[llvm-bugs] [Bug 44005] New: lambda expression in template argument fails

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44005

            Bug ID: 44005
           Summary: lambda expression in template argument fails
           Product: clang
           Version: 9.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++2a
          Assignee: unassignedclangbugs at nondot.org
          Reporter: stsp2 at yandex.ru
                CC: blitzrakete at gmail.com, erik.pilkington at gmail.com,
                    llvm-bugs at lists.llvm.org, richard-llvm at metafoo.co.uk

The below example is accepted with g++ -std=c++2a:
---
template <auto O>
struct B {
    static constexpr int off = O();
};

struct A {
    char a;
    B<[](){ return 0; }> b;
};
---

But with clang there is an error:
---
$ clang++ -std=c++2a -o offs1 offs1.cpp 
offs1.cpp:11:7: error: a lambda expression cannot appear in this context
    B<[](){ return 0; }> b;
      ^
offs1.cpp:11:7: error: a non-type template parameter cannot have type
'A::(lambda at offs1.cpp:11:7)'
offs1.cpp:4:16: note: template parameter is declared here
template <auto O>
               ^
2 errors generated.
---

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