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Fix the implementation of OnlyLiteralZero (#1420)
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This patch changes the implementation of OnlyLiteralZero to only fail if the second overload is chosen, instead of failing during overload resolution.

This patch cherry-picks 2de126c.

Fixes #1419
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@derekmauro
derekmauro authored Mar 27, 2023
1 parent c8a2f92 commit b971ac5
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Showing 2 changed files with 60 additions and 61 deletions.
2 changes: 1 addition & 1 deletion absl/base/config.h
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Original file line number Diff line number Diff line change
Expand Up @@ -112,7 +112,7 @@
// LTS releases can be obtained from
// https://github.com/abseil/abseil-cpp/releases.
#define ABSL_LTS_RELEASE_VERSION 20230125
#define ABSL_LTS_RELEASE_PATCH_LEVEL 1
#define ABSL_LTS_RELEASE_PATCH_LEVEL 2

// Helper macro to convert a CPP variable to a string literal.
#define ABSL_INTERNAL_DO_TOKEN_STR(x) #x
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119 changes: 59 additions & 60 deletions absl/types/compare.h
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Original file line number Diff line number Diff line change
Expand Up @@ -44,29 +44,28 @@ namespace compare_internal {

using value_type = int8_t;

template <typename T>
struct Fail {
static_assert(sizeof(T) < 0, "Only literal `0` is allowed.");
};
class OnlyLiteralZero {
// A private type which cannot be named to explicitly cast to it.
struct MatchLiteralZero;

// We need the NullPtrT template to avoid triggering the modernize-use-nullptr
// ClangTidy warning in user code.
template <typename NullPtrT = std::nullptr_t>
struct OnlyLiteralZero {
constexpr OnlyLiteralZero(NullPtrT) noexcept {} // NOLINT
public:
// Accept only literal zero since it can be implicitly converted to a pointer
// type. nullptr constants will be caught by the other constructor which
// accepts a nullptr_t.
constexpr OnlyLiteralZero(MatchLiteralZero *) noexcept {} // NOLINT

// Fails compilation when `nullptr` or integral type arguments other than
// `int` are passed. This constructor doesn't accept `int` because literal `0`
// has type `int`. Literal `0` arguments will be implicitly converted to
// `std::nullptr_t` and accepted by the above constructor, while other `int`
// arguments will fail to be converted and cause compilation failure.
template <
typename T,
typename = typename std::enable_if<
std::is_same<T, std::nullptr_t>::value ||
(std::is_integral<T>::value && !std::is_same<T, int>::value)>::type,
typename = typename Fail<T>::type>
OnlyLiteralZero(T); // NOLINT
template <typename T, typename = typename std::enable_if<
std::is_same<T, std::nullptr_t>::value ||
(std::is_integral<T>::value &&
!std::is_same<T, int>::value)>::type>
OnlyLiteralZero(T) { // NOLINT
static_assert(sizeof(T) < 0, "Only literal `0` is allowed.");
}
};

enum class eq : value_type {
Expand Down Expand Up @@ -163,18 +162,18 @@ class weak_equality

// Comparisons
friend constexpr bool operator==(
weak_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
weak_equality v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ == 0;
}
friend constexpr bool operator!=(
weak_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
weak_equality v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ != 0;
}
friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator==(compare_internal::OnlyLiteralZero,
weak_equality v) noexcept {
return 0 == v.value_;
}
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero,
weak_equality v) noexcept {
return 0 != v.value_;
}
Expand Down Expand Up @@ -214,18 +213,18 @@ class strong_equality
}
// Comparisons
friend constexpr bool operator==(
strong_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
strong_equality v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ == 0;
}
friend constexpr bool operator!=(
strong_equality v, compare_internal::OnlyLiteralZero<>) noexcept {
strong_equality v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ != 0;
}
friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator==(compare_internal::OnlyLiteralZero,
strong_equality v) noexcept {
return 0 == v.value_;
}
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero,
strong_equality v) noexcept {
return 0 != v.value_;
}
Expand Down Expand Up @@ -277,50 +276,50 @@ class partial_ordering
}
// Comparisons
friend constexpr bool operator==(
partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.is_ordered() && v.value_ == 0;
}
friend constexpr bool operator!=(
partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return !v.is_ordered() || v.value_ != 0;
}
friend constexpr bool operator<(
partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.is_ordered() && v.value_ < 0;
}
friend constexpr bool operator<=(
partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.is_ordered() && v.value_ <= 0;
}
friend constexpr bool operator>(
partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.is_ordered() && v.value_ > 0;
}
friend constexpr bool operator>=(
partial_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
partial_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.is_ordered() && v.value_ >= 0;
}
friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator==(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return v.is_ordered() && 0 == v.value_;
}
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return !v.is_ordered() || 0 != v.value_;
}
friend constexpr bool operator<(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator<(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return v.is_ordered() && 0 < v.value_;
}
friend constexpr bool operator<=(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator<=(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return v.is_ordered() && 0 <= v.value_;
}
friend constexpr bool operator>(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator>(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return v.is_ordered() && 0 > v.value_;
}
friend constexpr bool operator>=(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator>=(compare_internal::OnlyLiteralZero,
partial_ordering v) noexcept {
return v.is_ordered() && 0 >= v.value_;
}
Expand Down Expand Up @@ -369,50 +368,50 @@ class weak_ordering
}
// Comparisons
friend constexpr bool operator==(
weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ == 0;
}
friend constexpr bool operator!=(
weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ != 0;
}
friend constexpr bool operator<(
weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ < 0;
}
friend constexpr bool operator<=(
weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ <= 0;
}
friend constexpr bool operator>(
weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ > 0;
}
friend constexpr bool operator>=(
weak_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
weak_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ >= 0;
}
friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator==(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 == v.value_;
}
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 != v.value_;
}
friend constexpr bool operator<(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator<(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 < v.value_;
}
friend constexpr bool operator<=(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator<=(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 <= v.value_;
}
friend constexpr bool operator>(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator>(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 > v.value_;
}
friend constexpr bool operator>=(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator>=(compare_internal::OnlyLiteralZero,
weak_ordering v) noexcept {
return 0 >= v.value_;
}
Expand Down Expand Up @@ -468,50 +467,50 @@ class strong_ordering
}
// Comparisons
friend constexpr bool operator==(
strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ == 0;
}
friend constexpr bool operator!=(
strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ != 0;
}
friend constexpr bool operator<(
strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ < 0;
}
friend constexpr bool operator<=(
strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ <= 0;
}
friend constexpr bool operator>(
strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ > 0;
}
friend constexpr bool operator>=(
strong_ordering v, compare_internal::OnlyLiteralZero<>) noexcept {
strong_ordering v, compare_internal::OnlyLiteralZero) noexcept {
return v.value_ >= 0;
}
friend constexpr bool operator==(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator==(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 == v.value_;
}
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator!=(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 != v.value_;
}
friend constexpr bool operator<(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator<(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 < v.value_;
}
friend constexpr bool operator<=(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator<=(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 <= v.value_;
}
friend constexpr bool operator>(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator>(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 > v.value_;
}
friend constexpr bool operator>=(compare_internal::OnlyLiteralZero<>,
friend constexpr bool operator>=(compare_internal::OnlyLiteralZero,
strong_ordering v) noexcept {
return 0 >= v.value_;
}
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