[WIP] Add cetl::variant

[pavel-kirienko]

This is just an ordinary variant, nothing special here.

Other changes:

• In CETLVaSt, move special member function policies from the optional test into a separate header to make them reusable for the variant test.
• Extend the typelist tools in CETLVaSt.
• Add standard type traits from C++17 (I needed them for the variant): conjunction_v etc.
• Add the overloaded helper class, which is not found in the standard library but is commonly used with visitation. We can move it somewhere if its current place is found unsuitable.
• Add type_traits_ext.hpp with type traits intended for internal use mostly.
• Change the SonarQube invocation to run it against an exception-enabled build to provide full coverage information.
• Doxygen:
  • Ignore the detail namespace.
  • Disable WARN_AS_ERROR because Doxygen v1.9 is unable to parse certain recursive templates correctly; see https://stackoverflow.com/a/77855566/1007777

[pavel-kirienko]

Well, the pull request is finished, except that the CI is still misbehaving. I have already split the tests into six translation units to manage the memory consumption by the compiler. I can split it further if needed but I am not yet confident that this is going to help. The new error from the CI is this:

Received request to deprovision: The request was cancelled by the remote provider

According to this, it may happen due to high CPU/memory utilization: actions/runner-images#7897

[pavel-kirienko]

@thirtytwobits I would like to add an exception for the coverage requirement for variant.hpp because currently it is computed per template instantiation, and the test suite is built to test a small fraction of branches per instantiation, which leads to a very low coverage estimate.

I'm not sure if it warrants an extension of the coverage exclusion list:

CETL/.github/workflows/cetlvast.yml

Line 158 in f58f00f

--define sonar.coverage.exclusions="cetlvast/suites/unittest/**/*,cetlvast/suites/docs/examples/**/*,**/sonar.cpp"

[thirtytwobits]

Approved but could you add this example first:

cetlvast/suites/docs/examples/example_09_variant.cpp

/// @file
/// Example of using cetl::variant.
///
/// @copyright
/// Copyright (C) OpenCyphal Development Team  <opencyphal.org>
/// Copyright Amazon.com Inc. or its affiliates.
/// SPDX-License-Identifier: MIT
///
#include "cetl/pf17/variant.hpp"
#include <string>
#include <algorithm>
#include <cassert>
#include <iostream>
#include <string>

#include <gtest/gtest.h>

TEST(example_09_variant, basic_usage)
{
//! [example_09_basic_usage]
/// This example is taken directly from the [cppreference.com](https://en.cppreference.com/w/cpp/utility/variant)
/// documentation.
    cetl::pf17::variant<int, float> v, w;
    v = 42; // v contains int
    int i = cetl::pf17::get<int>(v);
    assert(42 == i); // succeeds
    w = cetl::pf17::get<int>(v);
    w = cetl::pf17::get<0>(v); // same effect as the previous line
    w = v; // same effect as the previous line

//  cetl::pf17::get<double>(v); // error: no double in [int, float]
//  cetl::pf17::get<3>(v);      // error: valid index values are 0 and 1

    float* result = cetl::pf17::get_if<float>(&w); // w contains int, not float: will return null
    std::cout << "get_if<float>(&w) => " << result << '\n';

    using namespace std::literals;

    cetl::pf17::variant<std::string> x("abc");
    // converting constructors work when unambiguous
    x = "def"; // converting assignment also works when unambiguous

    cetl::pf17::variant<std::string, void const*> y("abc");
    // casts to void const * when passed a char const *
    assert(cetl::pf17::holds_alternative<void const*>(y)); // succeeds
    y = "xyz"s;
    assert(cetl::pf17::holds_alternative<std::string>(y)); // succeeds
//! [example_09_basic_usage]
}

[sonarqubecloud]

Quality Gate failed

Failed conditions
17.3% Coverage on New Code (required ≥ 90%)

See analysis details on SonarCloud