Export of internal Abseil changes.

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1edfe05ddddca43e7650b2d790df7c8498c0e588 by Abseil Team <absl-team@google.com>:

Adding an assert to catch various misuses of std::optional.

PiperOrigin-RevId: 249427865

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45463bbb7e59dfbc584b2f024368a63db98bd7a8 by CJ Johnson <johnsoncj@google.com>:

Migrates internal member function GetAllocator() to GetAllocPtr() and changes the return type to pointer instead of reference to avoid unnecessary copy in DestroyElements(...)

PiperOrigin-RevId: 249319571

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507835be22af85676143ee0c43a80a52bc32094c by Abseil Team <absl-team@google.com>:

Fix -Wstring-conversion in GetEnvVar (Windows implementation).

PiperOrigin-RevId: 249201897
GitOrigin-RevId: 1edfe05ddddca43e7650b2d790df7c8498c0e588
Change-Id: I9300131887ee507cf80d399c724cf87341e4f11a

1 files changed, 3 insertions, 1 deletions

diff --git a/absl/types/optional.h b/absl/types/optional.h
index 1670022dde4e..142dc83a2039 100644
--- a/absl/types/optional.h
+++ b/absl/types/optional.h
@@ -421,7 +421,9 @@ class optional : private optional_internal::optional_data<T>,
   //
   // Accesses the underlying `T` value of an `optional`. If the `optional` is
   // empty, behavior is undefined.
-  constexpr const T& operator*() const & { return reference(); }
+  constexpr const T& operator*() const& {
+    return ABSL_ASSERT(this->engaged_), reference();
+  }
   T& operator*() & {
     assert(this->engaged_);
     return reference();