[Bug c++/68093] New: [concepts] friend function declarations that differ only by constraints are rejected as redefinitions

[Bug c++/68093] New: [concepts] friend function declarations that differ only by constraints are rejected as redefinitions

[tom at honermann dot net]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68093

            Bug ID: 68093
           Summary: [concepts] friend function declarations that differ
                    only by constraints are rejected as redefinitions
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tom at honermann dot net
  Target Milestone: ---

I believe the following code is intended to be well-formed according to P0121r0
[1].  gcc trunk (r229299) currently rejects it.

$ cat t.cpp
struct S1 {};
struct S2 { using t1 = int; };
template<typename T>
concept bool Has_t1() {
    return requires () { typename T::t1; };
}
template<typename T>
struct TS {
    friend void f(TS) {}
    friend void f(TS) requires Has_t1<T>() {} // Unexpected error: redefinition
};
TS<S1> ts1;
TS<S2> ts2;
auto x = []{
             f(ts1);
             f(ts2);
         };

$ gcc --version
gcc (GCC) 6.0.0 20151025 (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.

$ gcc -c -std=c++1z t.cpp 
t.cpp: In instantiation of ‘struct TS<S1>’:
t.cpp:12:8:   required from here
t.cpp:10:17: error: redefinition of ‘void f(TS<S1>)’
     friend void f(TS) requires Has_t1<T>() {} // Unexpected error:
redefinition
                 ^
t.cpp:9:17: note: ‘void f(TS<S1>)’ previously defined here
     friend void f(TS) {}
                 ^
t.cpp: In instantiation of ‘struct TS<S2>’:
t.cpp:13:8:   required from here
t.cpp:10:17: error: redefinition of ‘void f(TS<S2>)’
     friend void f(TS) requires Has_t1<T>() {} // Unexpected error:
redefinition
                 ^
t.cpp:9:17: note: ‘void f(TS<S2>)’ previously defined here
     friend void f(TS) {}
                 ^

[1]: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0121r0.pdf
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From: "baqwas at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/68094] New: Compiler segmentation fault
Date: Mon, 26 Oct 2015 03:26:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idh094

            Bug ID: 68094
           Summary: Compiler segmentation fault
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: baqwas at gmail dot com
  Target Milestone: ---

Created attachment 36585
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id6585&actioníit
Pre-processed source with error report

Compiler issues segmentation fault for very nominal lines of code as shown in
the attachment. Compiler invoked through Arduino IDE (2:1.0.5+dfsg2-4) running
under Debian Jessie on Raspberry Pi 2 platform.

Arduino IDE under Windows 10 does not exhibit any error.

Arduino installed using standard apt-get install command after the customary
update/upgrade steps. Was able to run Arduino IDE successfully under Debian
Wheezy on same platform.

My apologies if this is a "newbie" error but I did not find any equivalent bugs
reported previously.

[Bug c++/68093] [concepts] friend function declarations that differ only by constraints are rejected as redefinitions

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68093

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
   Target Milestone|---                         |10.0
         Resolution|---                         |FIXED
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Looks like this is fully fixed as of GCC 10.