[Bug c++/91309] New: Fails to compile when initializing template argument with immediately-invoked lambda

[beachboy44 at me dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91309

            Bug ID: 91309
           Summary: Fails to compile when initializing template argument
                    with immediately-invoked lambda
           Product: gcc
           Version: 9.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: beachboy44 at me dot com
  Target Milestone: ---

https://godbolt.org/z/8O-ItF

The following code fails to compile:

    template<int>
    struct S {};

    template<int>
    using T = S< []{ return 0; }() >;

    template<int i>
    using U = T<i>;

    using V = U<0>;


error: 'U' does not name a type


However, it compiles when you specify an integer literal as the template
argument to T:

    template<int>
    using U = T<0>;