Creation of LTS branch "lts_2020_02_25"20200225

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  - ecc0033b54847f6c9ee37dbb0be8aa17e5b6d37b Always enable proper symbolize implementation on Windows ... by Loo Rong Jie <loorongjie@gmail.com>
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  - e9f9000c7c80993cb589d011616b7a8016e42f4a Fix ABSL_WAITER_MODE detection for mingw (#342) by Joe Sylve <Joe.Sylve@gmail.com>
  - abea769b551f7a100f540967cb95debdb0080df8 Fix ABSL_HAVE_ALARM check on mingw (#341) by Joe Sylve <Joe.Sylve@gmail.com>
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  - 0302d1e5fa4fcdd1763b7d1bb3212943b1ae911d supppress unused variable warning for gcc (#372) by Martin <pizzard@users.noreply.github.com>
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  - 36910d3d7e9fccadd6603f232d0c4f54dcd47c7e [bazel] Add fixes for --incompatible_load_cc_rules_from_b... by Yannic <contact@yannic-bonenberger.com>
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GitOrigin-RevId: 0033c9ea91a52ade7c6b725aa2ef3cbe15463421
Change-Id: I8a2b70063cb3ab40c6943a6db0fe40cae71ed8d7

1 files changed, 121 insertions, 293 deletions

diff --git a/absl/flags/internal/commandlineflag.h b/absl/flags/internal/commandlineflag.h
index 382553d2..6363c661 100644
--- a/absl/flags/internal/commandlineflag.h
+++ b/absl/flags/internal/commandlineflag.h
@@ -16,30 +16,41 @@
 #ifndef ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_
 #define ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_
 
-#include <atomic>
+#include <stddef.h>
+#include <stdint.h>
 
+#include <memory>
+#include <string>
+#include <typeinfo>
+
+#include "absl/base/config.h"
 #include "absl/base/macros.h"
+#include "absl/flags/config.h"
 #include "absl/flags/marshalling.h"
-#include "absl/synchronization/mutex.h"
+#include "absl/strings/string_view.h"
 #include "absl/types/optional.h"
 
 namespace absl {
-inline namespace lts_2019_08_08 {
+ABSL_NAMESPACE_BEGIN
 namespace flags_internal {
 
-// Type-specific operations, eg., parsing, copying, etc. are provided
-// by function specific to that type with a signature matching FlagOpFn.
-enum FlagOp {
-  kDelete,
-  kClone,
-  kCopy,
-  kCopyConstruct,
-  kSizeof,
-  kParse,
-  kUnparse
-};
-using FlagOpFn = void* (*)(FlagOp, const void*, void*);
-using FlagMarshallingOpFn = void* (*)(FlagOp, const void*, void*, void*);
+// An alias for flag static type id. Values of type identify the flag value type
+// simialarly to typeid(T), but without relying on RTTI being available. In most
+// cases this id is enough to uniquely identify the flag's value type. In a few
+// cases we'll have to resort to using actual RTTI implementation if it is
+// available.
+using FlagStaticTypeId = void* (*)();
+
+// Address of this function template is used in current implementation as a flag
+// static type id.
+template <typename T>
+void* FlagStaticTypeIdGen() {
+#if defined(ABSL_FLAGS_INTERNAL_HAS_RTTI)
+  return const_cast<std::type_info*>(&typeid(T));
+#else
+  return nullptr;
+#endif
+}
 
 // Options that control SetCommandLineOptionWithMode.
 enum FlagSettingMode {
@@ -62,215 +73,95 @@ enum ValueSource {
   kProgrammaticChange,
 };
 
-// Signature for the help generation function used as an argument for the
-// absl::Flag constructor.
-using HelpGenFunc = std::string (*)();
-
-// Signature for the function generating the initial flag value based (usually
-// based on default value supplied in flag's definition)
-using InitialValGenFunc = void* (*)();
-
-struct CommandLineFlagInfo;
-
-// Signature for the mutation callback used by watched Flags
-// The callback is noexcept.
-// TODO(rogeeff): add noexcept after C++17 support is added.
-using FlagCallback = void (*)();
-
-using FlagValidator = bool (*)();
-
-extern const char kStrippedFlagHelp[];
-
-// The per-type function
-template <typename T>
-void* FlagOps(FlagOp op, const void* v1, void* v2) {
-  switch (op) {
-    case kDelete:
-      delete static_cast<const T*>(v1);
-      return nullptr;
-    case kClone:
-      return new T(*static_cast<const T*>(v1));
-    case kCopy:
-      *static_cast<T*>(v2) = *static_cast<const T*>(v1);
-      return nullptr;
-    case kCopyConstruct:
-      new (v2) T(*static_cast<const T*>(v1));
-      return nullptr;
-    case kSizeof:
-      return reinterpret_cast<void*>(sizeof(T));
-    default:
-      return nullptr;
-  }
-}
-
-template <typename T>
-void* FlagMarshallingOps(FlagOp op, const void* v1, void* v2, void* v3) {
-  switch (op) {
-    case kParse: {
-      // initialize the temporary instance of type T based on current value in
-      // destination (which is going to be flag's default value).
-      T temp(*static_cast<T*>(v2));
-      if (!absl::ParseFlag<T>(*static_cast<const absl::string_view*>(v1), &temp,
-                              static_cast<std::string*>(v3))) {
-        return nullptr;
-      }
-      *static_cast<T*>(v2) = std::move(temp);
-      return v2;
-    }
-    case kUnparse:
-      *static_cast<std::string*>(v2) =
-          absl::UnparseFlag<T>(*static_cast<const T*>(v1));
-      return nullptr;
-    default:
-      return nullptr;
-  }
-}
-
-// Functions that invoke flag-type-specific operations.
-inline void Delete(FlagOpFn op, const void* obj) {
-  op(flags_internal::kDelete, obj, nullptr);
-}
-
-inline void* Clone(FlagOpFn op, const void* obj) {
-  return op(flags_internal::kClone, obj, nullptr);
-}
-
-inline void Copy(FlagOpFn op, const void* src, void* dst) {
-  op(flags_internal::kCopy, src, dst);
-}
-
-inline void CopyConstruct(FlagOpFn op, const void* src, void* dst) {
-  op(flags_internal::kCopyConstruct, src, dst);
-}
-
-inline bool Parse(FlagMarshallingOpFn op, absl::string_view text, void* dst,
-                  std::string* error) {
-  return op(flags_internal::kParse, &text, dst, error) != nullptr;
-}
-
-inline std::string Unparse(FlagMarshallingOpFn op, const void* val) {
-  std::string result;
-  op(flags_internal::kUnparse, val, &result, nullptr);
-  return result;
-}
-
-inline size_t Sizeof(FlagOpFn op) {
-  // This sequence of casts reverses the sequence from base::internal::FlagOps()
-  return static_cast<size_t>(reinterpret_cast<intptr_t>(
-      op(flags_internal::kSizeof, nullptr, nullptr)));
-}
-
-// The following struct contains the locks in a CommandLineFlag struct.
-// They are in a separate struct that is lazily allocated to avoid problems
-// with static initialization and to avoid multiple allocations.
-struct CommandLineFlagLocks {
-  absl::Mutex primary_mu;   // protects several fields in CommandLineFlag
-  absl::Mutex callback_mu;  // used to serialize callbacks
-};
-
-// Holds either a pointer to help text or a function which produces it.  This is
-// needed for supporting both static initialization of Flags while supporting
-// the legacy registration framework.  We can't use absl::variant<const char*,
-// const char*(*)()> since anybody passing 0 or nullptr in to a CommandLineFlag
-// would find an ambiguity.
-class HelpText {
+// Handle to FlagState objects. Specific flag state objects will restore state
+// of a flag produced this flag state from method CommandLineFlag::SaveState().
+class FlagStateInterface {
  public:
-  static constexpr HelpText FromFunctionPointer(const HelpGenFunc fn) {
-    return HelpText(fn, nullptr);
-  }
-  static constexpr HelpText FromStaticCString(const char* msg) {
-    return HelpText(nullptr, msg);
-  }
-
-  std::string GetHelpText() const;
-
-  HelpText() = delete;
-  HelpText(const HelpText&) = default;
-  HelpText(HelpText&&) = default;
+  virtual ~FlagStateInterface() {}
 
- private:
-  explicit constexpr HelpText(const HelpGenFunc fn, const char* msg)
-      : help_function_(fn), help_message_(msg) {}
-
-  HelpGenFunc help_function_;
-  const char* help_message_;
+  // Restores the flag originated this object to the saved state.
+  virtual void Restore() const = 0;
 };
 
 // Holds all information for a flag.
-struct CommandLineFlag {
-  constexpr CommandLineFlag(
-      const char* name_arg, HelpText help_text, const char* filename_arg,
-      const flags_internal::FlagOpFn op_arg,
-      const flags_internal::FlagMarshallingOpFn marshalling_op_arg,
-      const flags_internal::InitialValGenFunc initial_value_gen,
-      const bool retired_arg, void* def_arg, void* cur_arg)
-      : name(name_arg),
-        help(help_text),
-        filename(filename_arg),
-        op(op_arg),
-        marshalling_op(marshalling_op_arg),
-        make_init_value(initial_value_gen),
-        retired(retired_arg),
-        inited(false),
-        modified(false),
-        on_command_line(false),
-        validator(nullptr),
-        callback(nullptr),
-        def(def_arg),
-        cur(cur_arg),
-        counter(0),
-        atomic(kAtomicInit),
-        locks(nullptr) {}
-
-  // Revert the init routine.
-  void Destroy() const;
+class CommandLineFlag {
+ public:
+  constexpr CommandLineFlag() = default;
 
   // Not copyable/assignable.
   CommandLineFlag(const CommandLineFlag&) = delete;
   CommandLineFlag& operator=(const CommandLineFlag&) = delete;
 
-  absl::string_view Name() const { return name; }
-  std::string Help() const { return help.GetHelpText(); }
-  bool IsRetired() const { return this->retired; }
-  bool IsModified() const;
-  void SetModified(bool is_modified);
-  bool IsSpecifiedOnCommandLine() const;
-  // Returns true iff this is a handle to an Abseil Flag.
-  bool IsAbseilFlag() const {
-    // Set to null for V1 flags
-    return this->make_init_value != nullptr;
-  }
-
-  absl::string_view Typename() const;
-  std::string Filename() const;
-  std::string DefaultValue() const;
-  std::string CurrentValue() const;
-
-  bool HasValidatorFn() const;
-  bool SetValidatorFn(FlagValidator fn);
-  bool InvokeValidator(const void* value) const;
+  // Non-polymorphic access methods.
 
   // Return true iff flag has type T.
   template <typename T>
   inline bool IsOfType() const {
-    return this->op == &flags_internal::FlagOps<T>;
+    return TypeId() == &flags_internal::FlagStaticTypeIdGen<T>;
   }
 
   // Attempts to retrieve the flag value. Returns value on success,
   // absl::nullopt otherwise.
   template <typename T>
   absl::optional<T> Get() const {
-    if (IsRetired() || flags_internal::FlagOps<T> != this->op)
+    if (IsRetired() || !IsOfType<T>()) {
       return absl::nullopt;
+    }
 
-    T res;
-    Read(&res, flags_internal::FlagOps<T>);
-
-    return res;
+    // Implementation notes:
+    //
+    // We are wrapping a union around the value of `T` to serve three purposes:
+    //
+    //  1. `U.value` has correct size and alignment for a value of type `T`
+    //  2. The `U.value` constructor is not invoked since U's constructor does
+    //     not do it explicitly.
+    //  3. The `U.value` destructor is invoked since U's destructor does it
+    //     explicitly. This makes `U` a kind of RAII wrapper around non default
+    //     constructible value of T, which is destructed when we leave the
+    //     scope. We do need to destroy U.value, which is constructed by
+    //     CommandLineFlag::Read even though we left it in a moved-from state
+    //     after std::move.
+    //
+    // All of this serves to avoid requiring `T` being default constructible.
+    union U {
+      T value;
+      U() {}
+      ~U() { value.~T(); }
+    };
+    U u;
+
+    Read(&u.value);
+    return std::move(u.value);
   }
 
-  void SetCallback(const flags_internal::FlagCallback mutation_callback);
-  void InvokeCallback();
+  // Polymorphic access methods
+
+  // Returns name of this flag.
+  virtual absl::string_view Name() const = 0;
+  // Returns name of the file where this flag is defined.
+  virtual std::string Filename() const = 0;
+  // Returns name of the flag's value type for some built-in types or empty
+  // std::string.
+  virtual absl::string_view Typename() const = 0;
+  // Returns help message associated with this flag.
+  virtual std::string Help() const = 0;
+  // Returns true iff this object corresponds to retired flag.
+  virtual bool IsRetired() const { return false; }
+  // Returns true iff this is a handle to an Abseil Flag.
+  virtual bool IsAbseilFlag() const { return true; }
+  // Returns id of the flag's value type.
+  virtual FlagStaticTypeId TypeId() const = 0;
+  virtual bool IsModified() const = 0;
+  virtual bool IsSpecifiedOnCommandLine() const = 0;
+  virtual std::string DefaultValue() const = 0;
+  virtual std::string CurrentValue() const = 0;
+
+  // Interfaces to operate on validators.
+  virtual bool ValidateInputValue(absl::string_view value) const = 0;
+
+  // Interface to save flag to some persistent state. Returns current flag state
+  // or nullptr if flag does not support saving and restoring a state.
+  virtual std::unique_ptr<FlagStateInterface> SaveState() = 0;
 
   // Sets the value of the flag based on specified std::string `value`. If the flag
   // was successfully set to new value, it returns true. Otherwise, sets `error`
@@ -280,106 +171,43 @@ struct CommandLineFlag {
   //  * Update the flag's default value
   //  * Update the current flag value if it was never set before
   // The mode is selected based on `set_mode` parameter.
-  bool SetFromString(absl::string_view value,
-                     flags_internal::FlagSettingMode set_mode,
-                     flags_internal::ValueSource source, std::string* error);
-
-  void StoreAtomic(size_t size);
+  virtual bool SetFromString(absl::string_view value,
+                             flags_internal::FlagSettingMode set_mode,
+                             flags_internal::ValueSource source,
+                             std::string* error) = 0;
 
-  void CheckDefaultValueParsingRoundtrip() const;
-  // Invoke the flag validators for old flags.
-  // TODO(rogeeff): implement proper validators for Abseil Flags
-  bool ValidateDefaultValue() const;
-  bool ValidateInputValue(absl::string_view value) const;
-
-  // Constant configuration for a particular flag.
- private:
-  const char* const name;
-  const HelpText help;
-  const char* const filename;
+  // Checks that flags default value can be converted to std::string and back to the
+  // flag's value type.
+  virtual void CheckDefaultValueParsingRoundtrip() const = 0;
 
  protected:
-  const FlagOpFn op;                         // Type-specific handler
-  const FlagMarshallingOpFn marshalling_op;  // Marshalling ops handler
-  const InitialValGenFunc make_init_value;   // Makes initial value for the flag
-  const bool retired;                        // Is the flag retired?
-  std::atomic<bool> inited;  // fields have been lazily initialized
+  ~CommandLineFlag() = default;
 
-  // Mutable state (guarded by locks->primary_mu).
-  bool modified;            // Has flag value been modified?
-  bool on_command_line;     // Specified on command line.
-  FlagValidator validator;  // Validator function, or nullptr
-  FlagCallback callback;    // Mutation callback, or nullptr
-  void* def;                // Lazily initialized pointer to default value
-  void* cur;                // Lazily initialized pointer to current value
-  int64_t counter;            // Mutation counter
-
-  // For some types, a copy of the current value is kept in an atomically
-  // accessible field.
-  static const int64_t kAtomicInit = 0xababababababababll;
-  std::atomic<int64_t> atomic;
-
-  // Lazily initialized mutexes for this flag value.  We cannot inline a
-  // SpinLock or Mutex here because those have non-constexpr constructors and
-  // so would prevent constant initialization of this type.
-  // TODO(rogeeff): fix it once Mutex has constexpr constructor
-  struct CommandLineFlagLocks* locks;  // locks, laziliy allocated.
-
-  // Ensure that the lazily initialized fields of *flag have been initialized,
-  // and return the lock which should be locked when flag's state is mutated.
-  absl::Mutex* InitFlagIfNecessary() const;
-
-  // copy construct new value of flag's type in a memory referenced by dst
-  // based on current flag's value
-  void Read(void* dst, const flags_internal::FlagOpFn dst_op) const;
-  // updates flag's value to *src (locked)
-  void Write(const void* src, const flags_internal::FlagOpFn src_op);
-
-  friend class FlagRegistry;
-  friend class FlagPtrMap;
-  friend class FlagSaverImpl;
-  friend void FillCommandLineFlagInfo(CommandLineFlag* flag,
-                                      CommandLineFlagInfo* result);
-  friend bool TryParseLocked(CommandLineFlag* flag, void* dst,
-                             absl::string_view value, std::string* err);
-  friend absl::Mutex* InitFlag(CommandLineFlag* flag);
+ private:
+  // Copy-construct a new value of the flag's type in a memory referenced by
+  // the dst based on the current flag's value.
+  virtual void Read(void* dst) const = 0;
 };
 
-// Update any copy of the flag value that is stored in an atomic word.
-// In addition if flag has a mutation callback this function invokes it. While
-// callback is being invoked the primary flag's mutex is unlocked and it is
-// re-locked back after call to callback is completed. Callback invocation is
-// guarded by flag's secondary mutex instead which prevents concurrent callback
-// invocation. Note that it is possible for other thread to grab the primary
-// lock and update flag's value at any time during the callback invocation.
-// This is by design. Callback can get a value of the flag if necessary, but it
-// might be different from the value initiated the callback and it also can be
-// different by the time the callback invocation is completed.
-// Requires that *primary_lock be held in exclusive mode; it may be released
-// and reacquired by the implementation.
-void UpdateCopy(CommandLineFlag* flag);
-// Return true iff flag value was changed via direct-access.
-bool ChangedDirectly(CommandLineFlag* flag, const void* a, const void* b);
-
-// This macro is the "source of truth" for the list of supported flag types we
-// expect to perform lock free operations on. Specifically it generates code,
-// a one argument macro operating on a type, supplied as a macro argument, for
-// each type in the list.
-#define ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(A) \
-  A(bool)                                         \
-  A(short)                                        \
-  A(unsigned short)                               \
-  A(int)                                          \
-  A(unsigned int)                                 \
-  A(long)                                         \
-  A(unsigned long)                                \
-  A(long long)                                    \
-  A(unsigned long long)                           \
-  A(double)                                       \
-  A(float)
+// This macro is the "source of truth" for the list of supported flag built-in
+// types.
+#define ABSL_FLAGS_INTERNAL_BUILTIN_TYPES(A) \
+  A(bool)                                    \
+  A(short)                                   \
+  A(unsigned short)                          \
+  A(int)                                     \
+  A(unsigned int)                            \
+  A(long)                                    \
+  A(unsigned long)                           \
+  A(long long)                               \
+  A(unsigned long long)                      \
+  A(double)                                  \
+  A(float)                                   \
+  A(std::string)                             \
+  A(std::vector<std::string>)
 
 }  // namespace flags_internal
-}  // inline namespace lts_2019_08_08
+ABSL_NAMESPACE_END
 }  // namespace absl
 
 #endif  // ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_