[Bug c++/50134] New: -Wmissing-prototypes doesn't work for C++

[Bug c++/50134] New: -Wmissing-prototypes doesn't work for C++

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

             Bug #: 50134
           Summary: -Wmissing-prototypes doesn't work for C++
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hjl.tools@gmail.com


[hjl@gnu-33 gcc]$ cat x.c
int
foo (int x)
{
 return x;
}
[hjl@gnu-33 gcc]$ ./xgcc -B./ -S -O -Wmissing-prototypes x.c
x.c:2:1: warning: no previous prototype for ‘foo’ [-Wmissing-prototypes]
[hjl@gnu-33 gcc]$ ./g++ -B./ -S -O -Wmissing-prototypes x.c
cc1plus: warning: command line option ‘-Wmissing-prototypes’ is valid
for Ada/AdaWhy/C/ObjC but not for C++ [enabled by default]
[hjl@gnu-33 gcc]$ ./g++ -B./ -S -O x.c
[hjl@gnu-33 gcc]$ ./g++ -B./ -Wall -S -O x.c
[hjl@gnu-33 gcc]$

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[schwab@linux-m68k.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> 2011-08-20 08:37:21 UTC ---
-Wmissing-declaration should do what you want.

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-30 00:45:22 UTC ---
So closing.

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu.org

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2011-09-30 06:54:59 UTC ---
What is the difference between Wmissing-prototypes and Wmissing-declarations?

 -Wmissing-prototypes (C and Objective-C only)
           Warn if a global function is defined without a previous prototype
declaration.  This warning is issued even if the definition itself provides a
prototype.  The aim is to detect global functions that fail to be declared in
header files.

       -Wmissing-declarations
           Warn if a global function is defined without a previous declaration.
 Do so even if the definition itself provides a prototype.  Use this option to
detect global functions that are not declared in header files.  In C++, no
warnings are issued
           for function templates, or for inline functions, or for functions in
anonymous namespaces.


They seem exactly the same thing!

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #4 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2011-09-30 07:00:40 UTC ---
So Joseph, Jason, what is the difference between Wmissing-prototypes and
Wmissing-declarations?

Can't you just make one a synonym for the other and make one of them the
canonical form?

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-09-30 08:04:38 UTC ---
C++ doesn't have prototypes, it has declarations and definitions, so the
different names makes sense.

I'm not sure what "Do so even if the definition itself provides a prototype."
means in the context of C++.

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #6 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2011-09-30 14:16:40 UTC ---
On Fri, 30 Sep 2011, redi at gcc dot gnu.org wrote:

> I'm not sure what "Do so even if the definition itself provides a prototype."
> means in the context of C++.

That's simple enough: it's a style warning: a global function should be 
declared in a header, so warn for

int
f (void)
{
  return 0; 
}

if there was no previous declaration for f.  (For C++, the definition and 
any previous declaration will always provide a prototype.)

As Ian said in <http://gcc.gnu.org/ml/gcc/2011-08/msg00366.html>, for C++ 
the two options reduce to the same thing because no non-prototype 
declarations or definitions exist.  For C,

int f();
int f(void) { return 0; }

gets a warning with -Wmissing-prototypes but not -Wmissing-declarations, 
because "int f();" is a non-prototype declaration in C.

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-09-30 14:29:18 UTC ---
(In reply to comment #6)
> On Fri, 30 Sep 2011, redi at gcc dot gnu.org wrote:
> 
> > I'm not sure what "Do so even if the definition itself provides a prototype."
> > means in the context of C++.
> 
> That's simple enough: it's a style warning: a global function should be 
> declared in a header, so warn for
> 
> int
> f (void)
> {
>   return 0; 
> }
> 
> if there was no previous declaration for f.

I get that part.

>  (For C++, the definition and 
> any previous declaration will always provide a prototype.)

Exactly, that's my point.  But I had missed the fact that the option is valid
in C as well as C++.

My uncertainty was about what that sentence means in the context of C++, and
the answer is nothing, because there are no definitions which do not provide a
prototype in C++ (ignoring the fact that "prototype" doesn't mean anything in
C++).

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |ASSIGNED
   Last reconfirmed|                            |2012-05-15
         Resolution|INVALID                     |
     Ever Confirmed|0                           |1

--- Comment #8 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-05-15 12:03:57 UTC ---
I will update invoke.texi to make this clear. I see a lot of confusion among
users:
http://stackoverflow.com/questions/2389169/how-do-i-get-missing-prototype-warnings-from-g
and GCC developers.

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #9 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-05-15 12:21:36 UTC ---
(In reply to comment #6)
> 
> int f();
> int f(void) { return 0; }
> 
> gets a warning with -Wmissing-prototypes but not -Wmissing-declarations, 
> because "int f();" is a non-prototype declaration in C.

Honestly, I don't see the purpose of this distinction in modern C. I would
rather have -Wmissing-declarations be an alias of -Wmissing-prototypes in C,
and simplify both GCC and the life of users.

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #10 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-05-15 12:23:50 UTC ---
Nonetheless, this is a patch that explains the current situation:

--- gcc/doc/invoke.texi (revision 187462)
+++ gcc/doc/invoke.texi (working copy)
@@ -4413,21 +4413,26 @@ This warning is also enabled by @option{
 @item -Wmissing-prototypes @r{(C and Objective-C only)}
 @opindex Wmissing-prototypes
 @opindex Wno-missing-prototypes
 Warn if a global function is defined without a previous prototype
 declaration.  This warning is issued even if the definition itself
-provides a prototype.  The aim is to detect global functions that 
-are not declared in header files.
+provides a prototype. The aim is to detect global functions that are
+not declared in header files, independently of whether the declaration
+is a prototype.  This option does not apply to C++ because there is no
+concept of prototype.  Use @option{-Wmissing-declarations} to detect
+missing declarations in C++.

 @item -Wmissing-declarations
 @opindex Wmissing-declarations
 @opindex Wno-missing-declarations
 Warn if a global function is defined without a previous declaration.
-Do so even if the definition itself provides a prototype.
-Use this option to detect global functions that are not declared in
-header files.  In C++, no warnings are issued for function templates,
-or for inline functions, or for functions in anonymous namespaces.
+Do so even if the definition itself provides a prototype.  Use this
+option to detect global functions that are not declared in header
+files.  In C, this option does not warn if there is a previous
+non-prototype declaration; use @option{-Wmissing-prototype} to detect
+those.  In C++, no warnings are issued for function templates, or for
+inline functions, or for functions in anonymous namespaces.

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #11 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-05-24 15:29:42 UTC ---
Manuel, what happened to this, out of curiosity? I see an Assigned status (but
the Assigned To field still blank) and a documentation patchlet of yours in the
audit trail?!

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch
             Status|ASSIGNED                    |NEW

--- Comment #12 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-05-24 18:53:07 UTC ---
I was planning to submit this doc patch for approval, but I am quite busy with
personal stuff right now. Feel free to adopt the patch, if you think it is
interesting enough.

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |redi at gcc dot gnu.org

--- Comment #13 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-05-28 21:42:02 UTC ---
Jon, I'd like to resolve this PR: personally I totally agree with Manuel that
adding a few words of clarification in the docs, in particular explaining that
"prototype" is a C concept, is a good idea, but I'm not 100% sure about the
English. Could you double check the tentative patch here in the audit trail and
possibly post it to the mailing list?

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |redi at gcc dot gnu.org
                   |gnu.org                     |

--- Comment #14 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-05-28 21:47:53 UTC ---
Sure

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #15 from Steven Bosscher <steven at gcc dot gnu.org> 2012-05-30 18:52:18 UTC ---
This bug results in real warnings being introduced unnoticed, see:
http://gcc.gnu.org/ml/gcc-patches/2012-05/msg02005.html

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #16 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2012-05-30 18:58:29 UTC ---
(In reply to comment #15)
> This bug results in real warnings being introduced unnoticed, see:
> http://gcc.gnu.org/ml/gcc-patches/2012-05/msg02005.html

I think somebody tried to add -Wmissing-declarations to CXXFLAGS recently, but
the patch was rejected. Check the archive of gcc-patches for the details. I
think that patch should be accepted for consistency with CFLAGS.

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #17 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-06-01 00:38:41 UTC ---
Updated patch at http://gcc.gnu.org/ml/gcc-patches/2012-06/msg00001.html

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

--- Comment #18 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-06-01 08:47:11 UTC ---
Author: redi
Date: Fri Jun  1 08:47:06 2012
New Revision: 188103

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=188103
Log:
2012-06-01  Manuel López-Ibáñez  <manu@gcc.gnu.org>
            Jonathan Wakely  <jwakely.gcc@gmail.com>

    PR c++/50134
    * doc/invoke.texi (Warning Options): Explain purpose and differences
    between -Wmissing-prototypes and -Wmissing-declarations.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/doc/invoke.texi

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.8.0

--- Comment #19 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-06-01 09:40:11 UTC ---
Manu, Paolo, the doc patch is in, are you happy to close this now?

[Bug c++/50134] -Wmissing-prototypes doesn't work for C++

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50134

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #20 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-06-01 12:39:07 UTC ---
Great, thanks Jon.