https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99484
--- Comment #2 from Alexander Lelyakin <alexander.lelyakin at googlemail dot com> --- One more similar, but not the same message; g++ -std=c++20 -fmodules-ts -x c++-system-header any g++ -std=c++20 -fmodules-ts -x c++-system-header vector g++ -std=c++20 -fmodules-ts -x c++-system-header sstream g++ -std=c++20 -fmodules-ts -x c++-system-header shared_mutex g++ -std=c++20 -fmodules-ts -x c++-system-header version g++ -std=c++20 -fmodules-ts -x c++-system-header unordered_set g++ -std=c++20 -fmodules-ts -x c++-system-header string_view g++ -std=c++20 -fmodules-ts -x c++-system-header new g++ -std=c++20 -fmodules-ts -x c++-system-header complex ---- In file included from /usr/local/include/c++/11.0.1/istream:39, from /usr/local/include/c++/11.0.1/sstream:38, of module /usr/local/include/c++/11.0.1/sstream, imported at /usr/local/include/c++/11.0.1/complex:45: /usr/local/include/c++/11.0.1/ostream: In instantiation of ‘struct std::__is_convertible_to_basic_ostream<std::basic_ostream<char>&>’: /usr/local/include/c++/11.0.1/ostream:773:5: required by substitution of ‘template<class _Ostream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_ostream<_Ostream>, std::__is_insertable<typename std::__is_convertible_to_basic_ostream<_Tp>::__ostream_type, const _Tp&, void> >::value, typename std::__is_convertible_to_basic_ostream<_Tp>::__ostream_type>::type std::operator<<(_Ostream&&, const _Tp&) [with _Ostream = std::basic_ostream<char>&; _Tp = std::complex<float>]’ /usr/local/include/c++/11.0.1/complex:1539:70: required from here /usr/local/include/c++/11.0.1/ostream:732:12: internal compiler error: same canonical type node for different types ‘void’ and ‘std::__void_t<decltype (std::__is_convertible_to_basic_ostream_test(declval<typename std::remove_reference<_Tp>::type*>()))>’ 732 | struct __is_convertible_to_basic_ostream | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 0xb7f8dd comptypes(tree_node*, tree_node*, int) ../../gcc/gcc/cp/typeck.c:1554 0xae4bff template_args_equal(tree_node*, tree_node*, bool) ../../gcc/gcc/cp/pt.c:9207 0xae4758 template_args_equal(tree_node*, tree_node*, bool) ../../gcc/gcc/cp/pt.c:9170 0xae4758 comp_template_args(tree_node*, tree_node*, tree_node**, tree_node**, bool) ../../gcc/gcc/cp/pt.c:9254 0xae4758 comp_template_args(tree_node*, tree_node*, tree_node**, tree_node**, bool) ../../gcc/gcc/cp/pt.c:9234 0xaee073 spec_hasher::equal(spec_entry*, spec_entry*) ../../gcc/gcc/cp/pt.c:1725 0xb33b96 hash_table<spec_hasher, false, xcallocator>::verify(spec_entry* const&, unsigned int) ../../gcc/gcc/hash-table.h:1032 0xb3413e hash_table<spec_hasher, false, xcallocator>::find_slot_with_hash(spec_entry* const&, unsigned int, insert_option) ../../gcc/gcc/hash-table.h:968 0xaf101b add_mergeable_specialization(bool, spec_entry*, tree_node*, unsigned int) ../../gcc/gcc/cp/pt.c:30018 0xa6ef5f trees_in::decl_value() ../../gcc/gcc/cp/module.cc:8068 0xa67017 trees_in::tree_node(bool) ../../gcc/gcc/cp/module.cc:9174 0xa6d66b module_state::read_cluster(unsigned int) ../../gcc/gcc/cp/module.cc:14858 0xa6db6d module_state::load_section(unsigned int, binding_slot*) ../../gcc/gcc/cp/module.cc:18129 0xa6dc2f module_state::lazy_load(unsigned int, binding_slot*) ../../gcc/gcc/cp/module.cc:18783 0xa70e67 lazy_load_pendings(tree_node*) ../../gcc/gcc/cp/module.cc:18876 0xb2045f lookup_template_class_1 ../../gcc/gcc/cp/pt.c:9799 0xb227f6 lookup_template_class(tree_node*, tree_node*, tree_node*, tree_node*, int, int) ../../gcc/gcc/cp/pt.c:10237 0xb227f6 tsubst_aggr_type ../../gcc/gcc/cp/pt.c:13572 0xb2f505 instantiate_class_template_1 ../../gcc/gcc/cp/pt.c:11882 0xb30f32 instantiate_class_template(tree_node*) ../../gcc/gcc/cp/pt.c:12264 Please submit a full bug report, with preprocessed source if appropriate. Please include the complete backtrace with any bug report. See <https://gcc.gnu.org/bugs/> for instructions. ---- g++ (GCC) 11.0.1 20210310 (experimental) Copyright (C) 2021 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.