[Bug c++/62101] New: deleted definitions of friend functions are rejected

["ville.voutilainen at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62101

            Bug ID: 62101
           Summary: deleted definitions of friend functions are rejected
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ville.voutilainen at gmail dot com

Test:

struct X
{
    friend void f(X, int) = delete;
    friend void f(X, double) {}
};

struct Y;
void g(Y, int);
void g(Y, double);

struct Y
{
    friend void g(Y, int) = delete;
    friend void g(Y, double) {}
};

int main()
{
    X x;
    f(x, 5.0);
    Y y;
    g(y, 5.0);
}

deleted-friend.cpp:3:26: error: can’t initialize friend function ‘f’
  friend void f(X, int) = delete;
                          ^
deleted-friend.cpp:13:26: error: can’t initialize friend function ‘g’
  friend void g(Y, int) = delete;
                          ^

clang accepts the code. There doesn't seem to be any standard wording
forbidding in-class friend definitions that are deleted.
>From gcc-bugs-return-458219-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Tue Aug 12 00:33:42 2014
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From: "potswa at mac dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug preprocessor/58844] [4.8 Regression] ICE with invalid use of ##
Date: Tue, 12 Aug 2014 00:33:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idX844

David Krauss <potswa at mac dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |potswa at mac dot com

--- Comment #9 from David Krauss <potswa at mac dot com> ---
The fix makes the case well-formed. It's not. A sequence of concatenation
operators is not processed as if they were separated by empty parameters. "A ##
## B" concatenates A with the (second) ## to produce an illegal token "A##".
Clang diagnoses it as such.