From cf61803f59cf29251bd37c5e6e012f350b46040f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A9=20Bargull?= <andre.bargull@gmail.com>
Date: Sat, 28 Mar 2020 13:57:12 +0000
Subject: [PATCH] Bug 1625138 - Part 5: Replace mozilla::IsDefaultConstructible
 with std::is_default_constructible. r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D68359
---
 mfbt/Result.h                 |  4 +-
 mfbt/TypeTraits.h             | 38 --------------
 mfbt/tests/TestTypeTraits.cpp | 99 -----------------------------------
 3 files changed, 2 insertions(+), 139 deletions(-)

diff --git a/mfbt/Result.h b/mfbt/Result.h
index d061a5e137a9c..b02638e78839d 100644
--- a/mfbt/Result.h
+++ b/mfbt/Result.h
@@ -272,8 +272,8 @@ struct SelectResultImpl {
           ? PackingStrategy::NullIsOk
           : (detail::HasFreeLSB<V>::value && detail::HasFreeLSB<E>::value)
                 ? PackingStrategy::LowBitTagIsError
-                : (IsDefaultConstructible<V>::value &&
-                   IsDefaultConstructible<E>::value &&
+                : (std::is_default_constructible_v<V> &&
+                   std::is_default_constructible_v<E> &&
                    IsPackableVariant<V, E>::value)
                       ? PackingStrategy::PackedVariant
                       : PackingStrategy::Variant;
diff --git a/mfbt/TypeTraits.h b/mfbt/TypeTraits.h
index a2fa5df38b845..cb046e8ffd5f0 100644
--- a/mfbt/TypeTraits.h
+++ b/mfbt/TypeTraits.h
@@ -468,44 +468,6 @@ struct IsUnsigned : detail::IsUnsignedHelper<T> {};
 
 namespace detail {
 
-struct DoIsDefaultConstructibleImpl {
-  template <typename T, typename = decltype(T())>
-  static TrueType test(int);
-  template <typename T>
-  static FalseType test(...);
-};
-
-template <typename T>
-struct IsDefaultConstructibleImpl : public DoIsDefaultConstructibleImpl {
-  typedef decltype(test<T>(0)) Type;
-};
-
-}  // namespace detail
-
-/**
- * IsDefaultConstructible determines whether a type has a public default
- * constructor.
- *
- * struct S0 {};                    // Implicit default constructor.
- * struct S1 { S1(); };
- * struct S2 { explicit S2(int); }; // No implicit default constructor when
- *                                  // another one is present.
- * struct S3 { S3() = delete; };
- * class C4 { C4(); };              // Default constructor is private.
- *
- * mozilla::IsDefaultConstructible<int>::value is true;
- * mozilla::IsDefaultConstructible<S0>::value is true;
- * mozilla::IsDefaultConstructible<S1>::value is true;
- * mozilla::IsDefaultConstructible<S2>::value is false;
- * mozilla::IsDefaultConstructible<S3>::value is false;
- * mozilla::IsDefaultConstructible<S4>::value is false.
- */
-template <typename T>
-struct IsDefaultConstructible
-    : public detail::IsDefaultConstructibleImpl<T>::Type {};
-
-namespace detail {
-
 struct DoIsDestructibleImpl {
   template <typename T, typename = decltype(DeclVal<T&>().~T())>
   static TrueType test(int);
diff --git a/mfbt/tests/TestTypeTraits.cpp b/mfbt/tests/TestTypeTraits.cpp
index 21d6a18eea145..5b618f6b816f7 100644
--- a/mfbt/tests/TestTypeTraits.cpp
+++ b/mfbt/tests/TestTypeTraits.cpp
@@ -18,7 +18,6 @@ using mozilla::DeclVal;
 using mozilla::IsArray;
 using mozilla::IsClass;
 using mozilla::IsConvertible;
-using mozilla::IsDefaultConstructible;
 using mozilla::IsDestructible;
 using mozilla::IsFunction;
 using mozilla::IsPointer;
@@ -209,104 +208,6 @@ static_assert(!IsSigned<NotIntConstructible>::value,
 static_assert(!IsUnsigned<NotIntConstructible>::value,
               "non-arithmetic types are not unsigned");
 
-struct TrivialCtor0 {};
-struct TrivialCtor1 {
-  int mX;
-};
-
-struct DefaultCtor0 {
-  DefaultCtor0() = default;
-};
-struct DefaultCtor1 {
-  DefaultCtor1() = default;
-};
-struct DefaultCtor2 {
-  DefaultCtor2() = default;
-  explicit DefaultCtor2(int) {}
-};
-
-struct NoDefaultCtor0 {
-  explicit NoDefaultCtor0(int) {}
-};
-struct NoDefaultCtor1 {
-  NoDefaultCtor1() = delete;
-};
-
-class PrivateCtor0 {
-  PrivateCtor0() = default;
-};
-class PrivateCtor1 {
-  PrivateCtor1() = default;
-};
-
-enum EnumCtor0 {};
-enum EnumCtor1 : int {};
-
-enum class EnumClassCtor0 {};
-enum class EnumClassCtor1 : int {};
-
-union UnionCtor0 {};
-union UnionCtor1 {
-  int mX;
-};
-
-union UnionCustomCtor0 {
-  explicit UnionCustomCtor0(int) {}
-};
-union UnionCustomCtor1 {
-  int mX;
-  explicit UnionCustomCtor1(int aX) : mX(aX) {}
-};
-
-static_assert(IsDefaultConstructible<int>::value,
-              "integral type is default-constructible");
-
-static_assert(IsDefaultConstructible<TrivialCtor0>::value,
-              "trivial constructor class 0 is default-constructible");
-static_assert(IsDefaultConstructible<TrivialCtor1>::value,
-              "trivial constructor class 1 is default-constructible");
-
-static_assert(IsDefaultConstructible<DefaultCtor0>::value,
-              "default constructor class 0 is default-constructible");
-static_assert(IsDefaultConstructible<DefaultCtor1>::value,
-              "default constructor class 1 is default-constructible");
-static_assert(IsDefaultConstructible<DefaultCtor2>::value,
-              "default constructor class 2 is default-constructible");
-
-static_assert(!IsDefaultConstructible<NoDefaultCtor0>::value,
-              "no default constructor class is not default-constructible");
-static_assert(!IsDefaultConstructible<NoDefaultCtor1>::value,
-              "deleted default constructor class is not default-constructible");
-
-static_assert(
-    !IsDefaultConstructible<PrivateCtor0>::value,
-    "private default constructor class 0 is not default-constructible");
-static_assert(
-    !IsDefaultConstructible<PrivateCtor1>::value,
-    "private default constructor class 1 is not default-constructible");
-
-static_assert(IsDefaultConstructible<EnumCtor0>::value,
-              "enum constructor 0 is default-constructible");
-static_assert(IsDefaultConstructible<EnumCtor1>::value,
-              "enum constructor 1 is default-constructible");
-
-static_assert(IsDefaultConstructible<EnumClassCtor0>::value,
-              "enum class constructor 0 is default-constructible");
-static_assert(IsDefaultConstructible<EnumClassCtor1>::value,
-              "enum class constructor 1 is default-constructible");
-
-static_assert(IsDefaultConstructible<UnionCtor0>::value,
-              "union constructor 0 is default-constructible");
-static_assert(IsDefaultConstructible<UnionCtor1>::value,
-              "union constructor 1 is default-constructible");
-
-static_assert(
-    !IsDefaultConstructible<UnionCustomCtor0>::value,
-    "union with custom 1-arg constructor 0 is not default-constructible");
-static_assert(
-    !IsDefaultConstructible<UnionCustomCtor1>::value,
-    "union with custom 1-arg constructor 1 is not default-constructible");
-
 class PublicDestructible {
  public:
   ~PublicDestructible();