Bug 59766

Happens too with GCC 4.9 (20140105), as well as when using decltype(auto).

Maybe Adam can have a look.

Sorry.

I can confirm this bug for GCC 4.9.0 20140604 (prerelease).

Created attachment 34538 [details]
ChangeLog entry

Created attachment 34541 [details]
Fix: disable the error for friend declarators.

The fix is simple. Tested and submitted for approval. (I am a registered contributor.)

I don't suppose this warrants a testcase file. If you want to exercise the compiler, here is a more interesting case:


template< typename k >
struct t {
    friend auto leak( t );

    template< typename v >
    struct m {
        friend auto leak( t ) { return v{}; }
    };
};

int main() {
    t< int >::m< char > a;
    decltype( leak( t< int >{} ) ) b;
    static_assert ( sizeof b == 1, "" );
    
    t< int >::m< short > c; // error: redefinition of ‘auto leak(t<int>)’
}

The following still fails on GCC trunk:
    
    struct T {
        friend auto f() { }
    };


Sample command line:

› ~/code/gcc5/bin/g++ --version
g++ (GCC) 5.0.0 20150326 (experimental)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

› ~/code/gcc5/bin/g++ ~/code/hana/test/worksheet.cpp -std=c++1y
[...]: error: non-static data member declared ‘auto’
     friend auto f() { }
                   ^

(In reply to David Krauss from comment #6)
> The fix is simple. Tested and submitted for approval.

Thank you. Did you send it to gcc-patches, with jason AT redhat in Cc: ? I can't find any email from you around that date.

https://gcc.gnu.org/contribute.html

> I don't suppose this warrants a testcase file.

Why not? It is the only way to make sure a later refactoring of the code won't regress on this.

I didn't send it to gcc-patches. It's never been necessary for me before. I suppose I can collect the examples here into a testcase file. In the meantime, anyone else is free to take charge and submit it on their own. The change is just a matter of "don't do that."

(In reply to David Krauss from comment #9)
> I didn't send it to gcc-patches. It's never been necessary for me before.

I appreciate getting direct mail about C++ patches so that I see them faster; I didn't notice this one until today.  Also feel free to ping me if I haven't responded after a week.

I'll check this in after GCC 5 branches.

Author: jason
Date: Tue Apr 14 15:29:27 2015
New Revision: 222095

URL: https://gcc.gnu.org/viewcvs?rev=222095&root=gcc&view=rev
Log:
	PR c++/59766
	* decl.c (grokdeclarator): Do not flag friends with deduced return.

Added:
    trunk/gcc/testsuite/g++.dg/cpp1y/auto-fn26.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/decl.c

Author: jason
Date: Wed Apr 22 20:52:52 2015
New Revision: 222337

URL: https://gcc.gnu.org/viewcvs?rev=222337&root=gcc&view=rev
Log:
	PR c++/59766
	* decl.c (grokdeclarator): Do not flag friends with deduced return.

Added:
    branches/gcc-5-branch/gcc/testsuite/g++.dg/cpp1y/auto-fn26.C
Modified:
    branches/gcc-5-branch/gcc/cp/ChangeLog
    branches/gcc-5-branch/gcc/cp/decl.c

Fixed for 5.2/6.

Author: jason
Date: Thu Apr 23 13:21:06 2015
New Revision: 222365

URL: https://gcc.gnu.org/viewcvs?rev=222365&root=gcc&view=rev
Log:
	PR c++/59766
	* decl.c (grokdeclarator): Do not flag friends with deduced return.

Added:
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/cpp1y/auto-fn26.C
Modified:
    branches/gcc-4_9-branch/gcc/cp/ChangeLog
    branches/gcc-4_9-branch/gcc/cp/decl.c

And 4.9.3.