Best conversion selector is not behaving as expected in some scenarios

[pavel-kirienko]

Moving from https://github.com/OpenCyphal-Garage/libcyphal/issues/355

Running ./build-tools/bin/verify.py release on "ts22.4.7" docker image on macOS M2 machine fails with following on line # 104:

static_assert(best_conversion_index_v<std::is_unsigned, long, char, long, unsigned long> == 2, "");

[26/108] Building CXX object suites/unittest/CMakeFiles/test_type_traits_ext__googletest_objlib.dir/test_type_traits_ext.cpp.o
FAILED: suites/unittest/CMakeFiles/test_type_traits_ext__googletest_objlib.dir/test_type_traits_ext.cpp.o
/usr/bin/g++ -DCETL_VERSION=\"1.3.0\" -I/repo/cetlvast/include -I/repo/include -I/repo/cetlvast/build_external/o1heap/o1heap -isystem /repo/cetlvast/build_external/googletest/googletest/include -isystem /repo/cetlvast/build_external/googletest/googletest -isystem /repo/cetlvast/build_external/googletest/googlemock/include -isystem /repo/cetlvast/build_external/googletest/googlemock -g -pedantic -Wall -Wextra -Werror -Wfloat-equal -Wconversion -Wunused-parameter -Wunused-variable -Wunused-value -Wcast-align -Wmissing-declarations -Wmissing-field-initializers -Wdouble-promotion -Wswitch-enum -Wtype-limits -Wno-error=array-bounds -Wsign-conversion -Wsign-promo -Wold-style-cast -Wzero-as-null-pointer-constant -Wnon-virtual-dtor -Woverloaded-virtual -O0 -DDEBUG -ggdb -std=c++14 -MD -MT suites/unittest/CMakeFiles/test_type_traits_ext__googletest_objlib.dir/test_type_traits_ext.cpp.o -MF suites/unittest/CMakeFiles/test_type_traits_ext__googletest_objlib.dir/test_type_traits_ext.cpp.o.d -o suites/unittest/CMakeFiles/test_type_traits_ext__googletest_objlib.dir/test_type_traits_ext.cpp.o -c /repo/cetlvast/suites/unittest/test_type_traits_ext.cpp
/repo/cetlvast/suites/unittest/test_type_traits_ext.cpp:104:90: error: static assertion failed
  104 | static_assert(best_conversion_index_v<std::is_unsigned, long, char, long, unsigned long> == 2, "");
      |               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
/repo/cetlvast/suites/unittest/test_type_traits_ext.cpp:104:90: note: the comparison reduces to ‘(18446744073709551615 == 2)’
[28/108] Building CXX object suites/unittest/CMakeFiles/test_pf17_variant_other__googletest_objlib.dir/test_pf17_variant_other.cpp.o
ninja: build stopped: subcommand failed.
root@7b9e4d01cc28:/repo# uname -a
Linux 7b9e4d01cc28 6.6.22-linuxkit #1 SMP Fri Mar 29 12:21:27 UTC 2024 aarch64 aarch64 aarch64 GNU/Linux

[pavel-kirienko]

Another one with GCC v7.3.1:

include/cetl/pf17/variant.hpp:723:1: error: static assertion failed: self-test failure
static_assert(best_converting_ctor_index_v<float, long, float, bool> == 1, "self-test failure");
^~~~~~~~~~~~~ 

[lydia-at-amazon]

Some more examples in unit tests with GCC v7.3.1:

cetlvast/suites/unittest/test_type_traits_ext.cpp:115:1: error: static assertion failed
static_assert(best_conversion_index_v<partial<is_convertible_without_narrowing, char>::template type, char, foo, int> ==
^~~~~~~~~~~~~
cetlvast/suites/unittest/test_type_traits_ext.cpp:118:1: error: static assertion failed
static_assert(best_conversion_index_v<partial<is_convertible_without_narrowing, char>::template type, char, foo> == bad,
^~~~~~~~~~~~~ 

[lydia-at-amazon]

More examples in variant.hpp:

include/cetl/pf17/variant.hpp:724:1: error: static assertion failed: self-test failure
static_assert(best_converting_ctor_index_v<double, long, float, double, bool> == 2, "self-test failure");
^~~~~~~~~~~~~

include/cetl/pf17/variant.hpp:740:1: error: static assertion failed: self-test failure
static_assert(best_converting_assignment_index_v<float, long, float, bool> == 1, "self-test failure");
^~~~~~~~~~~~~

include/cetl/pf17/variant.hpp:741:1: error: static assertion failed: self-test failure
static_assert(best_converting_assignment_index_v<double, long, float, double, bool> == 2, "self-test failure");
^~~~~~~~~~~~~