[Bug c++/55189] New: g++ compiler does not report missing return on function with return type

[Bug c++/55189] New: g++ compiler does not report missing return on function with return type

[meanarbez at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55189

             Bug #: 55189
           Summary: g++ compiler does not report missing return on
                    function with return type
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: meanarbez@gmail.com


Compiled with MinGW port of g++, compiles without errors or warnings:

g++ bug.cpp -o bug.exe

Minimal sample bug.cpp:

        #include <iostream>

        using namespace std;


        class Example
        {
          protected:

            int m_x;

          public:

            Example()
            {
              m_x = 0;
            }

            Example( const Example &ref )
            { 
              m_x = ref.m_x;
            }

            ~Example()
            {
            }

            int get()
            { 
              return m_x;
            }

            void set( int x )
            { 
              m_x = x;
            }

            Example &operator =( Example ref )
            {
              m_x = ref.m_x;
              return *this;
            }
        };


        Example func( Example p )
        {
          Example m;

          m.set( p.get() );

          // ! COMPILER DOES NOT DETECT ABSENCE OF FUNCTION RETURN !
        }


        int main()
        {
          Example m;

          m.set( 7 );

          Example k;

          k = func( m );

          // ! CONSEQUENTLY RESULT IS RANDOM !

          cout << k.get() << endl;

          return 0;
        }

[Bug c++/55189] g++ compiler does not report missing return on function with return type

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55189

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> 2012-11-03 10:40:22 UTC ---
(In reply to comment #0)
> Compiled with MinGW port of g++, compiles without errors or warnings:

It does warn if you ask it to: -Wall

[Bug c++/55189] g++ compiler does not report missing return on function with return type

[meanarbez at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55189

--- Comment #2 from meanone <meanarbez at gmail dot com> 2012-11-03 11:11:15 UTC ---
(In reply to comment #1)
> (In reply to comment #0)
> > Compiled with MinGW port of g++, compiles without errors or warnings:
> 
> It does warn if you ask it to: -Wall

I can understand that this is ok behavior for C, but to have to
EXPLICITLY ASK typesafe language like C++ to inform me if function
WITH RETURN TYPE does not return anything ?

If this is not bug why shouldn't we make

int n;
n =;
printf("%d",n);

to be legal code, compiler should simply assign whatever it wants. Right ?

Could anyone explain what for should missing return on typical C++ function
be useful at all ?

Not to mention probability that it has been forgotten by mistake.

-Wreturn-type should be set by default.

[Bug c++/55189] enable -Wreturn-type by default

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55189

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-11-03
            Summary|g++ compiler does not       |enable -Wreturn-type by
                   |report missing return on    |default
                   |function with return type   |
     Ever Confirmed|0                           |1

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-11-03 13:03:14 UTC ---
(In reply to comment #2)
> If this is not bug why shouldn't we make
> 
> int n;
> n =;
> printf("%d",n);
> 
> to be legal code, compiler should simply assign whatever it wants. Right ?

No, because that's not even legal syntax, so that's a completely different
case.


> -Wreturn-type should be set by default.

OK, so let's change the report to say that then.

In general though, please don't report bugs claiming there are no warnings if
you haven't even tried -Wall, there's a notice when you report a bug asking you
to check that.

Reduced example:

struct A { int i; };

A f()
{
  A a = { 0 };
  // missing return
}

int main()
{
  A a = f();
  return a.i;
}

[Bug c++/55189] enable -Wreturn-type by default

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55189

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-04 14:08:44 UTC ---
Let's do this then.

[Bug c++/55189] enable -Wreturn-type by default

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55189

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
         AssignedTo|paolo.carlini at oracle dot |unassigned at gcc dot
                   |com                         |gnu.org

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-11-04 15:26:09 UTC ---
Sorry, not me, not now: hundreds of testcases need fixing.

[Bug c++/55189] enable -Wreturn-type by default

[sylvestre at debian dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55189

Sylvestre Ledru <sylvestre at debian dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sylvestre at debian dot org

--- Comment #6 from Sylvestre Ledru <sylvestre at debian dot org> ---
Patch proposed here:
http://gcc.gnu.org/ml/gcc-patches/2013-12/msg01781.html

[Bug c++/55189] enable -Wreturn-type by default

[sylvestre at debian dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55189

--- Comment #8 from Sylvestre Ledru <sylvestre at debian dot org> ---
The patches to fix this bug are available here:
https://github.com/sylvestre/gcc
I am doing the legal FSF papers to be able to apply it.

[Bug c++/55189] enable -Wreturn-type by default

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55189

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

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

--- Comment #9 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Sylvestre Ledru from comment #8)
> The patches to fix this bug are available here:
> https://github.com/sylvestre/gcc
> I am doing the legal FSF papers to be able to apply it.

Cool! Hopefully it goes quickly. After that, I would suggest that you submit
the patch to gcc-patches and CC Jason Merrill and Dodji Seketeli, either of
them should be able to approve this.

I noticed that your patch does not update doc/invoke.texi to reflect the fact
that -Wreturn-type is enabled by default instead of by -Wall (it would be great
to automatically generate some parts of the manual from the options
description).

I also noticed that you did not include -Wmissing-return in your patch as
discussed here: http://gcc.gnu.org/ml/gcc/2013-11/msg00288.html

(Perhaps you did, and I am using github incorrectly?)

I think you will get easier approval if you include it (or send two patches in
the same email) and point out to the previous discussion (in particular Dodji,
Joseph and Jason's approval of this idea).
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Subject: [Bug c++/55189] enable -Wreturn-type by default
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55189

--- Comment #10 from Sylvestre Ledru <sylvestre at debian dot org> ---
(In reply to Manuel López-Ibáñez from comment #9)
> 
> Cool! Hopefully it goes quickly. After that, I would suggest that you submit
> the patch to gcc-patches and CC Jason Merrill and Dodji Seketeli, either of
> them should be able to approve this.
Sure. Thanks for the suggestion.

> I noticed that your patch does not update doc/invoke.texi to reflect the
> fact that -Wreturn-type is enabled by default instead of by -Wall (it would
> be great to automatically generate some parts of the manual from the options
> description).
I will have a look!

> I also noticed that you did not include -Wmissing-return in your patch as
> discussed here: http://gcc.gnu.org/ml/gcc/2013-11/msg00288.html
>  
> (Perhaps you did, and I am using github incorrectly?)
I did... removed it :)
I've followed Jason suggestion here:
http://gcc.gnu.org/ml/gcc-patches/2014-01/msg01033.html
The problem that we were trying to address with -Wmissing-return has been fixed
(AFAIK) by the commit description in comment #7

> I think you will get easier approval if you include it (or send two patches
> in the same email) and point out to the previous discussion (in particular
> Dodji, Joseph and Jason's approval of this idea).
Sure. Thanks for the advice.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`866

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r208165 on the trunk (which can of course mean it has been latent
before).