Created attachment 14892 [details]
gcc-cpp-Werror-message.patch

Proposed patch.

I agree this is a bug.

I think this patch is insufficient.  For best results I think that
libcpp and diagnostic.c should agree on whether the "warnins being treated
as errors" message has been emitted.

One way to do this would be to finally switch libcpp to emit all errors
via diagnostic.c.  Though I suppose that, even if we do this, we may still
need something like this patch for other users of libcpp.

Created attachment 14977 [details]
gcc-cpp-Werror-message-cpp-diagnostic.patch

Is this what you meant?  Not sure whether I've got the source_location stuff correct, but it seems to work.

Created attachment 14980 [details]
gcc-cpp-Werror-message.patch

Also when preprocessing-only.

Created attachment 14981 [details]
gcc-cpp-Werror-message.patch

Created attachment 14993 [details]
gcc-cpp-Werror-message.patch

Try to handle system-header and inhibit conditions/flags correctly.

Created attachment 14994 [details]
gcc-cpp-Werror-message.patch

de-obfuscate the pedwarn code path

(In reply to comment #7)
> Created an attachment (id=14994) [edit]
> gcc-cpp-Werror-message.patch
> 
> de-obfuscate the pedwarn code path
> 

Hi, Ed, not sure whether you know that for us to be able to accept your patch, you need a copyright assignment form with the FSF: http://gcc.gnu.org/contribute.html#legal

This is fixed by my patch to make cpplib always use the diagnostic.c
infrastructure: http://gcc.gnu.org/ml/gcc-patches/2009-02/msg00491.html

(This change is the cause of the Wvariadic-1.c and Wvariadic-3.c testcase
changes in that patch.)

Thus, assigning the bug to myself.

Subject: Bug 34695

Author: jsm28
Date: Sun Mar 29 22:56:07 2009
New Revision: 145263

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=145263
Log:
	PR preprocessor/34695

gcc:
	* Makefile.in (c-opts.o): Depend on c-tree.h.
	* c-common.c: Move down include of diagnostic.h.
	(done_lexing, c_cpp_error): New.
	* c-common.h (done_lexing): Declare.
	* c-decl.c (c_write_global_declarations): Don't check cpp_errors
	(parse_in).
	* c-opts.c: Include c-tree.h.
	(c_common_init_options): Set preprocessor error callback.
	(c_common_handle_option): Do not set preprocessor
	inhibit_warnings, warnings_are_errors, warn_system_headers,
	pedantic_errors or inhibit_warnings flags.
	(c_common_post_options): Do not check cpp_errors (parse_in).
	(c_common_finish): Do not output dependencies if there were
	errors.  Do not check return value of cpp_finish.
	* c-ppoutput.c (pp_file_change): Set input_location.
	* c-tree.h (c_cpp_error): Declare.
	* diagnostic.c (diagnostic_set_info_translated): Also initialize
	override_column.
	(diagnostic_build_prefix): Check override_column.
	* diagnostic.h (diagnostic_info): Add override_column field.
	(diagnostic_override_column): Define.

gcc/cp:
	* cp-tree.h (cp_cpp_error): Remove.
	* error.c (cp_cpp_error): Remove.
	* parser.c (cp_lexer_new_main): Set done_lexing instead of
	client_diagnostic and error callback.

gcc/fortran:
	* cpp.c (cb_cpp_error): New.
	(gfc_cpp_post_options): Don't set cpp_option->inhibit_warnings.
	Don't check cpp_errors (cpp_in).
	(gfc_cpp_init_0): Set cb->error.

gcc/testsuite:
	* gcc.dg/builtin-redefine.c, gcc.dg/cpp/redef2.c,
	gcc.dg/cpp/redef3.c, gcc.dg/cpp/trad/redef2.c: Use dg-message
	instead of dg-warning for "previous definition" messages.
	* gcc.dg/cpp/Wvariadic-1.c, gcc.dg/cpp/Wvariadic-3.c: Expect
	"warnings being treated as errors" message.
	* gcc.dg/fltconst-1.c: Use -fshow-column.

libcpp:
	* makedepend.c: Remove.
	* Makefile.in (makedepend_OBJS, makedepend$(EXEEXT)): Remove.
	(all, clean, TAGS_SOURCES, include): Remove makedepend handling.
	* directives.c (cpp_errors): Remove.
	* errors.c (print_location, _cpp_begin_message, v_message):
	Remove.
	(cpp_error, cpp_error_with_line): Always use error callback.
	(cpp_error, cpp_error_with_line, cpp_errno): Return bool.
	* include/cpplib.h (cpp_options): Remove pedantic_errors,
	inhibit_warnings, warn_system_headers, inhibit_errors,
	warnings_are_errors, client_diagnostic.
	(cpp_callbacks): Add extra arguments to error callback; make it
	return bool.
	(cpp_finish): Return void.
	(cpp_destroy): Remove inaccurate comment about return value.
	(cpp_errors, CPP_DL_EXTRACT, CPP_DL_WARNING_P): Remove.
	(CPP_DL_NOTE): Define.
	* include/line-map.h (linemap_print_containing_files): Remove.
	* init.c (cpp_finish): Do not check for or return number of
	errors.
	* internal.h (cpp_reader): Remove errors field.
	* line-map.c (linemap_print_containing_files): Remove.
	* macro.c (_cpp_create_definition): Use CPP_DL_NOTE for message
	about previous definition.  Only emit it if previous diagnostic
	was emitted.

Removed:
    trunk/libcpp/makedepend.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/Makefile.in
    trunk/gcc/c-common.c
    trunk/gcc/c-common.h
    trunk/gcc/c-decl.c
    trunk/gcc/c-opts.c
    trunk/gcc/c-ppoutput.c
    trunk/gcc/c-tree.h
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/error.c
    trunk/gcc/cp/parser.c
    trunk/gcc/diagnostic.c
    trunk/gcc/diagnostic.h
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/cpp.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/builtin-redefine.c
    trunk/gcc/testsuite/gcc.dg/cpp/Wvariadic-1.c
    trunk/gcc/testsuite/gcc.dg/cpp/Wvariadic-3.c
    trunk/gcc/testsuite/gcc.dg/cpp/redef2.c
    trunk/gcc/testsuite/gcc.dg/cpp/redef3.c
    trunk/gcc/testsuite/gcc.dg/cpp/trad/redef2.c
    trunk/gcc/testsuite/gcc.dg/fltconst-1.c
    trunk/libcpp/ChangeLog
    trunk/libcpp/Makefile.in
    trunk/libcpp/directives.c
    trunk/libcpp/errors.c
    trunk/libcpp/include/cpplib.h
    trunk/libcpp/include/line-map.h
    trunk/libcpp/init.c
    trunk/libcpp/internal.h
    trunk/libcpp/line-map.c
    trunk/libcpp/macro.c

Fixed for 4.5.