[Bug c++/64431] New: "-Wignored-qualifiers" warning gives misleading position in code

[Bug c++/64431] New: "-Wignored-qualifiers" warning gives misleading position in code

[rutsky.vladimir at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64431

            Bug ID: 64431
           Summary: "-Wignored-qualifiers" warning gives misleading
                    position in code
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rutsky.vladimir at gmail dot com

"type qualifiers ignored on function return type" warning doesn't point in
"const" that is being ignored, but instead it points to function arguments or
function qualifiers.

Consider following example:

$ cat ignored_qualifiers.cpp
struct C
{
    const int f1();
    const int f2(float);
    const int f3(char *, int);
    const int f4() volatile const;
    const int f5() const volatile;
};

const int f6();
const int f7(float);
const int f8(char *, int);


$ g++-4.9 -c -Wignored-qualifiers ignored_qualifiers.cpp
ignored_qualifiers.cpp:3:18: warning: type qualifiers ignored on function
return type [-Wignored-qualifiers]
     const int f1();
                  ^
ignored_qualifiers.cpp:4:23: warning: type qualifiers ignored on function
return type [-Wignored-qualifiers]
     const int f2(float);
                       ^
ignored_qualifiers.cpp:5:29: warning: type qualifiers ignored on function
return type [-Wignored-qualifiers]
     const int f3(char *, int);
                             ^
ignored_qualifiers.cpp:6:29: warning: type qualifiers ignored on function
return type [-Wignored-qualifiers]
     const int f4() volatile const;
                             ^
ignored_qualifiers.cpp:7:26: warning: type qualifiers ignored on function
return type [-Wignored-qualifiers]
     const int f5() const volatile;
                          ^
ignored_qualifiers.cpp:10:14: warning: type qualifiers ignored on function
return type [-Wignored-qualifiers]
 const int f6();
              ^
ignored_qualifiers.cpp:11:19: warning: type qualifiers ignored on function
return type [-Wignored-qualifiers]
 const int f7(float);
                   ^
ignored_qualifiers.cpp:12:25: warning: type qualifiers ignored on function
return type [-Wignored-qualifiers]
 const int f8(char *, int);
                         ^


Expected behavior: the warning should point on "const" in the return value of a
funtion.
For example:


ignored_qualifiers.cpp:7:26: warning: type qualifiers ignored on function
return type [-Wignored-qualifiers]
     const int f5() const volatile;
     ^



$ g++-4.9 --version
g++-4.9 (Ubuntu 4.9.2-0ubuntu1~14.04) 4.9.2
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[Bug c++/64431] "-Wignored-qualifiers" warning gives misleading position in code

[rutsky.vladimir at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64431

--- Comment #1 from Vladimir Rutsky <rutsky.vladimir at gmail dot com> ---
$ g++-4.9 -v
Using built-in specs.
COLLECT_GCC=g++-4.9
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.9/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
4.9.2-0ubuntu1~14.04' --with-bugurl=file:///usr/share/doc/gcc-4.9/README.Bugs
--enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.9 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.9 --libdir=/usr/lib --enable-nls
--with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-vtable-verify
--enable-plugin --with-system-zlib --disable-browser-plugin
--enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.9-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.9.2 (Ubuntu 4.9.2-0ubuntu1~14.04)

[Bug c++/64431] "-Wignored-qualifiers" warning gives misleading position in code

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64431

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-12-29
                 CC|                            |manu at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #2 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
This is a problem also in C, however, in C++ it is trivial to fix:

Index: gcc/cp/decl.c
===================================================================
--- gcc/cp/decl.c       (revision 218749)
+++ gcc/cp/decl.c       (working copy)
@@ -9686,11 +9686,11 @@ grokdeclarator (const cp_declarator *dec
               Make sure we have a valid type for the function to return.  */

            if (type_quals != TYPE_UNQUALIFIED)
              {
                if (SCALAR_TYPE_P (type) || VOID_TYPE_P (type))
-                 warning (OPT_Wignored_qualifiers,
+                 warning_at (declspecs->locations[ds_const],
OPT_Wignored_qualifiers,
                           "type qualifiers ignored on function return type");
                /* We now know that the TYPE_QUALS don't apply to the
                   decl, but to its return type.  */
                type_quals = TYPE_UNQUALIFIED;
              }

I would suggest to add a testcase with explicit column numbers.

I added this to the list of EasyHacks and I'll leave it to a new dev to fix it
(see
https://gcc.gnu.org/wiki/GettingStarted#Basics:_Contributing_to_GCC_in_10_easy_steps
if you want to be the one)
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd377

Sandra Loosemore <sandra at codesourcery dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at ucw dot cz
           Assignee|sandra at codesourcery dot com     |unassigned at gcc dot gnu.org

--- Comment #3 from Sandra Loosemore <sandra at codesourcery dot com> ---
This has been discussed on the gcc-patches mailing list in this thread:

https://gcc.gnu.org/ml/gcc-patches/2014-11/msg02616.html

[Bug c++/64431] "-Wignored-qualifiers" warning gives misleading position in code

[eugene.zelenko at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64431

Eugene Zelenko <eugene.zelenko at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |eugene.zelenko at gmail dot com

--- Comment #3 from Eugene Zelenko <eugene.zelenko at gmail dot com> ---
Same problem exists in 4.8.2 and 4.8.3 and probably earlier versions.

Will be good idea to fix problem there too.

Eugene.

[Bug c++/64431] "-Wignored-qualifiers" warning gives misleading position in code

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64431

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|rutsky.vladimir at gmail dot com   |
           Assignee|unassigned at gcc dot gnu.org      |paolo.carlini at oracle dot com

--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Mine.

[Bug c++/64431] "-Wignored-qualifiers" warning gives misleading position in code

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64431

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Note that, besides the cases of volatile and restrict which should be also
included, already have a patch including those, we need further tweaks to
recover the location of 'const' in:

   int* const f9();