Export of internal Abseil changes.

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fcf9d3facb12451964ad1850073cbfb6f9739379 by CJ Johnson <johnsoncj@google.com>:

Makes it obvious to readers that the comparison operators do not branch more than needed

PiperOrigin-RevId: 240811527

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680c586f81f805be68e96caffb28d5f46b6a6511 by Jon Cohen <cohenjon@google.com>:

Consistently use "if(" instead of "if (" in CMake files

PiperOrigin-RevId: 240621819

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c4acc506648622389f33f564fd94f8dda08cb61a by Tom Manshreck <shreck@google.com>:

Internal change

PiperOrigin-RevId: 240619556

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ddbc1894944aae96767c876a1ae8696ddaba42a2 by Jon Cohen <cohenjon@google.com>:

Remove the warning about install prefixes when we aren't installing abseil

PiperOrigin-RevId: 240614750

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086c4fad213d99e875038bc8a1c7268e28a7ebf3 by Abseil Team <absl-team@google.com>:

Adjust some tests and test cases which fail on WebAssembly

PiperOrigin-RevId: 240592367

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46c2c09723a37ef4911ae3c64aab92e3f0fdba79 by Abseil Team <absl-team@google.com>:

CMake install target update
- Add prefix absl_ to each target when install rule are disabled.
- Disable all install commands when absl is used as subdirectory (Fix #287)

PiperOrigin-RevId: 240575083

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8d88063ed5b16f982a91950693d37ca18fdd46d8 by Jon Cohen <cohenjon@google.com>:

Correctly link to Threads::Threads for a few cmake targets which were missing it.

PiperOrigin-RevId: 240574513
GitOrigin-RevId: fcf9d3facb12451964ad1850073cbfb6f9739379
Change-Id: I031c57de8cd88554348eb8bd1371d01d15ff1fc7

absl/types/span.h

@@ -60,114 +60,18 @@
 #include <cstddef>
 #include <initializer_list>
 #include <iterator>
-#include <string>
 #include <type_traits>
 #include <utility>
 
-#include "absl/algorithm/algorithm.h"
 #include "absl/base/internal/throw_delegate.h"
 #include "absl/base/macros.h"
 #include "absl/base/optimization.h"
-#include "absl/base/port.h"
+#include "absl/base/port.h"    // TODO(strel): remove this include
 #include "absl/meta/type_traits.h"
+#include "absl/types/internal/span.h"
 
 namespace absl {
 
-namespace span_internal {
-// A constexpr min function
-constexpr size_t Min(size_t a, size_t b) noexcept { return a < b ? a : b; }
-
-// Wrappers for access to container data pointers.
-template <typename C>
-constexpr auto GetDataImpl(C& c, char) noexcept  // NOLINT(runtime/references)
-    -> decltype(c.data()) {
-  return c.data();
-}
-
-// Before C++17, std::string::data returns a const char* in all cases.
-inline char* GetDataImpl(std::string& s,  // NOLINT(runtime/references)
-                         int) noexcept {
-  return &s[0];
-}
-
-template <typename C>
-constexpr auto GetData(C& c) noexcept  // NOLINT(runtime/references)
-    -> decltype(GetDataImpl(c, 0)) {
-  return GetDataImpl(c, 0);
-}
-
-// Detection idioms for size() and data().
-template <typename C>
-using HasSize =
-    std::is_integral<absl::decay_t<decltype(std::declval<C&>().size())>>;
-
-// We want to enable conversion from vector<T*> to Span<const T* const> but
-// disable conversion from vector<Derived> to Span<Base>. Here we use
-// the fact that U** is convertible to Q* const* if and only if Q is the same
-// type or a more cv-qualified version of U.  We also decay the result type of
-// data() to avoid problems with classes which have a member function data()
-// which returns a reference.
-template <typename T, typename C>
-using HasData =
-    std::is_convertible<absl::decay_t<decltype(GetData(std::declval<C&>()))>*,
-                        T* const*>;
-
-// Extracts value type from a Container
-template <typename C>
-struct ElementType {
-  using type = typename absl::remove_reference_t<C>::value_type;
-};
-
-template <typename T, size_t N>
-struct ElementType<T (&)[N]> {
-  using type = T;
-};
-
-template <typename C>
-using ElementT = typename ElementType<C>::type;
-
-template <typename T>
-using EnableIfMutable =
-    typename std::enable_if<!std::is_const<T>::value, int>::type;
-
-template <template <typename> class SpanT, typename T>
-bool EqualImpl(SpanT<T> a, SpanT<T> b) {
-  static_assert(std::is_const<T>::value, "");
-  return absl::equal(a.begin(), a.end(), b.begin(), b.end());
-}
-
-template <template <typename> class SpanT, typename T>
-bool LessThanImpl(SpanT<T> a, SpanT<T> b) {
-  // We can't use value_type since that is remove_cv_t<T>, so we go the long way
-  // around.
-  static_assert(std::is_const<T>::value, "");
-  return std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end());
-}
-
-// The `IsConvertible` classes here are needed because of the
-// `std::is_convertible` bug in libcxx when compiled with GCC. This build
-// configuration is used by Android NDK toolchain. Reference link:
-// https://bugs.llvm.org/show_bug.cgi?id=27538.
-template <typename From, typename To>
-struct IsConvertibleHelper {
- private:
-  static std::true_type testval(To);
-  static std::false_type testval(...);
-
- public:
-  using type = decltype(testval(std::declval<From>()));
-};
-
-template <typename From, typename To>
-struct IsConvertible : IsConvertibleHelper<From, To>::type {};
-
-// TODO(zhangxy): replace `IsConvertible` with `std::is_convertible` once the
-// older version of libcxx is not supported.
-template <typename From, typename To>
-using EnableIfConvertibleTo =
-    typename std::enable_if<IsConvertible<From, To>::value>::type;
-}  // namespace span_internal
-
 //------------------------------------------------------------------------------
 // Span
 //------------------------------------------------------------------------------