[Bug c++/107278] fails to correctly parse template default function declarations.

["ky4ct at arrl dot net" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107278

Jonathan <ky4ct at arrl dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

--- Comment #8 from Jonathan <ky4ct at arrl dot net> ---
Proposed resolution (November, 2017)

    Change 11.4.5 [class.ctor] paragraph 1 as follows:

        ...and the id-expression has one of the following forms:

            in a member-declaration that belongs to the member-specification of
a class or class template but is not a friend declaration (11.8.4
[class.friend]), the id-expression is the injected-class-name ( Clause 11
[class]) of the immediately-enclosing class; entity or

            in a member-declaration that belongs to the member-specification of
a class template but is not a friend declaration, the id-expression is a
class-name that names the current instantiation (13.8.3.2 [temp.dep.type]) of
the immediately-enclosing class template; or

            in a declaration at namespace scope or in a friend declaration, the
id-expression is a qualified-id that names a constructor (6.5.5.2
[class.qual]).

    Change 11.4.7 [class.dtor] paragraph 1 as follows:

        ...and the id-expression has one of the following forms:

            in a member-declaration that belongs to the member-specification of
a class or class template but is not a friend declaration (11.8.4
[class.friend]), the id-expression is ~class-name and the class-name is the
injected-class-name (Clause 11 [class]) of the immediately-enclosing class;
entity or

            in a member-declaration that belongs to the member-specification of
a class template but is not a friend declaration, the id-expression is
~class-name and the class-name names the current instantiation (13.8.3.2
[temp.dep.type]) of the immediately-enclosing class template; or

            in a declaration at namespace scope or in a friend declaration, the
id-expression is nested-name-specifier ~class-name and the class-name names the
same class as the nested-name-specifier.

    Add the following as a new paragraph in C.2 [diff.cpp17]:

        C.5.x Clause 15: Special member functions [diff.cpp17.special]

        Affected subclauses: 11.4.5 [class.ctor], 11.4.7 [class.dtor]
        Change: A simple-template-id is no longer valid as the declarator-id of
a constructor or destructor.
        Rationale: Remove potentially error-prone option for redundancy.
        Effect on original feature: Valid C++ 2017 code may fail to compile.

          template<class T>
          struct A {
            A<T>();  // error: simple-template-id not allowed for constructor
            A(int);  // OK, injected-class-name used
            ~A<T>(); // error: simple-template-id not allowed for destructor
          };

(Note that this resolution is a change for C++20, NOT a defect report against
C++17 and earlier versions.)