Friend function with requires causes segfault

[Christoph Neumann]

From the versions installed on my machine, the bug occurs in g++ 10.2.0, g++ 10.3.0 and g++ 11.1.0, the only argument in -std=c++2a. The code works on version 9.3.0 with -std=c++2a and -fconcepts. I have also compiled with clang++ 12.0.0 without problems. The bug occurs when two or more classes declare a template friend function with a requires. The return type, number of arguments, number of template parameters, and condition for requires does not make any difference.Example:

class Foo
    {
        template <typename T>
        friend void func() requires true;
    };
    class Bar
    {
        template <typename T>
        friend void func() requires true;
    };

This code results in the following error message:

internal compiler error: Segmentation fault
    9 | friend void func() requires true;
      | ^~~~
0xe30681 internal_error(char const*, ...)
        ???:0
0xf54144 duplicate_decls(tree_node*, tree_node*, bool, bool)
        ???:0
0xf5da9b pushdecl_namespace_level(tree_node*, bool)
        ???:0
0x109001a push_template_decl(tree_node*, bool)
        ???:0
0x151d391 do_friend(tree_node*, tree_node*, tree_node*, tree_node*, overload_flags, bool)
        ???:0
0xfbfc27 grokdeclarator(cp_declarator const*, cp_decl_specifier_seq*, decl_context, int, tree_node**)
        ???:0
0x1003fd4 grokfield(cp_declarator const*, cp_decl_specifier_seq*, tree_node*, bool, tree_node*, tree_node*)
        ???:0
0x1492c03 c_parse_file()
        ???:0
0x148061e c_common_parse_file()
        ???:0
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <file:///usr/share/doc/gcc-11/README.Bugs> for instructions.

On g++-10.x the error is only

internal compiler error: Segmentation fault
    9 | friend void func() requires true;
      | ^~~~
Please submit a full bug report,
with preprocessed source if appropriate.
See <file:///usr/share/doc/gcc-10/README.Bugs> for instructions.

Whether the function actually exists does not have any impact. The error message always points to the second definition, in this case Bar.

[Matthias Klose (doko)]

this works with gcc-11 on Ubuntu 22.04 LTS