Export of internal Abseil changes

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97faa5fdfa4cd5d7a74cd9332cddd8a7c1e67b89 by Abseil Team <absl-team@google.com>:

Internal changes

PiperOrigin-RevId: 295164378

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74990f100b3f4172c770ef8c76c05c8e99febdde by Xiaoyi Zhang <zhangxy@google.com>:

Release `absl::Cord`.

PiperOrigin-RevId: 295161959

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6018c57f43c45c31dc1a61c0cd75fa2aa9be8dab by Gennadiy Rozental <rogeeff@google.com>:

Introduce independent notion of FlagStaticTypeID.

This change separates static flag value type identification from the type specific "vtable" with all the operations specific to value type. This change allows us to do the following:
* We can move most of "vtable" implementation from handle header, which will become public soon, into implementation details of Abseil Flag.
* We can combine back marshalling ops and general ops into a single vtable routine. They were split previously to facilitate type identification without requiring marshalling routines to be exposed in header.
* We do not need to store two vtable pointers. We can now store only one. The static type id can be deduced on request.

Overall we are saving 24 bytes per flag according to size_tester run.

PiperOrigin-RevId: 295149687

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986b78e9ba571aa85154e70bda4580edd45bb7bf by Abseil Team <absl-team@google.com>:

Update internal comments.

PiperOrigin-RevId: 295030681

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825412b29fd6015027bbc3e5f802706eee0d2837 by Matthew Brown <matthewbr@google.com>:

Change str_format_internal::ConversionChar to an enum (from a struct-wrapped enum).

PiperOrigin-RevId: 294987462

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f9f88d91809d2cc33fc129df70fa93e7a2c35c69 by Derek Mauro <dmauro@google.com>:

Use more precise wording in the question on live-at-head

PiperOrigin-RevId: 294957679
GitOrigin-RevId: 97faa5fdfa4cd5d7a74cd9332cddd8a7c1e67b89
Change-Id: I081e70d148ffac7296d65e2a2f775f643eaf70bf

1 files changed, 97 insertions, 16 deletions

diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h
index b426ccb..1c2f15d 100644
--- a/absl/flags/internal/flag.h
+++ b/absl/flags/internal/flag.h
@@ -43,6 +43,94 @@ template <typename T>
 class Flag;
 
 ///////////////////////////////////////////////////////////////////////////////
+// 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,
+  kStaticTypeId,
+  kParse,
+  kUnparse,
+};
+using FlagOpFn = void* (*)(FlagOp, const void*, void*, void*);
+
+// The per-type function
+template <typename T>
+void* FlagOps(FlagOp op, const void* v1, void* v2, void* v3) {
+  switch (op) {
+    case flags_internal::kDelete:
+      delete static_cast<const T*>(v1);
+      return nullptr;
+    case flags_internal::kClone:
+      return new T(*static_cast<const T*>(v1));
+    case flags_internal::kCopy:
+      *static_cast<T*>(v2) = *static_cast<const T*>(v1);
+      return nullptr;
+    case flags_internal::kCopyConstruct:
+      new (v2) T(*static_cast<const T*>(v1));
+      return nullptr;
+    case flags_internal::kSizeof:
+      return reinterpret_cast<void*>(sizeof(T));
+    case flags_internal::kStaticTypeId:
+      return reinterpret_cast<void*>(&FlagStaticTypeIdGen<T>);
+    case flags_internal::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 flags_internal::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, nullptr);
+}
+inline void* Clone(FlagOpFn op, const void* obj) {
+  return op(flags_internal::kClone, obj, nullptr, nullptr);
+}
+inline void Copy(FlagOpFn op, const void* src, void* dst) {
+  op(flags_internal::kCopy, src, dst, nullptr);
+}
+inline void CopyConstruct(FlagOpFn op, const void* src, void* dst) {
+  op(flags_internal::kCopyConstruct, src, dst, nullptr);
+}
+inline bool Parse(FlagOpFn op, absl::string_view text, void* dst,
+                  std::string* error) {
+  return op(flags_internal::kParse, &text, dst, error) != nullptr;
+}
+inline std::string Unparse(FlagOpFn 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
+  // `flags_internal::FlagOps()`
+  return static_cast<size_t>(reinterpret_cast<intptr_t>(
+      op(flags_internal::kSizeof, nullptr, nullptr, nullptr)));
+}
+inline FlagStaticTypeId StaticTypeId(FlagOpFn op) {
+  return reinterpret_cast<FlagStaticTypeId>(
+      op(flags_internal::kStaticTypeId, nullptr, nullptr, nullptr));
+}
+
+///////////////////////////////////////////////////////////////////////////////
 // Persistent state of the flag data.
 
 template <typename T>
@@ -273,12 +361,10 @@ struct DynValueDeleter {
 class FlagImpl {
  public:
   constexpr FlagImpl(const char* name, const char* filename, FlagOpFn op,
-                     FlagMarshallingOpFn marshalling_op, FlagHelpArg help,
-                     FlagDfltGenFunc default_value_gen)
+                     FlagHelpArg help, FlagDfltGenFunc default_value_gen)
       : name_(name),
         filename_(filename),
         op_(op),
-        marshalling_op_(marshalling_op),
         help_(help.source),
         help_source_kind_(static_cast<uint8_t>(help.kind)),
         def_kind_(static_cast<uint8_t>(FlagDefaultKind::kGenFunc)),
@@ -306,7 +392,7 @@ class FlagImpl {
   template <typename T, typename std::enable_if<
                             !IsAtomicFlagTypeTrait<T>::value, int>::type = 0>
   void Get(T* dst) const {
-    AssertValidType(&flags_internal::FlagOps<T>);
+    AssertValidType(&flags_internal::FlagStaticTypeIdGen<T>);
     Read(dst);
   }
   // Overload for `GetFlag()` for types that support lock-free reads.
@@ -317,7 +403,7 @@ class FlagImpl {
     // slowing down flag value access due to type validation. That's why
     // this validation is hidden behind !NDEBUG
 #ifndef NDEBUG
-    AssertValidType(&flags_internal::FlagOps<T>);
+    AssertValidType(&flags_internal::FlagStaticTypeIdGen<T>);
 #endif
     using U = flags_internal::BestAtomicType<T>;
     typename U::type r = value_.atomics.template load<T>();
@@ -329,7 +415,7 @@ class FlagImpl {
   }
   template <typename T>
   void Set(const T& src) {
-    AssertValidType(&flags_internal::FlagOps<T>);
+    AssertValidType(&flags_internal::FlagStaticTypeIdGen<T>);
     Write(&src);
   }
 
@@ -388,7 +474,7 @@ class FlagImpl {
   // int. To do that we pass the "assumed" type id (which is deduced from type
   // int) as an argument `op`, which is in turn is validated against the type id
   // stored in flag object by flag definition statement.
-  void AssertValidType(const flags_internal::FlagOpFn op) const;
+  void AssertValidType(FlagStaticTypeId type_id) const;
 
   // Immutable flag's state.
 
@@ -396,10 +482,8 @@ class FlagImpl {
   const char* const name_;
   // The file name where ABSL_FLAG resides.
   const char* const filename_;
-  // Type-specific handler.
+  // Type-specific operations "vtable".
   const FlagOpFn op_;
-  // Marshalling ops handler.
-  const FlagMarshallingOpFn marshalling_op_;
   // Help message literal or function to generate it.
   const FlagHelpMsg help_;
   // Indicates if help message was supplied as literal or generator func.
@@ -456,12 +540,9 @@ class FlagImpl {
 template <typename T>
 class Flag final : public flags_internal::CommandLineFlag {
  public:
-  constexpr Flag(const char* name, const char* filename,
-                 const FlagMarshallingOpFn marshalling_op,
-                 const FlagHelpArg help,
+  constexpr Flag(const char* name, const char* filename, const FlagHelpArg help,
                  const FlagDfltGenFunc default_value_gen)
-      : impl_(name, filename, &FlagOps<T>, marshalling_op, help,
-              default_value_gen) {}
+      : impl_(name, filename, &FlagOps<T>, help, default_value_gen) {}
 
   T Get() const {
     // See implementation notes in CommandLineFlag::Get().
@@ -520,7 +601,7 @@ class Flag final : public flags_internal::CommandLineFlag {
   friend class FlagState<T>;
 
   void Read(void* dst) const override { impl_.Read(dst); }
-  FlagOpFn TypeId() const override { return &FlagOps<T>; }
+  FlagStaticTypeId TypeId() const override { return &FlagStaticTypeIdGen<T>; }
 
   // Flag's data
   FlagImpl impl_;