Export of internal Abseil changes

--
6b5be2524a088d0f4e8475794dc71232a24e94d8 by Abseil Team <absl-team@google.com>:

Enable ABSL_HAVE_ATTRIBUTE_WEAK for Windows with Clang >= 9.0.0

The bug (https://bugs.llvm.org/show_bug.cgi?id=37598) motivated the workaround
was fixed in 9.0.0.

PiperOrigin-RevId: 365682074

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c16b7784978a370658dce6d82cb7055316a79bcc by Abseil Team <absl-team@google.com>:

Add IsFlat() evaluation to GetFlatAux for RingBuffer

PiperOrigin-RevId: 365666501

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c064eb686a3c036e093e71126c45f97d3a921569 by Abseil Team <absl-team@google.com>:

Implement C++11 compatible std::remove_cvref added in C++20

PiperOrigin-RevId: 365606639

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af2e7e055172da914e63c05308aedb68e197661e by Abseil Team <absl-team@google.com>:

Add IsFlat() support to CordRepRing

PiperOrigin-RevId: 365562090

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2cfeff9280f4967c4f828812bfe153b4e9cbabb7 by Abseil Team <absl-team@google.com>:

Make unit test for TryFlat on 'substring of rep' explicit

PiperOrigin-RevId: 365081382
GitOrigin-RevId: 6b5be2524a088d0f4e8475794dc71232a24e94d8
Change-Id: Ibb577748176217ce237614a6fe77c05375a97003

1 files changed, 31 insertions, 0 deletions

diff --git a/absl/strings/internal/cord_rep_ring.h b/absl/strings/internal/cord_rep_ring.h
index c74d3353..830f2b2a 100644
--- a/absl/strings/internal/cord_rep_ring.h
+++ b/absl/strings/internal/cord_rep_ring.h
@@ -237,6 +237,18 @@ class CordRepRing : public CordRep {
   // Returns the character at `offset`. Requires that `offset < length`.
   char GetCharacter(size_t offset) const;
 
+  // Returns true if this instance manages a single contiguous buffer, in which
+  // case the (optional) output parameter `fragment` is set. Otherwise, the
+  // function returns false, and `fragment` is left unchanged.
+  bool IsFlat(absl::string_view* fragment) const;
+
+  // Returns true if the data starting at `offset` with length `length` is
+  // managed by this instance inside a single contiguous buffer, in which case
+  // the (optional) output parameter `fragment` is set to the contiguous memory
+  // starting at offset `offset` with length `length`. Otherwise, the function
+  // returns false, and `fragment` is left unchanged.
+  bool IsFlat(size_t offset, size_t length, absl::string_view* fragment) const;
+
   // Testing only: set capacity to requested capacity.
   void SetCapacityForTesting(size_t capacity);
 
@@ -576,6 +588,25 @@ inline const CordRepRing* CordRep::ring() const {
   return static_cast<const CordRepRing*>(this);
 }
 
+inline bool CordRepRing::IsFlat(absl::string_view* fragment) const {
+  if (entries() == 1) {
+    if (fragment) *fragment = entry_data(head());
+    return true;
+  }
+  return false;
+}
+
+inline bool CordRepRing::IsFlat(size_t offset, size_t length,
+                                absl::string_view* fragment) const {
+  const Position pos = Find(offset);
+  const absl::string_view data = entry_data(pos.index);
+  if (data.length() >= length && data.length() - length >= pos.offset) {
+    if (fragment) *fragment = data.substr(pos.offset, length);
+    return true;
+  }
+  return false;
+}
+
 std::ostream& operator<<(std::ostream& s, const CordRepRing& rep);
 
 #ifdef __clang__