Squashed 'third_party/abseil_cpp/' changes from 768eb2ca2..ccdbb5941

ccdbb5941 Export of internal Abseil changes
01f5f81f9 Export of internal Abseil changes
2c92bdc7c Export of internal Abseil changes
e7ebf9803 Export of internal Abseil changes
2eba343b5 Export of internal Abseil changes
a8b03d90e Export of internal Abseil changes
1d31b5c36 Export of internal Abseil changes
da3a87690 Export of internal Abseil changes
8faf20461 Exclude empty directories (#697)
2069dc796 Export of internal Abseil changes
4832bf6bf Added a BUILD file in root to expose license. (#695)
af8f994af Export of internal Abseil changes
33caf1097 Export of internal Abseil changes
cf1a02e2d Export of internal Abseil changes

git-subtree-dir: third_party/abseil_cpp
git-subtree-split: ccdbb5941f992fabda7eae3ce72f55efc17c826a

1 files changed, 308 insertions, 0 deletions

diff --git a/absl/flags/reflection.cc b/absl/flags/reflection.cc
new file mode 100644
index 000000000000..5fc945f23767
--- /dev/null
+++ b/absl/flags/reflection.cc
@@ -0,0 +1,308 @@
+//
+//  Copyright 2020 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/flags/reflection.h"
+
+#include <assert.h>
+
+#include <map>
+#include <string>
+
+#include "absl/base/config.h"
+#include "absl/base/thread_annotations.h"
+#include "absl/flags/commandlineflag.h"
+#include "absl/flags/internal/private_handle_accessor.h"
+#include "absl/flags/internal/registry.h"
+#include "absl/flags/usage_config.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/string_view.h"
+#include "absl/synchronization/mutex.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace flags_internal {
+
+// --------------------------------------------------------------------
+// FlagRegistry
+//    A FlagRegistry singleton object holds all flag objects indexed by their
+//    names so that if you know a flag's name, you can access or set it. If the
+//    function is named FooLocked(), you must own the registry lock before
+//    calling the function; otherwise, you should *not* hold the lock, and the
+//    function will acquire it itself if needed.
+// --------------------------------------------------------------------
+
+class FlagRegistry {
+ public:
+  FlagRegistry() = default;
+  ~FlagRegistry() = default;
+
+  // Store a flag in this registry. Takes ownership of *flag.
+  void RegisterFlag(CommandLineFlag& flag);
+
+  void Lock() ABSL_EXCLUSIVE_LOCK_FUNCTION(lock_) { lock_.Lock(); }
+  void Unlock() ABSL_UNLOCK_FUNCTION(lock_) { lock_.Unlock(); }
+
+  // Returns the flag object for the specified name, or nullptr if not found.
+  // Will emit a warning if a 'retired' flag is specified.
+  CommandLineFlag* FindFlagLocked(absl::string_view name);
+
+  // Returns the retired flag object for the specified name, or nullptr if not
+  // found or not retired.  Does not emit a warning.
+  CommandLineFlag* FindRetiredFlagLocked(absl::string_view name);
+
+  static FlagRegistry& GlobalRegistry();  // returns a singleton registry
+
+ private:
+  friend class flags_internal::FlagSaverImpl;  // reads all the flags in order
+                                               // to copy them
+  friend void ForEachFlagUnlocked(
+      std::function<void(CommandLineFlag&)> visitor);
+
+  // The map from name to flag, for FindFlagLocked().
+  using FlagMap = std::map<absl::string_view, CommandLineFlag*>;
+  using FlagIterator = FlagMap::iterator;
+  using FlagConstIterator = FlagMap::const_iterator;
+  FlagMap flags_;
+
+  absl::Mutex lock_;
+
+  // Disallow
+  FlagRegistry(const FlagRegistry&);
+  FlagRegistry& operator=(const FlagRegistry&);
+};
+
+CommandLineFlag* FlagRegistry::FindFlagLocked(absl::string_view name) {
+  FlagConstIterator i = flags_.find(name);
+  if (i == flags_.end()) {
+    return nullptr;
+  }
+
+  if (i->second->IsRetired()) {
+    flags_internal::ReportUsageError(
+        absl::StrCat("Accessing retired flag '", name, "'"), false);
+  }
+
+  return i->second;
+}
+
+CommandLineFlag* FlagRegistry::FindRetiredFlagLocked(absl::string_view name) {
+  FlagConstIterator i = flags_.find(name);
+  if (i == flags_.end() || !i->second->IsRetired()) {
+    return nullptr;
+  }
+
+  return i->second;
+}
+
+namespace {
+
+class FlagRegistryLock {
+ public:
+  explicit FlagRegistryLock(FlagRegistry& fr) : fr_(fr) { fr_.Lock(); }
+  ~FlagRegistryLock() { fr_.Unlock(); }
+
+ private:
+  FlagRegistry& fr_;
+};
+
+void DestroyRetiredFlag(CommandLineFlag& flag);
+
+}  // namespace
+
+void FlagRegistry::RegisterFlag(CommandLineFlag& flag) {
+  FlagRegistryLock registry_lock(*this);
+  std::pair<FlagIterator, bool> ins =
+      flags_.insert(FlagMap::value_type(flag.Name(), &flag));
+  if (ins.second == false) {  // means the name was already in the map
+    CommandLineFlag& old_flag = *ins.first->second;
+    if (flag.IsRetired() != old_flag.IsRetired()) {
+      // All registrations must agree on the 'retired' flag.
+      flags_internal::ReportUsageError(
+          absl::StrCat(
+              "Retired flag '", flag.Name(), "' was defined normally in file '",
+              (flag.IsRetired() ? old_flag.Filename() : flag.Filename()), "'."),
+          true);
+    } else if (flags_internal::PrivateHandleAccessor::TypeId(flag) !=
+               flags_internal::PrivateHandleAccessor::TypeId(old_flag)) {
+      flags_internal::ReportUsageError(
+          absl::StrCat("Flag '", flag.Name(),
+                       "' was defined more than once but with "
+                       "differing types. Defined in files '",
+                       old_flag.Filename(), "' and '", flag.Filename(), "'."),
+          true);
+    } else if (old_flag.IsRetired()) {
+      // Retired flag can just be deleted.
+      DestroyRetiredFlag(flag);
+      return;
+    } else if (old_flag.Filename() != flag.Filename()) {
+      flags_internal::ReportUsageError(
+          absl::StrCat("Flag '", flag.Name(),
+                       "' was defined more than once (in files '",
+                       old_flag.Filename(), "' and '", flag.Filename(), "')."),
+          true);
+    } else {
+      flags_internal::ReportUsageError(
+          absl::StrCat(
+              "Something wrong with flag '", flag.Name(), "' in file '",
+              flag.Filename(), "'. One possibility: file '", flag.Filename(),
+              "' is being linked both statically and dynamically into this "
+              "executable. e.g. some files listed as srcs to a test and also "
+              "listed as srcs of some shared lib deps of the same test."),
+          true);
+    }
+    // All cases above are fatal, except for the retired flags.
+    std::exit(1);
+  }
+}
+
+FlagRegistry& FlagRegistry::GlobalRegistry() {
+  static FlagRegistry* global_registry = new FlagRegistry;
+  return *global_registry;
+}
+
+// --------------------------------------------------------------------
+
+void ForEachFlagUnlocked(std::function<void(CommandLineFlag&)> visitor) {
+  FlagRegistry& registry = FlagRegistry::GlobalRegistry();
+  for (FlagRegistry::FlagConstIterator i = registry.flags_.begin();
+       i != registry.flags_.end(); ++i) {
+    visitor(*i->second);
+  }
+}
+
+void ForEachFlag(std::function<void(CommandLineFlag&)> visitor) {
+  FlagRegistry& registry = FlagRegistry::GlobalRegistry();
+  FlagRegistryLock frl(registry);
+  ForEachFlagUnlocked(visitor);
+}
+
+// --------------------------------------------------------------------
+
+bool RegisterCommandLineFlag(CommandLineFlag& flag) {
+  FlagRegistry::GlobalRegistry().RegisterFlag(flag);
+  return true;
+}
+
+// --------------------------------------------------------------------
+
+namespace {
+
+class RetiredFlagObj final : public CommandLineFlag {
+ public:
+  constexpr RetiredFlagObj(const char* name, FlagFastTypeId type_id)
+      : name_(name), type_id_(type_id) {}
+
+ private:
+  absl::string_view Name() const override { return name_; }
+  std::string Filename() const override { return "RETIRED"; }
+  FlagFastTypeId TypeId() const override { return type_id_; }
+  std::string Help() const override { return ""; }
+  bool IsRetired() const override { return true; }
+  bool IsSpecifiedOnCommandLine() const override { return false; }
+  std::string DefaultValue() const override { return ""; }
+  std::string CurrentValue() const override { return ""; }
+
+  // Any input is valid
+  bool ValidateInputValue(absl::string_view) const override { return true; }
+
+  std::unique_ptr<flags_internal::FlagStateInterface> SaveState() override {
+    return nullptr;
+  }
+
+  bool ParseFrom(absl::string_view, flags_internal::FlagSettingMode,
+                 flags_internal::ValueSource, std::string&) override {
+    return false;
+  }
+
+  void CheckDefaultValueParsingRoundtrip() const override {}
+
+  void Read(void*) const override {}
+
+  // Data members
+  const char* const name_;
+  const FlagFastTypeId type_id_;
+};
+
+void DestroyRetiredFlag(CommandLineFlag& flag) {
+  assert(flag.IsRetired());
+  delete static_cast<RetiredFlagObj*>(&flag);
+}
+
+}  // namespace
+
+bool Retire(const char* name, FlagFastTypeId type_id) {
+  auto* flag = new flags_internal::RetiredFlagObj(name, type_id);
+  FlagRegistry::GlobalRegistry().RegisterFlag(*flag);
+  return true;
+}
+
+// --------------------------------------------------------------------
+
+class FlagSaverImpl {
+ public:
+  FlagSaverImpl() = default;
+  FlagSaverImpl(const FlagSaverImpl&) = delete;
+  void operator=(const FlagSaverImpl&) = delete;
+
+  // Saves the flag states from the flag registry into this object.
+  // It's an error to call this more than once.
+  void SaveFromRegistry() {
+    assert(backup_registry_.empty());  // call only once!
+    flags_internal::ForEachFlag([&](CommandLineFlag& flag) {
+      if (auto flag_state =
+              flags_internal::PrivateHandleAccessor::SaveState(flag)) {
+        backup_registry_.emplace_back(std::move(flag_state));
+      }
+    });
+  }
+
+  // Restores the saved flag states into the flag registry.
+  void RestoreToRegistry() {
+    for (const auto& flag_state : backup_registry_) {
+      flag_state->Restore();
+    }
+  }
+
+ private:
+  std::vector<std::unique_ptr<flags_internal::FlagStateInterface>>
+      backup_registry_;
+};
+
+}  // namespace flags_internal
+
+FlagSaver::FlagSaver() : impl_(new flags_internal::FlagSaverImpl) {
+  impl_->SaveFromRegistry();
+}
+
+FlagSaver::~FlagSaver() {
+  if (!impl_) return;
+
+  impl_->RestoreToRegistry();
+  delete impl_;
+}
+
+// --------------------------------------------------------------------
+
+CommandLineFlag* FindCommandLineFlag(absl::string_view name) {
+  if (name.empty()) return nullptr;
+  flags_internal::FlagRegistry& registry =
+      flags_internal::FlagRegistry::GlobalRegistry();
+  flags_internal::FlagRegistryLock frl(registry);
+
+  return registry.FindFlagLocked(name);
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl