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chromium/chromium-65.0.3325.146-Fix-...

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7 years ago
diff -up chromium-65.0.3325.146/base/optional.h.noncopyable chromium-65.0.3325.146/base/optional.h
--- chromium-65.0.3325.146/base/optional.h.noncopyable 2018-03-13 16:52:15.953729689 -0400
+++ chromium-65.0.3325.146/base/optional.h 2018-03-13 16:53:55.365792522 -0400
@@ -45,6 +45,15 @@ struct OptionalStorageBase {
// When T is not trivially destructible we must call its
// destructor before deallocating its memory.
+ // Note that this hides the (implicitly declared) move constructor, which
+ // would be used for constexpr move constructor in OptionalStorage<T>.
+ // It is needed iff T is trivially move constructible. However, the current
+ // is_trivially_{copy,move}_constructible implementation requires
+ // is_trivially_destructible (which looks a bug, cf:
+ // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51452 and
+ // http://cplusplus.github.io/LWG/lwg-active.html#2116), so it is not
+ // necessary for this case at the moment. Please see also the destructor
+ // comment in "is_trivially_destructible = true" specialization below.
~OptionalStorageBase() {
if (!is_null_)
value_.~T();
@@ -78,9 +87,18 @@ struct OptionalStorageBase<T, true /* tr
: is_null_(false), value_(std::forward<Args>(args)...) {}
// When T is trivially destructible (i.e. its destructor does nothing) there
- // is no need to call it. Explicitly defaulting the destructor means it's not
- // user-provided. Those two together make this destructor trivial.
- ~OptionalStorageBase() = default;
+ // is no need to call it. Implicitly defined destructor is trivial, because
+ // both members (bool and union containing only variants which are trivially
+ // destructible) are trivially destructible.
+ // Explicitly-defaulted destructor is also trivial, but do not use it here,
+ // because it hides the implicit move constructor. It is needed to implement
+ // constexpr move constructor in OptionalStorage iff T is trivially move
+ // constructible. Note that, if T is trivially move constructible, the move
+ // constructor of OptionalStorageBase<T> is also implicitly defined and it is
+ // trivially move constructor. If T is not trivially move constructible,
+ // "not declaring move constructor without destructor declaration" here means
+ // "delete move constructor", which works because any move constructor of
+ // OptionalStorage will not refer to it in that case.
template <class... Args>
void Init(Args&&... args) {