Export of internal Abseil changes

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5b9d5ce21074c0541432555d383d1b9c5898b553 by Gennadiy Rozental <rogeeff@google.com>:

Convert FlagSaver into public API

PiperOrigin-RevId: 314799739

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5f796c9862b1177f161f4b10fe1a84698ebbb5cf by Abseil Team <absl-team@google.com>:

Google-internal changes only.

PiperOrigin-RevId: 314786474

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67f2ae0ac5ae73bcd9d57a058ac4fea8fc1243ba by Gennadiy Rozental <rogeeff@google.com>:

Makes sure stacktrace_generic is only used with glibc.

Fixes #701

PiperOrigin-RevId: 314726944

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efb1ef3636b0698b79d3ee3590f12c4dff32a3cb by Samuel Benzaquen <sbenza@google.com>:

Take the bits into account when reserving the space for the operation, not just
the exponent.

PiperOrigin-RevId: 314622744
GitOrigin-RevId: 5b9d5ce21074c0541432555d383d1b9c5898b553
Change-Id: I080a5e333e2dc1545b5aa0417882f7ac7116a20c

8 files changed, 50 insertions, 48 deletions

diff --git a/absl/flags/commandlineflag_test.cc b/absl/flags/commandlineflag_test.cc
index cc8eae91..c5afff61 100644
--- a/absl/flags/commandlineflag_test.cc
+++ b/absl/flags/commandlineflag_test.cc
@@ -47,7 +47,7 @@ class CommandLineFlagTest : public testing::Test {
     absl::SetFlagsUsageConfig(default_config);
   }
 
-  void SetUp() override { flag_saver_ = absl::make_unique<flags::FlagSaver>(); }
+  void SetUp() override { flag_saver_ = absl::make_unique<absl::FlagSaver>(); }
   void TearDown() override { flag_saver_.reset(); }
 
  private:
@@ -60,7 +60,7 @@ class CommandLineFlagTest : public testing::Test {
     return std::string(fname);
   }
 
-  std::unique_ptr<flags::FlagSaver> flag_saver_;
+  std::unique_ptr<absl::FlagSaver> flag_saver_;
 };
 
 TEST_F(CommandLineFlagTest, TestAttributesAccessMethods) {
diff --git a/absl/flags/flag_test.cc b/absl/flags/flag_test.cc
index 0c88e24a..2eb2ba71 100644
--- a/absl/flags/flag_test.cc
+++ b/absl/flags/flag_test.cc
@@ -81,7 +81,7 @@ class FlagTest : public testing::Test {
 #endif
     return std::string(fname);
   }
-  flags::FlagSaver flag_saver_;
+  absl::FlagSaver flag_saver_;
 };
 
 struct S1 {
diff --git a/absl/flags/internal/registry.h b/absl/flags/internal/registry.h
index 1e655a3e..c72eebe2 100644
--- a/absl/flags/internal/registry.h
+++ b/absl/flags/internal/registry.h
@@ -89,31 +89,6 @@ inline bool RetiredFlag(const char* flag_name) {
   return flags_internal::Retire(flag_name, base_internal::FastTypeId<T>());
 }
 
-//-----------------------------------------------------------------------------
-// Saves the states (value, default value, whether the user has set
-// the flag, registered validators, etc) of all flags, and restores
-// them when the FlagSaver is destroyed.
-//
-// This class is thread-safe.  However, its destructor writes to
-// exactly the set of flags that have changed value during its
-// lifetime, so concurrent _direct_ access to those flags
-// (i.e. FLAGS_foo instead of {Get,Set}CommandLineOption()) is unsafe.
-
-class FlagSaver {
- public:
-  FlagSaver();
-  ~FlagSaver();
-
-  FlagSaver(const FlagSaver&) = delete;
-  void operator=(const FlagSaver&) = delete;
-
-  // Prevents saver from restoring the saved state of flags.
-  void Ignore();
-
- private:
-  class FlagSaverImpl* impl_;  // we use pimpl here to keep API steady
-};
-
 }  // namespace flags_internal
 ABSL_NAMESPACE_END
 }  // namespace absl
diff --git a/absl/flags/internal/usage_test.cc b/absl/flags/internal/usage_test.cc
index 46f85b55..6e583fbe 100644
--- a/absl/flags/internal/usage_test.cc
+++ b/absl/flags/internal/usage_test.cc
@@ -89,7 +89,7 @@ class UsageReportingTest : public testing::Test {
   }
 
  private:
-  flags::FlagSaver flag_saver_;
+  absl::FlagSaver flag_saver_;
 };
 
 // --------------------------------------------------------------------
diff --git a/absl/flags/parse_test.cc b/absl/flags/parse_test.cc
index 1ab87690..67ae8aad 100644
--- a/absl/flags/parse_test.cc
+++ b/absl/flags/parse_test.cc
@@ -208,7 +208,7 @@ using testing::ElementsAreArray;
 
 class ParseTest : public testing::Test {
  private:
-  flags::FlagSaver flag_saver_;
+  absl::FlagSaver flag_saver_;
 };
 
 // --------------------------------------------------------------------
diff --git a/absl/flags/reflection.cc b/absl/flags/reflection.cc
index 02bb6c2e..5fc945f2 100644
--- a/absl/flags/reflection.cc
+++ b/absl/flags/reflection.cc
@@ -65,7 +65,8 @@ class FlagRegistry {
   static FlagRegistry& GlobalRegistry();  // returns a singleton registry
 
  private:
-  friend class FlagSaverImpl;  // reads all the flags in order to copy them
+  friend class flags_internal::FlagSaverImpl;  // reads all the flags in order
+                                               // to copy them
   friend void ForEachFlagUnlocked(
       std::function<void(CommandLineFlag&)> visitor);
 
@@ -249,15 +250,6 @@ bool Retire(const char* name, FlagFastTypeId type_id) {
 
 // --------------------------------------------------------------------
 
-// FlagSaver
-// FlagSaverImpl
-//    This class stores the states of all flags at construct time,
-//    and restores all flags to that state at destruct time.
-//    Its major implementation challenge is that it never modifies
-//    pointers in the 'main' registry, so global FLAG_* vars always
-//    point to the right place.
-// --------------------------------------------------------------------
-
 class FlagSaverImpl {
  public:
   FlagSaverImpl() = default;
@@ -288,11 +280,10 @@ class FlagSaverImpl {
       backup_registry_;
 };
 
-FlagSaver::FlagSaver() : impl_(new FlagSaverImpl) { impl_->SaveFromRegistry(); }
+}  // namespace flags_internal
 
-void FlagSaver::Ignore() {
-  delete impl_;
-  impl_ = nullptr;
+FlagSaver::FlagSaver() : impl_(new flags_internal::FlagSaverImpl) {
+  impl_->SaveFromRegistry();
 }
 
 FlagSaver::~FlagSaver() {
@@ -304,8 +295,6 @@ FlagSaver::~FlagSaver() {
 
 // --------------------------------------------------------------------
 
-}  // namespace flags_internal
-
 CommandLineFlag* FindCommandLineFlag(absl::string_view name) {
   if (name.empty()) return nullptr;
   flags_internal::FlagRegistry& registry =
diff --git a/absl/flags/reflection.h b/absl/flags/reflection.h
index e8e24f68..045f9784 100644
--- a/absl/flags/reflection.h
+++ b/absl/flags/reflection.h
@@ -31,6 +31,9 @@
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
+namespace flags_internal {
+class FlagSaverImpl;
+}  // namespace flags_internal
 
 // FindCommandLineFlag()
 //
@@ -39,6 +42,41 @@ ABSL_NAMESPACE_BEGIN
 // 'retired' flag is specified.
 CommandLineFlag* FindCommandLineFlag(absl::string_view name);
 
+//------------------------------------------------------------------------------
+// FlagSaver
+//------------------------------------------------------------------------------
+//
+// A FlagSaver object stores the state of flags in the scope where the FlagSaver
+// is defined, allowing modification of those flags within that scope and
+// automatic restoration of the flags to their previous state upon leaving the
+// scope.
+//
+// A FlagSaver can be used within tests to temporarily change the test
+// environment and restore the test case to its previous state.
+//
+// Example:
+//
+//   void MyFunc() {
+//    absl::FlagSaver fs;
+//    ...
+//    absl::SetFlag(FLAGS_myFlag, otherValue);
+//    ...
+//  } // scope of FlagSaver left, flags return to previous state
+//
+// This class is thread-safe.
+
+class FlagSaver {
+ public:
+  FlagSaver();
+  ~FlagSaver();
+
+  FlagSaver(const FlagSaver&) = delete;
+  void operator=(const FlagSaver&) = delete;
+
+ private:
+  flags_internal::FlagSaverImpl* impl_;
+};
+
 //-----------------------------------------------------------------------------
 
 ABSL_NAMESPACE_END
diff --git a/absl/flags/reflection_test.cc b/absl/flags/reflection_test.cc
index 2a137bf7..9781e597 100644
--- a/absl/flags/reflection_test.cc
+++ b/absl/flags/reflection_test.cc
@@ -34,11 +34,11 @@ namespace flags = absl::flags_internal;
 
 class ReflectionTest : public testing::Test {
  protected:
-  void SetUp() override { flag_saver_ = absl::make_unique<flags::FlagSaver>(); }
+  void SetUp() override { flag_saver_ = absl::make_unique<absl::FlagSaver>(); }
   void TearDown() override { flag_saver_.reset(); }
 
  private:
-  std::unique_ptr<flags::FlagSaver> flag_saver_;
+  std::unique_ptr<absl::FlagSaver> flag_saver_;
 };
 
 // --------------------------------------------------------------------