[Bug c++/56100] New: spurious -Wshadow warning with local variable in template class

[Bug c++/56100] New: spurious -Wshadow warning with local variable in template class

[f.heckenbach@fh-soft.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56100

             Bug #: 56100
           Summary: spurious -Wshadow warning with local variable in
                    template class
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: f.heckenbach@fh-soft.de


Created attachment 29268
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29268
Test case

Compiling the test case with "-Wshadow" gives:

shadow.cpp: In instantiation of 'void bar<T>::baz() [with T = int]':
shadow.cpp:4:17:   required from 'void bar<T>::qux() [with T = int]'
shadow.cpp:13:21:   required from here
shadow.cpp:6:21: warning: declaration of 'foo' shadows a global declaration
[-Wshadow]
shadow.cpp:9:5: warning: shadowed declaration is here [-Wshadow]

Observed with 4.4.6, 4.6.1 and 4.7.2.

Note: "private" is not necessary to trigger the warning, it's just there to
show it occurs even with "private".

The warning seems strange because the supposedly shadowed variable is declared
after the shadowing one. (I assume that's because of the processing done during
instantiation.) It's annoying because it means that an identifier used in a
template defined in some header, even in a local scope in a private method is
"poisoned" when used anywhere else with -Wshadow.

[Bug c++/56100] spurious -Wshadow warning with local variable in template class

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56100

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-01-24 21:14:51 UTC ---
I think this is an artifact of warning during instantiation rather than at
definition time.

[Bug c++/56100] spurious -Wshadow warning with local variable in template class

[f.heckenbach@fh-soft.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56100

--- Comment #2 from Frank Heckenbach <f.heckenbach@fh-soft.de> 2013-01-24 21:25:09 UTC ---
I guess many warnings can only be given correctly during instantiation because
they depend on the actual arguments.

But shadowing is not one of them as the set of identifiers declared doesn't
depend on the arguments. (Even in the case of partial specializations, one
would expect the warning where the specialization is defined, not when it's
instantiated.)

So perhaps a simple fix is to turn off -Wshadow temporarily during
instantiation. After all, the instantiated code has no access to currently
declared global identifiers. This code fails as it should (AFAIK), unless foo
is declared before the template:

template <typename T>
struct bar
{
  int qux () { return foo; }
};

int foo;

int main ()
{
  bar <int> ().qux ();
}

[Bug c++/56100] spurious -Wshadow warning with local variable in template class

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56100

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-03-31
     Ever confirmed|0                           |1

[Bug c++/56100] spurious -Wshadow warning with local variable in template class

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56100

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Paolo Carlini from comment #3)
> I wonder if in such cases would it simply make sense to suppress the warning
> basing on the locations

I think we want to suppress the warning on instantiation even if the order is
reversed:  given

int foo;

template <typename T>
struct bar
{
  void qux () { baz (); }
private:
  void baz () { int foo; }
};

int main ()
{
  bar <int> ().qux ();
}

We first warn about the declaration in the template, and then again about the
instantiation.

[Bug c++/56100] spurious -Wshadow warning with local variable in template class

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56100

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

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

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Doh, thanks Jason I thought I had already checked the behavior in that case.

[Bug c++/56100] spurious -Wshadow warning with local variable in template class

[paolo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56100

--- Comment #6 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> ---
Author: paolo
Date: Wed Apr  1 21:27:55 2015
New Revision: 221814

URL: https://gcc.gnu.org/viewcvs?rev=221814&root=gcc&view=rev
Log:
/cp
2015-04-01  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/56100
    * pt.c (instantiating_current_function_p): New.
    * name-lookup.c (pushdecl_maybe_friend_1): Use it.
    * cp-tree.h (instantiating_current_function_p): Declare.

/testsuite
2015-04-01  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/56100
    * g++.dg/warn/Wshadow-8.C: New.
    * g++.dg/warn/Wshadow-9.C: Likewise.
    * g++.dg/warn/Wshadow-10.C: Likewise.
    * g++.dg/warn/Wshadow-11.C: Likewise.

Added:
    trunk/gcc/testsuite/g++.dg/warn/Wshadow-10.C
    trunk/gcc/testsuite/g++.dg/warn/Wshadow-11.C
    trunk/gcc/testsuite/g++.dg/warn/Wshadow-8.C
    trunk/gcc/testsuite/g++.dg/warn/Wshadow-9.C
Modified:
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/name-lookup.c
    trunk/gcc/cp/pt.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/56100] spurious -Wshadow warning with local variable in template class

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56100

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
           Assignee|paolo.carlini at oracle dot com    |unassigned at gcc dot gnu.org
   Target Milestone|---                         |5.0

--- Comment #7 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Fixed for 5.0.