path: root/src/Progmasoft/Catch3/Internal/Decomposer.hpp

//              Copyright Catch2 Authors
// Distributed under the Boost Software License, Version 1.0.
//   (See accompanying file LICENSE.txt or copy at
//        https://www.boost.org/LICENSE_1_0.txt)

// SPDX-License-Identifier: BSL-1.0
#pragma once

#include <Progmasoft/Catch3/ToString.hpp>
#include <Progmasoft/Catch3/Internal/StringRef.hpp>
#include <Progmasoft/Catch3/Internal/CompareTraits.hpp>
#include <Progmasoft/Catch3/Internal/TestFailureException.hpp>
#include <Progmasoft/Catch3/Internal/LogicalTraits.hpp>
#include <Progmasoft/Catch3/Internal/CompilerCapabilities.hpp>

#include <type_traits>
#include <iosfwd>

/** \file
 * Why does decomposing look the way it does:
 *
 * Conceptually, decomposing is simple. We change `REQUIRE( a == b )` into
 * `Decomposer{} <= a == b`, so that `Decomposer{} <= a` is evaluated first,
 * and our custom operator is used for `a == b`, because `a` is transformed
 * into `ExprLhs<T&>` and then into `BinaryExpr<T&, U&>`.
 *
 * In practice, decomposing ends up a mess, because we have to support
 * various fun things.
 *
 * 1) Types that are only comparable with literal 0, and they do this by
 *    comparing against a magic type with pointer constructor and deleted
 *    other constructors. Example: `REQUIRE((a <=> b) == 0)` in libstdc++
 *
 * 2) Types that are only comparable with literal 0, and they do this by
 *    comparing against a magic type with consteval integer constructor.
 *    Example: `REQUIRE((a <=> b) == 0)` in current MSVC STL.
 *
 * 3) Types that have no linkage, and so we cannot form a reference to
 *    them. Example: some implementations of traits.
 *
 * 4) Starting with C++20, when the compiler sees `a == b`, it also uses
 *    `b == a` when constructing the overload set. For us this means that
 *    when the compiler handles `ExprLhs<T> == b`, it also tries to resolve
 *    the overload set for `b == ExprLhs<T>`.
 *
 * To accommodate these use cases, decomposer ended up rather complex.
 *
 * 1) These types are handled by adding SFINAE overloads to our comparison
 *    operators, checking whether `T == U` are comparable with the given
 *    operator, and if not, whether T (or U) are comparable with literal 0.
 *    If yes, the overload compares T (or U) with 0 literal inline in the
 *    definition.
 *
 *    Note that for extra correctness, we check  that the other type is
 *    either an `int` (literal 0 is captured as `int` by templates), or
 *    a `long` (some platforms use 0L for `NULL` and we want to support
 *    that for pointer comparisons).
 *
 * 2) For these types, `is_foo_comparable<T, int>` is true, but letting
 *    them fall into the overload that actually does `T == int` causes
 *    compilation error. Handling them requires that the decomposition
 *    is `constexpr`, so that P2564R3 applies and the `consteval` from
 *    their accompanying magic type is propagated through the `constexpr`
 *    call stack.
 *
 *    However this is not enough to handle these types automatically,
 *    because our default is to capture types by reference, to avoid
 *    runtime copies. While these references cannot become dangling,
 *    they outlive the constexpr context and thus the default capture
 *    path cannot be actually constexpr.
 *
 *    The solution is to capture these types by value, by explicitly
 *    specializing `Catch::capture_by_value` for them. Catch2 provides
 *    specialization for `std::foo_ordering`s, but users can specialize
 *    the trait for their own types as well.
 *
 * 3) If a type has no linkage, we also cannot capture it by reference.
 *    The solution is once again to capture them by value. We handle
 *    the common cases by using `std::is_arithmetic` and `std::is_enum`
 *    as the default for `Catch::capture_by_value`, but that is only a
 *    some-effort heuristic. These combine to capture all possible bitfield
 *    bases, and also some trait-like types. As with 2), users can
 *    specialize `capture_by_value` for their own types as needed.
 *
 * 4) To support C++20 and make the SFINAE on our decomposing operators
 *    work, the SFINAE has to happen in return type, rather than in
 *    a template type. This is due to our use of logical type traits
 *    (`conjunction`/`disjunction`/`negation`), that we use to workaround
 *    an issue in older (9-) versions of GCC. I still blame C++20 for
 *    this, because without the comparison order switching, the logical
 *    traits could still be used in template type.
 *
 * There are also other side concerns, e.g. supporting both `REQUIRE(a)`
 * and `REQUIRE(a == b)`, or making `REQUIRE_THAT(a, IsEqual(b))` slot
 * nicely into the same expression handling logic, but these are rather
 * straightforward and add only a bit of complexity (e.g. common base
 * class for decomposed expressions).
 */

#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable:4389) // '==' : signed/unsigned mismatch
#pragma warning(disable:4018) // more "signed/unsigned mismatch"
#pragma warning(disable:4312) // Converting int to T* using reinterpret_cast (issue on x64 platform)
#pragma warning(disable:4180) // qualifier applied to function type has no meaning
#pragma warning(disable:4800) // Forcing result to true or false
#endif

#ifdef __clang__
#  pragma clang diagnostic push
#  pragma clang diagnostic ignored "-Wsign-compare"
#  pragma clang diagnostic ignored "-Wnon-virtual-dtor"
#elif defined __GNUC__
#  pragma GCC diagnostic push
#  pragma GCC diagnostic ignored "-Wsign-compare"
#  pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
#endif

#if defined(CATCH_CPP20_OR_GREATER) && __has_include(<compare>)
#  include <compare>
#    if defined( __cpp_lib_three_way_comparison ) && \
            __cpp_lib_three_way_comparison >= 201907L
#      define CATCH_CONFIG_CPP20_COMPARE_OVERLOADS
#    endif
#endif

namespace Catch {

    namespace Detail {
        // This was added in C++20, but we require only C++17.
        template <typename T>
        using RemoveCVRef_t = std::remove_cv_t<std::remove_reference_t<T>>;
    }

    // Note: This is about as much as we can currently reasonably support.
    //       In an ideal world, we could capture by value small trivially
    //       copyable types, but the actual `std::is_trivially_copyable`
    //       trait is a huge mess with standard-violating results on
    //       GCC and Clang, which are unlikely to be fixed soon due to ABI
    //       concerns.
    //       `std::is_scalar` also causes issues due to the `is_pointer`
    //       component, which causes ambiguity issues with (references-to)
    //       function pointer. If those are resolved, we still need to
    //       disambiguate the overload set for arrays, through explicit
    //       overload for references to sized arrays.
    template <typename T>
    struct capture_by_value
        : std::integral_constant<bool,
                                 std::is_arithmetic<T>::value ||
                                     std::is_enum<T>::value> {};

#if defined( CATCH_CONFIG_CPP20_COMPARE_OVERLOADS )
    template <>
    struct capture_by_value<std::strong_ordering> : std::true_type {};
    template <>
    struct capture_by_value<std::weak_ordering> : std::true_type {};
    template <>
    struct capture_by_value<std::partial_ordering> : std::true_type {};
#endif

    template <typename T>
    struct always_false : std::false_type {};

    class ITransientExpression {
        //! Type-erased streaming function for the derived expression
        using StreamFn = void ( * )( void const*, std::ostream& );

        StreamFn m_streamFn;
        bool m_isBinaryExpression;
        bool m_result;

    public:
        constexpr auto isBinaryExpression() const -> bool { return m_isBinaryExpression; }
        constexpr auto getResult() const -> bool { return m_result; }

        constexpr ITransientExpression( StreamFn streamFn,
                                        bool isBinaryExpression,
                                        bool result ):
            m_streamFn( streamFn ),
            m_isBinaryExpression( isBinaryExpression ),
            m_result( result ) {}

        friend std::ostream& operator<<( std::ostream& out,
                                         ITransientExpression const& expr ) {
            expr.m_streamFn( &expr, out );
            return out;
        }
    };

    void formatReconstructedExpression( std::ostream &os, std::string const& lhs, StringRef op, std::string const& rhs );

    template<typename LhsT, typename RhsT>
    class BinaryExpr final : public ITransientExpression {
        LhsT m_lhs;
        StringRef m_op;
        RhsT m_rhs;

        static void streamFn( void const* self, std::ostream& out ) {
            auto const& expr = *static_cast<BinaryExpr const*>(
                static_cast<ITransientExpression const*>( self ) );
            formatReconstructedExpression(
                out,
                Catch::Detail::stringify( expr.m_lhs ),
                expr.m_op,
                Catch::Detail::stringify( expr.m_rhs ) );
        }

    public:
        constexpr BinaryExpr( bool comparisonResult, LhsT lhs, StringRef op, RhsT rhs )
        :   ITransientExpression{ &streamFn, true, comparisonResult },
            m_lhs( lhs ),
            m_op( op ),
            m_rhs( rhs )
        {}
    };

#define CATCH_INTERNAL_DEFINE_BINARY_EXPR_OPERATOR( op )               \
    template <typename LhsT, typename RhsT, typename T>                \
    auto operator op( BinaryExpr<LhsT, RhsT> const&, T )               \
        ->BinaryExpr<LhsT, RhsT const&> const {                        \
        static_assert( always_false<T>::value,                         \
                       "chained comparisons are not supported inside " \
                       "assertions, wrap the expression inside "       \
                       "parentheses, or decompose it" );               \
    }

    /*
     * The operators are **intentionally** not hidden friends.
     *
     * If they were hidden friends, all of them would get stamped out when
     * a `BinaryExpr` is instantiated with a new type. In practice, only
     * few operators are used for each different `BinaryExpr<LhsT, RhsT>`,
     * so this avoids bunch of wasted work.
     */
    CATCH_INTERNAL_DEFINE_BINARY_EXPR_OPERATOR( && )
    CATCH_INTERNAL_DEFINE_BINARY_EXPR_OPERATOR( || )
    CATCH_INTERNAL_DEFINE_BINARY_EXPR_OPERATOR( == )
    CATCH_INTERNAL_DEFINE_BINARY_EXPR_OPERATOR( != )
    CATCH_INTERNAL_DEFINE_BINARY_EXPR_OPERATOR( > )
    CATCH_INTERNAL_DEFINE_BINARY_EXPR_OPERATOR( < )
    CATCH_INTERNAL_DEFINE_BINARY_EXPR_OPERATOR( >= )
    CATCH_INTERNAL_DEFINE_BINARY_EXPR_OPERATOR( <= )

#undef CATCH_INTERNAL_DEFINE_BINARY_EXPR_OPERATOR

    template<typename LhsT>
    class UnaryExpr final : public ITransientExpression {
        LhsT m_lhs;

        static void streamFn( void const* self, std::ostream& os ) {
            auto const& expr = *static_cast<UnaryExpr const*>(
                static_cast<ITransientExpression const*>( self ) );
            os << Catch::Detail::stringify( expr.m_lhs );
        }

    public:
        explicit constexpr UnaryExpr( LhsT lhs )
        :   ITransientExpression{ &streamFn, false, static_cast<bool>(lhs) },
            m_lhs( lhs )
        {}
    };


    template<typename LhsT>
    class ExprLhs {
        LhsT m_lhs;
    public:
        explicit constexpr ExprLhs( LhsT lhs ) : m_lhs( lhs ) {}

        // We rely on reference collapsing if LhsT is already a reference.
        // Used in the out-of-class decomposition operators
        constexpr LhsT& getLhs() { return m_lhs; }

        constexpr auto makeUnaryExpr() const -> UnaryExpr<LhsT> {
            return UnaryExpr<LhsT>{ m_lhs };
        }
    };

/*
 * The comparison operators are **intentionally** not hidden friends.
 *
 * If they were hidden friends, all of them would get stamped out when
 * a `ExprLhs` is instantiated with a new type. In practice, only few
 * operators are used for each different `ExprLhs<T>`, so this avoids
 * a lot of wasted work.
 */
#define CATCH_INTERNAL_DEFINE_EXPRESSION_EQUALITY_OPERATOR( id, op )           \
    template <typename LhsT, typename RhsT>                                    \
    constexpr auto operator op( ExprLhs<LhsT>&& lhs, RhsT&& rhs )              \
        ->std::enable_if_t<                                                    \
            Detail::conjunction<Detail::is_##id##_comparable<LhsT, RhsT>,      \
                                Detail::negation<capture_by_value<             \
                                    Detail::RemoveCVRef_t<RhsT>>>>::value,     \
            BinaryExpr<LhsT, RhsT const&>> {                                   \
        return { static_cast<bool>( lhs.getLhs() op rhs ),                     \
                 lhs.getLhs(),                                                 \
                 #op##_sr,                                                     \
                 rhs };                                                        \
    }                                                                          \
    template <typename LhsT, typename RhsT>                                    \
    constexpr auto operator op( ExprLhs<LhsT>&& lhs, RhsT rhs )                \
        ->std::enable_if_t<                                                    \
            Detail::conjunction<Detail::is_##id##_comparable<LhsT, RhsT>,      \
                                capture_by_value<RhsT>>::value,                \
            BinaryExpr<LhsT, RhsT>> {                                          \
        return { static_cast<bool>( lhs.getLhs() op rhs ),                     \
                 lhs.getLhs(),                                                 \
                 #op##_sr,                                                     \
                 rhs };                                                        \
    }                                                                          \
    template <typename LhsT, typename RhsT>                                    \
    constexpr auto operator op( ExprLhs<LhsT>&& lhs, RhsT rhs )                \
        ->std::enable_if_t<                                                    \
            Detail::conjunction<                                               \
                Detail::negation<Detail::is_##id##_comparable<LhsT, RhsT>>,    \
                Detail::is_eq_0_comparable<LhsT>, /* We allow long because we  \
                                                     want `ptr op NULL` to be  \
                                                     accepted */               \
                Detail::disjunction<std::is_same<RhsT, int>,                   \
                                    std::is_same<RhsT, long>>>::value,         \
            BinaryExpr<LhsT, RhsT>> {                                          \
        if ( rhs != 0 ) { throw_test_failure_exception(); }                    \
        return { static_cast<bool>( lhs.getLhs() op 0 ),                       \
                 lhs.getLhs(),                                                 \
                 #op##_sr,                                                     \
                 rhs };                                                        \
    }                                                                          \
    template <typename LhsT, typename RhsT>                                    \
    constexpr auto operator op( ExprLhs<LhsT>&& lhs, RhsT rhs )                \
        ->std::enable_if_t<                                                    \
            Detail::conjunction<                                               \
                Detail::negation<Detail::is_##id##_comparable<LhsT, RhsT>>,    \
                Detail::is_eq_0_comparable<RhsT>, /* We allow long because we  \
                                                     want `ptr op NULL` to be  \
                                                     accepted */               \
                Detail::disjunction<std::is_same<LhsT, int>,                   \
                                    std::is_same<LhsT, long>>>::value,         \
            BinaryExpr<LhsT, RhsT>> {                                          \
        if ( lhs.getLhs() != 0 ) { throw_test_failure_exception(); }           \
        return { static_cast<bool>( 0 op rhs ), lhs.getLhs(), #op##_sr, rhs }; \
    }

    CATCH_INTERNAL_DEFINE_EXPRESSION_EQUALITY_OPERATOR( eq, == )
    CATCH_INTERNAL_DEFINE_EXPRESSION_EQUALITY_OPERATOR( ne, != )

#undef CATCH_INTERNAL_DEFINE_EXPRESSION_EQUALITY_OPERATOR

#define CATCH_INTERNAL_DEFINE_EXPRESSION_COMPARISON_OPERATOR( id, op )         \
    template <typename LhsT, typename RhsT>                                    \
    constexpr auto operator op( ExprLhs<LhsT>&& lhs, RhsT&& rhs )              \
        ->std::enable_if_t<                                                    \
            Detail::conjunction<Detail::is_##id##_comparable<LhsT, RhsT>,      \
                                Detail::negation<capture_by_value<             \
                                    Detail::RemoveCVRef_t<RhsT>>>>::value,     \
            BinaryExpr<LhsT, RhsT const&>> {                                   \
        return { static_cast<bool>( lhs.getLhs() op rhs ),                     \
                 lhs.getLhs(),                                                 \
                 #op##_sr,                                                     \
                 rhs };                                                        \
    }                                                                          \
    template <typename LhsT, typename RhsT>                                    \
    constexpr auto operator op( ExprLhs<LhsT>&& lhs, RhsT rhs )                \
        ->std::enable_if_t<                                                    \
            Detail::conjunction<Detail::is_##id##_comparable<LhsT, RhsT>,      \
                                capture_by_value<RhsT>>::value,                \
            BinaryExpr<LhsT, RhsT>> {                                          \
        return { static_cast<bool>( lhs.getLhs() op rhs ),                     \
                 lhs.getLhs(),                                                 \
                 #op##_sr,                                                     \
                 rhs };                                                        \
    }                                                                          \
    template <typename LhsT, typename RhsT>                                    \
    constexpr auto operator op( ExprLhs<LhsT>&& lhs, RhsT rhs )                \
        ->std::enable_if_t<                                                    \
            Detail::conjunction<                                               \
                Detail::negation<Detail::is_##id##_comparable<LhsT, RhsT>>,    \
                Detail::is_##id##_0_comparable<LhsT>,                          \
                std::is_same<RhsT, int>>::value,                               \
            BinaryExpr<LhsT, RhsT>> {                                          \
        if ( rhs != 0 ) { throw_test_failure_exception(); }                    \
        return { static_cast<bool>( lhs.getLhs() op 0 ),                       \
                 lhs.getLhs(),                                                 \
                 #op##_sr,                                                     \
                 rhs };                                                        \
    }                                                                          \
    template <typename LhsT, typename RhsT>                                    \
    constexpr auto operator op( ExprLhs<LhsT>&& lhs, RhsT rhs )                \
        ->std::enable_if_t<                                                    \
            Detail::conjunction<                                               \
                Detail::negation<Detail::is_##id##_comparable<LhsT, RhsT>>,    \
                Detail::is_##id##_0_comparable<RhsT>,                          \
                std::is_same<LhsT, int>>::value,                               \
            BinaryExpr<LhsT, RhsT>> {                                          \
        if ( lhs.getLhs() != 0 ) { throw_test_failure_exception(); }           \
        return { static_cast<bool>( 0 op rhs ), lhs.getLhs(), #op##_sr, rhs }; \
    }

    CATCH_INTERNAL_DEFINE_EXPRESSION_COMPARISON_OPERATOR( lt, < )
    CATCH_INTERNAL_DEFINE_EXPRESSION_COMPARISON_OPERATOR( le, <= )
    CATCH_INTERNAL_DEFINE_EXPRESSION_COMPARISON_OPERATOR( gt, > )
    CATCH_INTERNAL_DEFINE_EXPRESSION_COMPARISON_OPERATOR( ge, >= )

#undef CATCH_INTERNAL_DEFINE_EXPRESSION_COMPARISON_OPERATOR

#define CATCH_INTERNAL_DEFINE_EXPRESSION_OPERATOR( op )            \
    template <typename LhsT, typename RhsT>                        \
    constexpr auto operator op( ExprLhs<LhsT>&& lhs, RhsT&& rhs )  \
        ->std::enable_if_t<                                        \
            !capture_by_value<Detail::RemoveCVRef_t<RhsT>>::value, \
            BinaryExpr<LhsT, RhsT const&>> {                       \
        return { static_cast<bool>( lhs.getLhs() op rhs ),         \
                 lhs.getLhs(),                                     \
                 #op##_sr,                                         \
                 rhs };                                            \
    }                                                              \
    template <typename LhsT, typename RhsT>                        \
    constexpr auto operator op( ExprLhs<LhsT>&& lhs, RhsT rhs )    \
        ->std::enable_if_t<capture_by_value<RhsT>::value,          \
                           BinaryExpr<LhsT, RhsT>> {               \
        return { static_cast<bool>( lhs.getLhs() op rhs ),         \
                 lhs.getLhs(),                                     \
                 #op##_sr,                                         \
                 rhs };                                            \
    }

    CATCH_INTERNAL_DEFINE_EXPRESSION_OPERATOR( | )
    CATCH_INTERNAL_DEFINE_EXPRESSION_OPERATOR( & )
    CATCH_INTERNAL_DEFINE_EXPRESSION_OPERATOR( ^)

#undef CATCH_INTERNAL_DEFINE_EXPRESSION_OPERATOR

    template <typename LhsT, typename RhsT>
    auto operator&&( ExprLhs<LhsT>&&, RhsT&& )
        -> BinaryExpr<LhsT, RhsT const&> {
        static_assert(
            always_false<RhsT>::value,
            "operator&& is not supported inside assertions, "
            "wrap the expression inside parentheses, or decompose it" );
    }

    template <typename LhsT, typename RhsT>
    auto operator||( ExprLhs<LhsT>&&, RhsT&& )
        -> BinaryExpr<LhsT, RhsT const&> {
        static_assert(
            always_false<RhsT>::value,
            "operator|| is not supported inside assertions, "
            "wrap the expression inside parentheses, or decompose it" );
    }


    struct Decomposer {
        template <typename T,
                  std::enable_if_t<!capture_by_value<Detail::RemoveCVRef_t<T>>::value,
                      int> = 0>
        constexpr friend auto operator <= ( Decomposer &&, T && lhs ) -> ExprLhs<T const&> {
            return ExprLhs<const T&>{ lhs };
        }

        template <typename T,
                  std::enable_if_t<capture_by_value<T>::value, int> = 0>
        constexpr friend auto operator <= ( Decomposer &&, T value ) -> ExprLhs<T> {
            return ExprLhs<T>{ value };
        }
    };

} // end namespace Catch

#ifdef _MSC_VER
#pragma warning(pop)
#endif
#ifdef __clang__
#  pragma clang diagnostic pop
#elif defined __GNUC__
#  pragma GCC diagnostic pop
#endif