Export of internal Abseil changes

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cfb567ed02096320663d882d2c0c2fb7db7af1e4 by Derek Mauro <dmauro@google.com>:

Upgrade to GCC 10.2.0, Bazel 3.5.0, and CMake 3.18.2

PiperOrigin-RevId: 330847323

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5dcb9ce14d92315163079366a91c43cbd5184ea4 by Evan Brown <ezb@google.com>:

Optimize equal_range() by avoiding the call to upper_bound() when possible.

We need to support heterogeneous comparators that have different behavior when comparing key_type to non-key_type. See the new test.

Also update the comment for `key_compare_to_adapter`.

PiperOrigin-RevId: 330794444

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744405dbda5513527d74094a5c3b9db1e0927693 by Gennadiy Rozental <rogeeff@google.com>:

Introduce trampoline for friend access to avoid friending routines and classes from different namespace.

PiperOrigin-RevId: 330773156

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a195d1226576f8a7bb5671f3e42d1021b827fad9 by Abseil Team <absl-team@google.com>:

Fix an incorrect version number test for std::variant availability in tvOs.

PiperOrigin-RevId: 330759480

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58b02eb9159a577953676d9928cb26b30068b847 by Derek Mauro <dmauro@google.com>:

Use c++20 instead of c++2a now that it is supported by GCC

PiperOrigin-RevId: 330559797
GitOrigin-RevId: cfb567ed02096320663d882d2c0c2fb7db7af1e4
Change-Id: I0e0d68409c95da42f5609920155ba5694ade8df0

2 files changed, 34 insertions, 24 deletions

diff --git a/absl/flags/flag.h b/absl/flags/flag.h
index cdac545b..a9cb2b79 100644
--- a/absl/flags/flag.h
+++ b/absl/flags/flag.h
@@ -144,11 +144,17 @@ class Flag {
   inline bool IsOfType() const {
     return GetImpl().template IsOfType<U>();
   }
-  T Get() const { return GetImpl().Get(); }
-  void Set(const T& v) { GetImpl().Set(v); }
+  T Get() const {
+    return flags_internal::FlagImplPeer::InvokeGet<T>(GetImpl());
+  }
+  void Set(const T& v) {
+    flags_internal::FlagImplPeer::InvokeSet(GetImpl(), v);
+  }
   void InvokeCallback() { GetImpl().InvokeCallback(); }
 
-  const CommandLineFlag& Reflect() const { return GetImpl().Reflect(); }
+  const CommandLineFlag& Reflect() const {
+    return flags_internal::FlagImplPeer::InvokeReflect(GetImpl());
+  }
 
   // The data members are logically private, but they need to be public for
   // this to be an aggregate type.
@@ -180,7 +186,7 @@ class Flag {
 //   std::string first_name = absl::GetFlag(FLAGS_firstname);
 template <typename T>
 ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) {
-  return flag.Get();
+  return flags_internal::FlagImplPeer::InvokeGet<T>(flag);
 }
 
 // SetFlag()
@@ -192,7 +198,7 @@ ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) {
 // but especially within performance-critical code.
 template <typename T>
 void SetFlag(absl::Flag<T>* flag, const T& v) {
-  flag->Set(v);
+  flags_internal::FlagImplPeer::InvokeSet(*flag, v);
 }
 
 // Overload of `SetFlag()` to allow callers to pass in a value that is
@@ -201,7 +207,7 @@ void SetFlag(absl::Flag<T>* flag, const T& v) {
 template <typename T, typename V>
 void SetFlag(absl::Flag<T>* flag, const V& v) {
   T value(v);
-  flag->Set(value);
+  flags_internal::FlagImplPeer::InvokeSet(*flag, value);
 }
 
 // GetFlagReflectionHandle()
@@ -216,7 +222,7 @@ void SetFlag(absl::Flag<T>* flag, const V& v) {
 
 template <typename T>
 const CommandLineFlag& GetFlagReflectionHandle(const absl::Flag<T>& f) {
-  return f.Reflect();
+  return flags_internal::FlagImplPeer::InvokeReflect(f);
 }
 
 ABSL_NAMESPACE_END
diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h
index 89e43ad7..370d8a02 100644
--- a/absl/flags/internal/flag.h
+++ b/absl/flags/internal/flag.h
@@ -632,20 +632,9 @@ class Flag {
   std::string CurrentValue() const { return impl_.CurrentValue(); }
 
  private:
-  template <typename U, bool do_register>
+  template <typename, bool>
   friend class FlagRegistrar;
-
-#if !defined(_MSC_VER) || defined(__clang__)
-  template <typename U>
-  friend U absl::GetFlag(const flags_internal::Flag<U>& flag);
-  template <typename U>
-  friend void absl::SetFlag(flags_internal::Flag<U>* flag, const U& v);
-  template <typename U, typename V>
-  friend void absl::SetFlag(flags_internal::Flag<U>* flag, const V& v);
-#else
-  template <typename U>
-  friend class absl::Flag;
-#endif
+  friend class FlagImplPeer;
 
   T Get() const {
     // See implementation notes in CommandLineFlag::Get().
@@ -668,10 +657,6 @@ class Flag {
     impl_.Write(&v);
   }
 
-  template <typename U>
-  friend const CommandLineFlag& absl::GetFlagReflectionHandle(
-      const absl::Flag<U>& f);
-
   // Access to the reflection.
   const CommandLineFlag& Reflect() const { return impl_; }
 
@@ -684,6 +669,25 @@ class Flag {
 };
 
 ///////////////////////////////////////////////////////////////////////////////
+// Trampoline for friend access
+
+class FlagImplPeer {
+ public:
+  template <typename T, typename FlagType>
+  static T InvokeGet(const FlagType& flag) {
+    return flag.Get();
+  }
+  template <typename FlagType, typename T>
+  static void InvokeSet(FlagType& flag, const T& v) {
+    flag.Set(v);
+  }
+  template <typename FlagType>
+  static const CommandLineFlag& InvokeReflect(const FlagType& f) {
+    return f.Reflect();
+  }
+};
+
+///////////////////////////////////////////////////////////////////////////////
 // Implementation of Flag value specific operations routine.
 template <typename T>
 void* FlagOps(FlagOp op, const void* v1, void* v2, void* v3) {