Re: -Werror considered harmful

[Tristan Van Berkom <tvb gnome org>]

Hi Behdad.

I'll be the first to agree that -Werror is evil stuff, we even fell
into this catch 22 only
around a year ago where one group thought it was a good idea to infect
our builds
with -Werror, while another group thought it was a good idea to add
deprecation warnings,
... I'm not even sure we're out of the woods from that tangled mess yet.
(and I'll side with the latter, deprecation warnings are a good thing,
warnings are a
good thing in general).

That being said, does glib not use the gnome-common macros,
which include the --disable-fatal-warnings configure option ?

I've found this configure option to be helpful, not sure if glib still
needs it to be added...

Cheers,
         -Tristan

On Tue, Feb 26, 2013 at 10:39 AM, Behdad Esfahbod <behdad behdad org> wrote:
> [I think I'm not on d-d-l, CC is appreciated.]
>
> <rant>
>
> Hi,
>
> I'm sending this email instead of filing a bug because I think I need to say
> this as widely as I can: modules adding -Werror (or -Werror=... variants
> thereof) are harmful
>
> Background:
>
> A few years ago Javier opened this bug against gnome-common:
>
>   https://bugzilla.gnome.org/show_bug.cgi?id=608953
>
> which references my blogpost:
>
>   http://mces.blogspot.ca/2008/12/year-end-cleaning-ie-on-warning-options.html
>
> The bug title is "Add some more compiler warning options".  Something that I
> thinks is good hygiene.  However, in the course of that happening, things like
> these ended up going in:
>
>     dnl These compiler flags typically indicate very broken or suspicious
>     dnl code.  Some of them such as implicit-function-declaration are
>     dnl just not default because gcc compiles a lot of legacy code.
>     dnl We choose to make this set into explicit errors.
>     base_error_flags=" \
>         -Werror=missing-prototypes \
>         -Werror=implicit-function-declaration \
>         -Werror=pointer-arith \
>         -Werror=init-self \
>         -Werror=format-security \
>         -Werror=format=2 \
>         -Werror=missing-include-dirs \
>     "
>
> which then made it into glib as part of bug 687385.
>
> Now, can you spot the problem?  Hint: the comment above says "*typically*
> indicate very broken".  I translate: "typically this is fine, in other
> situations we are breaking people's build, but that's fine".
>
> Indeed, the email that went out with the change [1] acknowledged the problem:
>
> "This gets to the next problem, which is that -Wall includes
> -Wmaybe-uninitialized and other heuristics like -Wstrict-aliasing.  Then
> combine that with the fact that some people have got it in their head
> that "-Wall -Werror" is the Right Thing, what actually ends up happening
> is your code only compiles on a *particular version* of gcc.  That just
> doesn't work in a distributed project like GNOME, where various bits get
> reused by different projects and products on different schedules etc."
>
> but goes on to conclude:
>
> "So I think what Dan has is more the Right Thing - make the compiler
> warnings that you should *never* hit into explicit errors."
>
> Interesting.  So some omniscient hacker decided that compilers compiling GNOME
> shall never ever see code that generates a missing-prototypes warning, err,
> error.  Not in the cryptic system headers of whatever weird cross compiler I
> may be using.  I want your crystal ball seized!
>
> Here I am, trying to cross-compile glib using mingw32, so I can cross-compile
> pango, so I can fix a pangowin32 bug, and was stopped getting this:
>
> behdad:libcharset 2$ make V=1
> /bin/sh ../../libtool  --tag=CC   --mode=compile i586-mingw32msvc-gcc
> -DHAVE_CONFIG_H -I. -I../../../glib/libcharset -I../..
> -DLIBDIR=\"/home/behdad/.local/i586-mingw32msvc/lib\" -I../..
> -I/home/behdad/.local/i586-mingw32msvc/include   -g -O2 -mms-bitfields  -Wall
> -Wstrict-prototypes -Werror=declaration-after-statement
> -Werror=missing-prototypes -Werror=implicit-function-declaration
> -Werror=pointer-arith -Werror=init-self -Werror=format=2
> -Werror=missing-include-dirs -MT localcharset.lo -MD -MP -MF
> .deps/localcharset.Tpo -c -o localcharset.lo
> ../../../glib/libcharset/localcharset.c
> libtool: compile:  i586-mingw32msvc-gcc -DHAVE_CONFIG_H -I.
> -I../../../glib/libcharset -I../..
> -DLIBDIR=\"/home/behdad/.local/i586-mingw32msvc/lib\" -I../..
> -I/home/behdad/.local/i586-mingw32msvc/include -g -O2 -mms-bitfields -Wall
> -Wstrict-prototypes -Werror=declaration-after-statement
> -Werror=missing-prototypes -Werror=implicit-function-declaration
> -Werror=pointer-arith -Werror=init-self -Werror=format=2
> -Werror=missing-include-dirs -MT localcharset.lo -MD -MP -MF
> .deps/localcharset.Tpo -c ../../../glib/libcharset/localcharset.c
> -DDLL_EXPORT -DPIC -o .libs/localcharset.o
> In file included from ../../../glib/libcharset/localcharset.c:28:
> /usr/lib/gcc/i586-mingw32msvc/4.2.1-sjlj/../../../../i586-mingw32msvc/include/stdio.h:372:
> error: no previous prototype for 'getc'
> /usr/lib/gcc/i586-mingw32msvc/4.2.1-sjlj/../../../../i586-mingw32msvc/include/stdio.h:379:
> error: no previous prototype for 'putc'
> /usr/lib/gcc/i586-mingw32msvc/4.2.1-sjlj/../../../../i586-mingw32msvc/include/stdio.h:386:
> error: no previous prototype for 'getchar'
> /usr/lib/gcc/i586-mingw32msvc/4.2.1-sjlj/../../../../i586-mingw32msvc/include/stdio.h:393:
> error: no previous prototype for 'putchar'
> In file included from ../../../glib/libcharset/localcharset.c:28:
> /usr/lib/gcc/i586-mingw32msvc/4.2.1-sjlj/../../../../i586-mingw32msvc/include/stdio.h:535:
> error: no previous prototype for 'fopen64'
> /usr/lib/gcc/i586-mingw32msvc/4.2.1-sjlj/../../../../i586-mingw32msvc/include/stdio.h:547:
> error: no previous prototype for 'ftello64'
> /usr/lib/gcc/i586-mingw32msvc/4.2.1-sjlj/../../../../i586-mingw32msvc/include/stdio.h:606:
> error: no previous prototype for 'vsnwprintf'
>
>
> Please, please, please, really, stop acting as if you know my build
> environment...  If I want errors, I'll enable them myself.
>
> </rant>
>
> [1] https://mail.gnome.org/archives/desktop-devel-list/2012-July/msg00100.html
>
> --
> behdad
> http://behdad.org/
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