[gnome-common] compiler-flags: Add an optional second argument for custom warnings

[Philip Withnall <pwithnall src gnome org>]

commit c834b24651e1b0f510ede8610bde0be1e940de14
Author: Philip Withnall <philip tecnocode co uk>
Date:   Wed Sep 4 00:48:19 2013 -0600

    compiler-flags: Add an optional second argument for custom warnings
    
    This allows module authors to choose to enforce stricter warnings on
    a per-module basis, to avoid the situation where an outside
    contributor submits a patch which introduces warnings the maintainer
    has enabled locally.
    
    Closes: https://bugzilla.gnome.org/show_bug.cgi?id=707475

 macros2/gnome-compiler-flags.m4 |   14 ++++++++++++--
 1 files changed, 12 insertions(+), 2 deletions(-)
---
diff --git a/macros2/gnome-compiler-flags.m4 b/macros2/gnome-compiler-flags.m4
index 4cb24aa..7504482 100644
--- a/macros2/gnome-compiler-flags.m4
+++ b/macros2/gnome-compiler-flags.m4
@@ -2,6 +2,11 @@ dnl GNOME_COMPILE_WARNINGS
 dnl Turn on many useful compiler warnings and substitute the result into
 dnl WARN_CFLAGS
 dnl For now, only works on GCC
+dnl Pass the default value of the --enable-compile-warnings configure option as
+dnl the first argument to the macro, defaulting to 'yes'.
+dnl Additional warning/error flags can be passed as an optional second argument.
+dnl
+dnl For example: GNOME_COMPILE_WARNINGS([maximum],[-Werror=some-flag -Wfoobar])
 AC_DEFUN([GNOME_COMPILE_WARNINGS],[
     dnl ******************************
     dnl More compiler warnings
@@ -41,6 +46,11 @@ AC_DEFUN([GNOME_COMPILE_WARNINGS],[
         -Werror=missing-include-dirs \
     "
 
+    dnl Additional warning or error flags provided by the module author to
+    dnl allow stricter standards to be imposed on a per-module basis.
+    dnl The author can pass -W or -Werror flags here as they see fit.
+    additional_flags="m4_default([$2],[])"
+
     case "$enable_compile_warnings" in
     no)
         warning_flags=
@@ -49,10 +59,10 @@ AC_DEFUN([GNOME_COMPILE_WARNINGS],[
         warning_flags="-Wall"
         ;;
     yes)
-        warning_flags="$base_warn_flags $base_error_flags"
+        warning_flags="$base_warn_flags $base_error_flags $additional_flags"
         ;;
     maximum|error)
-        warning_flags="$base_warn_flags $base_error_flags"
+        warning_flags="$base_warn_flags $base_error_flags $additional_flags"
         ;;
     *)
         AC_MSG_ERROR(Unknown argument '$enable_compile_warnings' to --enable-compile-warnings)