[Bug c++/97214] New: ICE in lookup_template_class_1, at cp/pt.c:9896

["sfranzen85 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97214

            Bug ID: 97214
           Summary: ICE in lookup_template_class_1, at cp/pt.c:9896
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sfranzen85 at hotmail dot com
  Target Milestone: ---

The following snippet reproduces an error I encountered with lambdas:

struct Foo {
    // void operator()(int) {}

    template<typename T>
    void operator()(T, T)
    {
        auto bar = [this](auto&& v){ operator()(v); };
    }
};

int main ()
{
    Foo{}(0,1);
    return 0;
}

Full error:
../src/main.cpp: In instantiation of ‘void Foo::operator()(T, T) [with T =
int]’:
../src/main.cpp:13:14:   required from here
../src/main.cpp:7:38: internal compiler error: in lookup_template_class_1, at
cp/pt.c:9896
    7 |         auto bar = [this](auto&& v){ operator()(v); };
      |                                      ^~~~~~~~~~

Further observations:
* The error appears regardless of available operator()() overloads;
* It only appears if the function call is unqualified, e.g. (*this)(v) is fine
if the overload exists.

A possibly related error is given using a version of Foo without a function
template:
struct Foo {
    void operator()(int) {}

    void operator()(int a, int)
    {
        auto bar = [this](auto&& v){ operator()(v); };
        bar(a);
    }
};

../src/main.cpp: In instantiation of ‘Foo::operator()(int,
int)::<lambda(auto:1&&)> [with auto:1 = int&]’:
../src/main.cpp:8:14:   required from here
../src/main.cpp:7:48: error: use of ‘Foo::operator()(int,
int)::<lambda(auto:1&&)> [with auto:1 = int&]’ before deduction of ‘auto’
    7 |         auto bar = [this](auto&& v){ operator()(v); };
      |                                      ~~~~~~~~~~^~~

This error similarly only appears with the unqualified call, and also
disappears if the lambda has '-> void'.