[Bug c++/51851] New: Overriding a function with a parameter of dependent type fails to override.

[Bug c++/51851] New: Overriding a function with a parameter of dependent type fails to override.

[ville.voutilainen at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51851

             Bug #: 51851
           Summary: Overriding a function with a parameter of dependent
                    type fails to override.
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ville.voutilainen@gmail.com


Test snippet:

template<class T>
struct A
{
       typedef double Point[2];
       virtual double calculate(const Point point) const = 0;
};

template<class T>
struct B : public A<T>
{
       virtual double calculate(const typename A<T>::Point point) const
       {
               return point[0];
       }
};

int main()
{
       B<int> b;
       return 0;
}

gcc says
ville.cpp: In function ‘int main()’:
ville.cpp:19:16: error: cannot declare variable ‘b’ to be of abstract type
‘B<int>’
ville.cpp:9:8: note:   because the following virtual functions are pure within
‘B<int>’:
ville.cpp:5:24: note:     double A<T>::calculate(const double*) const [with T =
int]

[Bug c++/51851] Overriding a function with a parameter of dependent type fails to override.

[ville.voutilainen at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51851

--- Comment #1 from Ville Voutilainen <ville.voutilainen at gmail dot com> 2012-01-13 19:13:13 UTC ---
Johannes Schaub says "in both situations the question is whether the parameter
type adjustments happen immediately or after instantiation (when T is replaced
by the actual type)", regarding the possibility that
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49051
is related.

[Bug c++/51851] Overriding a function with a parameter of dependent type fails to override.

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51851

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |SUSPENDED
   Last reconfirmed|                            |2012-01-13
                 CC|                            |jason at gcc dot gnu.org
     Ever Confirmed|0                           |1

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> 2012-01-13 20:49:44 UTC ---
This is core issue 1001; see my reply in CWG.

[Bug c++/51851] [core/1001] Overriding a function with a parameter of dependent type fails to override.

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51851

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nickhuang99 at hotmail dot com

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
*** Bug 101402 has been marked as a duplicate of this bug. ***

[Bug c++/51851] [core/1001] Overriding a function with a parameter of dependent type fails to override.

[nickhuang99 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51851

--- Comment #4 from qingzhe huang <nickhuang99 at hotmail dot com> ---
At least since release/gcc-10, this test code has been successfully compiled.
Can we change its status to Resolved?

[Bug c++/51851] [core/1001] Overriding a function with a parameter of dependent type fails to override.

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51851

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The example in CWG 1001 still doesn't compile (as you noted in PR 101402) and
CWG 1001 is still open. So no, this shouldn't be closed as resolved yet.

[Bug c++/51851] [core/1001] Overriding a function with a parameter of dependent type fails to override.

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51851

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The case here is accepted since r10-7622:

c++: Function type and parameter type disagreements [PR92010]

This resolves parts of Core issues 1001/1322 by rebuilding the function type
of an instantiated function template in terms of its formal parameter types
whenever the original function type and formal parameter types disagree about
the type of a parameter after substitution.

[Bug c++/51851] [core/1001] Overriding a function with a parameter of dependent type fails to override.

[nickhuang99 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51851

--- Comment #7 from qingzhe huang <nickhuang99 at hotmail dot com> ---
Thank you for clarifications!

I just found a solution for this 10-year-old issue and preparing a patch.
However, the solution is not able to solve more complicated cases which
requires more work.
This issue is so complicated and I am hesitating to file more complicated bugs
which this patch won't work because it requires improvement work of function
*resolve_typename_type* to handle recursive case correctly.



diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 3414cbdc876..db0d43b2b08 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -14493,7 +14493,16 @@ grokparms (tree parmlist, tree *parms)

          /* Top-level qualifiers on the parameters are
             ignored for function types.  */
-         type = cp_build_qualified_type (type, 0);
+         int type_quals = 0;
+         /* Top-level qualifiers are reserved for array type. PR101783 */
+         if (TREE_CODE (type) == TYPENAME_TYPE)
+         {
+            tree resolved_type = resolve_typename_type(type, false);
+            if (resolved_type && TREE_CODE(resolved_type) == ARRAY_TYPE)
+               type_quals = CP_TYPE_CONST_P(type);
+         }
+         type = cp_build_qualified_type (type, type_quals);
+
          if (TREE_CODE (type) == METHOD_TYPE)
            {
              error ("parameter %qD invalidly declared method type", decl);

[Bug c++/51851] [core/1001] Overriding a function with a parameter of dependent type fails to override.

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51851

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:79802c5dcc043a515f429bb2bec7573b8537c32a

commit r12-4453-g79802c5dcc043a515f429bb2bec7573b8537c32a
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Sep 28 10:02:04 2021 -0400

    c++: array cv-quals and template specialization [PR101402]

    PRs 101402, 102033, etc. demonstrated that the fix for PR92010 wasn't
    handling all cases of the CWG1001/1322 issue with parameter type qual
    stripping and arrays with templates.  The problem turned out to be in
    determine_specialization, which did an extra substitution without the 92010
    fix and then complained that the result didn't match.

    But just removing that wrong/redundant code meant that we were accepting
    specializations with different numbers of parameters, because the code in
    fn_type_unification that compares types in this case wasn't checking for
    length mismatch.

    After fixing that, I realized that fn_type_unification couldn't tell the
    difference between variadic and non-variadic function types, because the
    args array doesn't include the terminal void we use to indicate
non-variadic
    function type.  So I added it, and made the necessary adjustments.

    Thanks to qingzhe "nick" huang <nickhuang99@hotmail.com> for the patch that
    led me to dig more into this, and the extensive testcases.

            PR c++/51851
            PR c++/101402
            PR c++/102033
            PR c++/102034
            PR c++/102039
            PR c++/102044

    gcc/cp/ChangeLog:

            * pt.c (determine_specialization): Remove redundant code.
            (fn_type_unification): Check for mismatched length.
            (type_unification_real): Ignore terminal void.
            (get_bindings): Don't stop at void_list_node.
            * class.c (resolve_address_of_overloaded_function): Likewise.

    gcc/testsuite/ChangeLog:

            * g++.dg/template/fnspec2.C: New test.
            * g++.dg/template/parm-cv1.C: New test.
            * g++.dg/template/parm-cv2.C: New test.
            * g++.dg/template/parm-cv3.C: New test.