Some warning options are, for reasons not entirely obvious to me, not

supported by some versions of g++ even though the corresponding version
of gcc supports them.  Other versions of g++, and clang, support them.

Check, before adding a -W option for C++, whether the compiler supports
it; that check must be done with -Werror, at least with g++, in order to
get a non-zero exit status from the compiler.

svn path=/trunk/; revision=54447

2 files changed, 50 insertions, 3 deletions

diff --git a/acinclude.m4 b/acinclude.m4
index bf55755921..61348f1489 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -1610,6 +1610,37 @@ AC_DEFUN([AC_WIRESHARK_CHECK_UNKNOWN_WARNING_OPTION_ERROR],
 	CFLAGS="$save_CFLAGS"
     ])
 
+dnl
+dnl Check whether, if you pass a valid-for-C-but-not-C++ option to the
+dnl compiler, it fails or just prints a warning message and succeeds.
+dnl Set ac_wireshark_non_cxx_warning_option_error to the appropriate flag
+dnl to force an error if it would otherwise just print a warning message
+dnl and succeed.
+dnl
+AC_DEFUN([AC_WIRESHARK_CHECK_NON_CXX_WARNING_OPTION_ERROR],
+    [
+	AC_MSG_CHECKING([whether the compiler fails when given an warning option not supported for C++])
+	save_CXXFLAGS="$CXXFLAGS"
+	CXXFLAGS="$CFLAGS -Wmissing-prototypes" # the prototypical one, no pun intended
+	AC_LANG_PUSH(C++)
+	AC_TRY_COMPILE(
+	    [],
+	    [return 0],
+	    [
+		AC_MSG_RESULT([no, adding -Werror])
+		#
+		# We're assuming this is g++, where -Werror is the
+		# appropriate option to force the compiler to fail.
+		# 
+		ac_wireshark_non_cxx_warning_option_error="-Werror"
+	    ],
+	    [
+		AC_MSG_RESULT([yes])
+	    ])
+	AC_LANG_POP
+	CXXFLAGS="$save_CXXFLAGS"
+    ])
+
 #
 # AC_WIRESHARK_COMPILER_FLAGS_CHECK
 #
@@ -1720,11 +1751,21 @@ if test "x$ac_supports_gcc_flags" = "xyes" ; then
     #
     # Not C-only; if this can be added to the C++ compiler flags, add them.
     #
+    # If the option begins with "-W", add
+    # $ac_wireshark_unknown_warning_option_error, as per the above, and
+    # also add $ac_wireshark_non_cxx_warning_option_error, because at
+    # lease some versions of g++ whine about -Wmissing-prototypes, the
+    # fact that at least one of those versions refuses to warn about
+    # function declarations without an earlier declaration nonwithstanding;
+    # perhaps there's a reason not to warn about that with C++ even though
+    # warning about it can be a Good Idea with C, but it's not obvious to
+    # me).
+    #
     AC_MSG_CHECKING(whether we can add $GCC_OPTION to CXXFLAGS)
     CXXFLAGS_saved="$CXXFLAGS"
     if expr "x$GCC_OPTION" : "x-W.*" >/dev/null
     then
-      CXXFLAGS="$CXXFLAGS $ac_wireshark_unknown_warning_option_error $GCC_OPTION"
+      CXXFLAGS="$CXXFLAGS $ac_wireshark_unknown_warning_option_error $ac_wireshark_non_cxx_warning_option_error $GCC_OPTION"
     elif expr "x$GCC_OPTION" : "x-f.*" >/dev/null
     then
       CXXFLAGS="$CXXFLAGS -Werror $GCC_OPTION"
diff --git a/configure.ac b/configure.ac
index 8fec259059..2505ac1a27 100644
--- a/configure.ac
+++ b/configure.ac
@@ -750,12 +750,18 @@ fi
 AC_SUBST(HAVE_OSX_PACKAGING)
 
 #
-# Some compilers have to be told to fail on unknown warning errors;
+# Some compilers have to be told to fail when passed an unknown -W flag;
 # make sure we do that.
 #
 AC_WIRESHARK_CHECK_UNKNOWN_WARNING_OPTION_ERROR
 
 #
+# Some C++ compilers have to be told to fail when passed a -W flag that
+# they don't think should apply to C++; make sure we do that.
+#
+AC_WIRESHARK_CHECK_NON_CXX_WARNING_OPTION_ERROR
+
+#
 # Try to add some additional gcc checks to CFLAGS
 #
 AC_ARG_ENABLE(extra-gcc-checks,
@@ -801,7 +807,7 @@ AC_ARG_ENABLE(extra-gcc-checks,
 		#
 		# All the registration functions block these for now.
 		#
-		AC_WIRESHARK_COMPILER_FLAGS_CHECK(-Wmissing-prototypes, C)
+		AC_WIRESHARK_COMPILER_FLAGS_CHECK(-Wmissing-prototypes)
 		AC_WIRESHARK_COMPILER_FLAGS_CHECK(-Wmissing-declarations)
 		#
 		# A bunch of "that might not work on SPARC" code blocks