RULES([yes])
 PKG_PROG_PKG_CONFIG
 PKG_INSTALLDIR
 
+AC_LANG([C++])
 AC_PROG_CXX
 AX_CXX_COMPILE_STDCXX_11
 
@@ -133,6 +134,18 @@ LIBS=$LIBS_no_readline
 
 AC_CHECK_FUNCS([backtrace])
 
+AC_MSG_CHECKING([whether printf() accepts '%Id' for alternative integer output])
+CXXFLAGS_save=$CXXFLAGS
+CXXFLAGS="-Werror -Wformat -pedantic-errors"
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <stdio.h>]],
+  [[printf("%Id", (int)0);]])], [
+    AC_MSG_RESULT([yes])
+    AC_DEFINE([HAVE_PRINTF_ALTERNATIVE_INT], [1],
+      [Define to 1 if printf() accepts '%Id' for alternative integer output])
+  ],
+  [AC_MSG_RESULT([no])])
+CXXFLAGS=$CXXFLAGS_save
+
 AC_ARG_ENABLE(installed_tests,
   [AS_HELP_STRING([--enable-installed-tests],
     [Install test programs @<:@default: no@:>@])])
diff --git a/libgjs-private/gjs-util.cpp b/libgjs-private/gjs-util.cpp
index 961654f..f0e941f 100644
--- a/libgjs-private/gjs-util.cpp
+++ b/libgjs-private/gjs-util.cpp
@@ -31,7 +31,11 @@
 char *
 gjs_format_int_alternative_output(int n)
 {
+#ifdef HAVE_PRINTF_ALTERNATIVE_INT
     return g_strdup_printf("%Id", n);
+#else
+    return g_strdup_printf("%d", n);
+#endif
 }
 
 GType