[Bug c++/53585] New: template value parameter of pointer-to-member type incorrectly rejects non-direct values

[yacwroy at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53585

             Bug #: 53585
           Summary: template value parameter of pointer-to-member type
                    incorrectly rejects non-direct values
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: yacw...@gmail.com


Created attachment 27561
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27561
c++ testcase - should be legal

Problem:
Pointer-to-member value parameters appear to only accept direct values (of the
immediate form &X::Y) and reject passed constexpr variables.

llvm/clang++ accepts these.

I'm assuming this is legal but I haven't checked the standard.

specs: linux/x64

source (same as attached)
=========================
struct SFoo
    {
        int x;
    };

constexpr int SFoo::* G_ptr_to_x = &SFoo::x;

// Dummy test struct.
template <int SFoo::* P>
struct SBar {};

SBar<G_ptr_to_x> G_bar; // <ERROR>. (This should be legal, and is in clang).

// Additional testing:
SBar<&SFoo::x> G_bar2; // Shows the member-pointer works if immediate.
constexpr int SFoo::* another_ptr = G_ptr_to_x; // Shows "could not convert
..." error message is incorrect.

int main()
    {}
=========================
Errors (build command = g++ mptr.cpp -std=c++11).
=========================
test/misc/mptr.cpp:12:16: error: ‘G_ptr_to_x’ is not a valid template argument
for type ‘int SFoo::*’
 SBar<G_ptr_to_x> G_bar; // <ERROR>. (This should be legal, and is in clang).
                ^
test/misc/mptr.cpp:12:16: error: it must be a pointer-to-member of the form
‘&X::Y’
test/misc/mptr.cpp:12:16: error: could not convert template argument
‘G_ptr_to_x’ to ‘int SFoo::*’
test/misc/mptr.cpp:12:23: error: invalid type in declaration before ‘;’ token
 SBar<G_ptr_to_x> G_bar; // <ERROR>. (This should be legal, and is in clang).
=========================