[Bug c++/60679] New: class specialization not instantiated even though it is a better match than the primary template

[Bug c++/60679] New: class specialization not instantiated even though it is a better match than the primary template

[filip.roseen at gmail dot com]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60679

            Bug ID: 60679
           Summary: class specialization not instantiated even though it
                    is a better match than the primary template
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: filip.roseen at gmail dot com

Created attachment 32463
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32463&action=edit
testcase.cpp

template<int...> struct A { };        // (A)

template<char X, char Y>
struct A<X, Y> { typedef int type; }; // (B)

int main () {
  (void) A<0, 0>::type { };
}

-------------------------------------------------------------------------------

testcase.cpp: In function ‘int main()’:
testcase.cpp:7:10: error: ‘type’ is not a member of ‘A<0, 0>’
   (void) A<0, 0>::type { };
          ^
-------------------------------------------------------------------------------

Note: `clang` correctly accepts `testcase.cpp`.

-------------------------------------------------------------------------------

This is how it should look, but gcc fails on step 4);

 1. first our primary template `(A)` is looked up, and our template
    arguments are deduced from those specified for this primary template

 2. we then look for specializations, `(B)` should be found

 3. `(B)` is more specialized than our primary template, proceed

 4. `(B)` should be selected if no narrowing-conversion applies to
    instantiating it, which is true; `int { 0 }` fits inside `char`

    Note: A non-narrowing conversion can be proved since `0` is a
          constant-expression and can fit inside `char`, see
          [dcl.init.list]p7

 5. `(B)` is the best candidate, instantiate it

-------------------------------------------------------------------------------


[temp.class.spec.match]p4:

  > The templates arguments of a specializaton are deduced from the arguments
  > of the primary template.


[temp.class.spec]p6 states the following:

  > Partial specializations declarations themselves are not found by name
  > lookup. Rather, when the primary template name is used, any
  > previously-declared partial specializations of the primary template
  > are also considered.

-------------------------------------------------------------------------------
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From: "filip.roseen at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/60680] New: unqalified-id expected, gcc fails to diagnose and accepts invalid
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`680

            Bug ID: 60680
           Summary: unqalified-id expected, gcc fails to diagnose and
                    accepts invalid
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: filip.roseen at gmail dot com

Created attachment 32464
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id2464&actioníit
testcase.cpp

int main () {
  int(*) = 0;
}

----------------------------------------------------------------------------------

The above compiles but the above is not legal according to any section of the
Standard. `clang` correctly throws out a diagnostic saying that the line in
question is ill-formed.

There are many variations on the above that gcc happily accepts, such as:

`auto(*)(int) = 0`, `auto(*)() = 0`, etc, etc.

[Bug c++/60679] class specialization not instantiated even though it is a better match than the primary template

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60679

Ville Voutilainen <ville.voutilainen at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-12-14
                 CC|                            |ville.voutilainen at gmail dot com
     Ever confirmed|0                           |1
      Known to fail|                            |4.8.2, 4.9.1, 5.0

[Bug c++/60679] class specialization not instantiated even though it is a better match than the primary template

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60679

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |SUSPENDED

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
yes it does look like that CWG which is still active so suspending.

[Bug c++/60679] [DR1647] class specialization not instantiated even though it is a better match than the primary template

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60679

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1647

[Bug c++/60679] [DR1647] class specialization not instantiated even though it is a better match than the primary template

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60679

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ghabriel.nunes at hotmail dot com

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 87108 has been marked as a duplicate of this bug. ***

[Bug c++/60679] [DR1647] class specialization not instantiated even though it is a better match than the primary template

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60679

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ray@klipp-lischner.net

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 83426 has been marked as a duplicate of this bug. ***

[Bug c++/60679] [DR1647] class specialization not instantiated even though it is a better match than the primary template

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60679

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fchelnokov at gmail dot com

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 104043 has been marked as a duplicate of this bug. ***

[Bug c++/60679] [DR1647] class specialization not instantiated even though it is a better match than the primary template

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60679

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hokein.wu at gmail dot com

--- Comment #7 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 114378 has been marked as a duplicate of this bug. ***