The following code raises an ICE on GCC (trunk) and all versions later than and including GCC 11.3. Earlier versions simply fail to instantiate the template. Both Clang and MSVC accept the code (see also this godbolt link: https://godbolt.org/z/x5Ys9sPzx):
```c++
template <typename opt> concept always_true = true;

template <typename ...params>
struct variadic {
    template <typename opt> static void callee() { }
    static void bug() {
        ([]<bool x = always_true<params>>() { 
            if constexpr (x) callee<params>(); 
        }(), ...);
    }
};

int main() { variadic<int>::bug(); }
```

GCC (trunk) on godbolt gives me this stack trace:
<source>: In instantiation of 'variadic<int>::bug()::<lambda()> [with bool x = true]':
<source>:9:10:   required from 'static void variadic<params>::bug() [with params = {int}]'
<source>:13:32:   required from here
<source>:8:44: error: template argument 1 is invalid
    8 |             if constexpr (x) callee<params>();
      |                              ~~~~~~~~~~~~~~^~
<source>:8:44: error: template argument 1 is invalid
<source>:8:44: internal compiler error: in constructor_name_p, at cp/name-lookup.cc:4721
0x23605ae internal_error(char const*, ...)
	???:0
0xa6dd64 fancy_abort(char const*, int, char const*)
	???:0
0xc81ee5 instantiate_decl(tree_node*, bool, bool)
	???:0
0xb5c9e1 maybe_instantiate_decl(tree_node*)
	???:0
0xb5e45e mark_used(tree_node*, int)
	???:0
0xa9da44 build_op_call(tree_node*, vec<tree_node*, va_gc, vl_embed>**, int)
	???:0
0xcc7264 finish_call_expr(tree_node*, vec<tree_node*, va_gc, vl_embed>**, bool, bool, int)
	???:0
0xc79864 tsubst_pack_expansion(tree_node*, tree_node*, int, tree_node*)
	???:0
0xc81ee5 instantiate_decl(tree_node*, bool, bool)
	???:0
0xcad44b instantiate_pending_templates(int)
	???:0
0xb61635 c_parse_final_cleanups()
	???:0
0xd91568 c_common_parse_file()
	???:0