[llvm-bugs] [Bug 48412] New: [Concepts] Constrained 'decltype(auto)' incorrectly treated as 'auto'

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48412

            Bug ID: 48412
           Summary: [Concepts] Constrained 'decltype(auto)' incorrectly
                    treated as 'auto'
           Product: clang
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++2a
          Assignee: unassignedclangbugs at nondot.org
          Reporter: arthur.j.odwyer at gmail.com
                CC: blitzrakete at gmail.com, erik.pilkington at gmail.com,
                    llvm-bugs at lists.llvm.org, richard-llvm at metafoo.co.uk

// https://godbolt.org/z/xxeafq

template<class> concept C = true;
int w;
int& r = w;
C decltype(auto) rr = r;  // rr's type should be 'int&', but is 'int'

That is, 'C decltype(auto) rr = r;' SHOULD be treated exactly like
'decltype(auto) rr = r; static_assert(C<decltype(rr)>);' but in fact Clang is
losing the fact that it's supposed to be a reference type.

Bug 48384 is probably related. From the outside, it feels like Clang's parser
is just treating `C decltype(auto)` as a synonym for `C auto` everywhere it
appears.

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