Re: [committed] libstdc++: Use function object for __decay_copy helper

[Jonathan Wakely <jwakely@redhat.com>]

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On Tue, 15 Jun 2021 at 19:28, Jonathan Wakely wrote:
>
> By changing __cust_access::__decay_copy from a function template to a
> function object we avoid ADL. That means it's fine to call it
> unqualified (the compiler won't waste time doing ADL in associated
> namespaces, and won't try to complete associated types).
>
> This also makes some other minor simplications to other concepts for the
> [range.access] CPOs.
>
> Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/iterator_concepts.h (__cust_access::__decay_copy):
>         Replace with function object.
>         (__cust_access::__member_begin, ___cust_access::_adl_begin): Use
>         __decay_copy unqualified.
>         * include/bits/ranges_base.h (__member_end, __adl_end):
>         Likewise. Use __range_iter_t for type of ranges::begin.
>         (__member_rend): Use correct value category for rbegin argument.
>         (__member_data): Use __decay_copy unqualified.
>         (__begin_data): Use __range_iter_t for type of ranges::begin.

That change makes it impossible to import the header in a module.
Fixed by this patch.

Tested powerpc64le-linux. Pushed to trunk.

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commit c25e3bf87975280a603ff18fba387c6707ce4a95
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jun 16 12:47:32 2021

    libstdc++: Use named struct for __decay_copy
    
    In r12-1486-gcb326a6442f09cb36b05ce556fc91e10bfeb0cf6 I changed
    __decay_copy to be a function object of unnamed class type. This causes
    problems when importing the library headers:
    
    error: conflicting global module declaration 'constexpr const std::ranges::__cust_access::<unnamed struct> std::ranges::__cust_access::__decay_copy'
    
    The fix is to use a named struct instead of an anonymous one.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/iterator_concepts.h (__decay_copy): Name type.

diff --git a/libstdc++-v3/include/bits/iterator_concepts.h b/libstdc++-v3/include/bits/iterator_concepts.h
index d18ae32bf20..11748e5ed7b 100644
--- a/libstdc++-v3/include/bits/iterator_concepts.h
+++ b/libstdc++-v3/include/bits/iterator_concepts.h
@@ -930,7 +930,8 @@ namespace ranges
   {
     using std::__detail::__class_or_enum;
 
-    struct {
+    struct _Decay_copy final
+    {
       template<typename _Tp>
 	constexpr decay_t<_Tp>
 	operator()(_Tp&& __t) const