Changes imported from Abseil "staging" branch:

- 432508bf64998983b3c194d5f164872ce3c2e573 Put visibility tags into absl external build files by Jon Cohen <cohenjon@google.com>
  - 25d59d11e7b833fe632cddb5bf4d76075ae6282b Use ABSL_PREDICT_TRUE instead of *FALSE for the range che... by Jon Cohen <cohenjon@google.com>
  - 8d8a5890a55ddd19aac849748441eeb57c684f10 Better detection for MSVC support on std::optional. by Xiaoyi Zhang <zhangxy@google.com>
  - c1b31e4a97939885c3bbc23ecb093e9619e73ad1 Internal cleanup by Gennadiy Rozental <rogeeff@google.com>
  - 4f56ad20c4eeccc6f5fb21ec6c7191233d34a090 Internal change. by Matt Calabrese <calabrese@google.com>
  - d2a02b52c75c295708170f4d17b7ff442c8d6a97 Fixed a minor typo in the SimpleAtob() function comment. by Abseil Team <absl-team@google.com>
  - 5adbff5c23a45278d06de2ef3a29ea51b0d1269e Internal cleanup by Gennadiy Rozental <rogeeff@google.com>

GitOrigin-RevId: 432508bf64998983b3c194d5f164872ce3c2e573
Change-Id: I32ddd151d3350b96a22e8f1830f19b59374953ad

absl/types/optional_test.cc

@@ -270,8 +270,17 @@ TEST(optionalTest, CopyConstructor) {
     EXPECT_TRUE(absl::is_trivially_copy_constructible<
                 absl::optional<const TrivialCopyable>>::value);
 #endif
+    // When testing with VS 2017 15.3, there seems to be a bug in MSVC
+    // std::optional when T is volatile-qualified. So skipping this test.
+    // Bug report:
+    // https://connect.microsoft.com/VisualStudio/feedback/details/3142534
+#if defined(ABSL_HAVE_STD_OPTIONAL) && defined(_MSC_VER) && _MSC_VER >= 1911
+#define ABSL_MSVC_OPTIONAL_VOLATILE_COPY_BUG 1
+#endif
+#ifndef ABSL_MSVC_OPTIONAL_VOLATILE_COPY_BUG
     EXPECT_FALSE(std::is_copy_constructible<
                  absl::optional<volatile TrivialCopyable>>::value);
+#endif
   }
 }
 

absl/types/span.h

@@ -378,7 +378,7 @@ class Span {
   //
   // Returns a reference to the i'th element of this span.
   constexpr reference at(size_type i) const {
-    return ABSL_PREDICT_FALSE(i < size())
+    return ABSL_PREDICT_TRUE(i < size())
                ? ptr_[i]
                : (base_internal::ThrowStdOutOfRange(
                       "Span::at failed bounds check"),