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v8/include/cppgc/internal/name-trait.h

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+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef INCLUDE_CPPGC_INTERNAL_NAME_TRAIT_H_
+#define INCLUDE_CPPGC_INTERNAL_NAME_TRAIT_H_
+
+#include <cstddef>
+#include <cstdint>
+#include <type_traits>
+
+#include "cppgc/name-provider.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+#if CPPGC_SUPPORTS_OBJECT_NAMES && defined(__clang__)
+#define CPPGC_SUPPORTS_COMPILE_TIME_TYPENAME 1
+
+// Provides constexpr c-string storage for a name of fixed |Size| characters.
+// Automatically appends terminating 0 byte.
+template <size_t Size>
+struct NameBuffer {
+  char name[Size + 1]{};
+
+  static constexpr NameBuffer FromCString(const char* str) {
+    NameBuffer result;
+    for (size_t i = 0; i < Size; ++i) result.name[i] = str[i];
+    result.name[Size] = 0;
+    return result;
+  }
+};
+
+template <typename T>
+const char* GetTypename() {
+  static constexpr char kSelfPrefix[] =
+      "const char *cppgc::internal::GetTypename() [T =";
+  static_assert(__builtin_strncmp(__PRETTY_FUNCTION__, kSelfPrefix,
+                                  sizeof(kSelfPrefix) - 1) == 0,
+                "The prefix must match");
+  static constexpr const char* kTypenameStart =
+      __PRETTY_FUNCTION__ + sizeof(kSelfPrefix);
+  static constexpr size_t kTypenameSize =
+      __builtin_strlen(__PRETTY_FUNCTION__) - sizeof(kSelfPrefix) - 1;
+  // NameBuffer is an indirection that is needed to make sure that only a
+  // substring of __PRETTY_FUNCTION__ gets materialized in the binary.
+  static constexpr auto buffer =
+      NameBuffer<kTypenameSize>::FromCString(kTypenameStart);
+  return buffer.name;
+}
+
+#else
+#define CPPGC_SUPPORTS_COMPILE_TIME_TYPENAME 0
+#endif
+
+struct HeapObjectName {
+  const char* value;
+  bool name_was_hidden;
+};
+
+enum class HeapObjectNameForUnnamedObject : uint8_t {
+  kUseClassNameIfSupported,
+  kUseHiddenName,
+};
+
+class V8_EXPORT NameTraitBase {
+ protected:
+  static HeapObjectName GetNameFromTypeSignature(const char*);
+};
+
+// Trait that specifies how the garbage collector retrieves the name for a
+// given object.
+template <typename T>
+class NameTrait final : public NameTraitBase {
+ public:
+  static constexpr bool HasNonHiddenName() {
+#if CPPGC_SUPPORTS_COMPILE_TIME_TYPENAME
+    return true;
+#elif CPPGC_SUPPORTS_OBJECT_NAMES
+    return true;
+#else   // !CPPGC_SUPPORTS_OBJECT_NAMES
+    return std::is_base_of<NameProvider, T>::value;
+#endif  // !CPPGC_SUPPORTS_OBJECT_NAMES
+  }
+
+  static HeapObjectName GetName(
+      const void* obj, HeapObjectNameForUnnamedObject name_retrieval_mode) {
+    return GetNameFor(static_cast<const T*>(obj), name_retrieval_mode);
+  }
+
+ private:
+  static HeapObjectName GetNameFor(const NameProvider* name_provider,
+                                   HeapObjectNameForUnnamedObject) {
+    // Objects inheriting from `NameProvider` are not considered unnamed as
+    // users already provided a name for them.
+    return {name_provider->GetHumanReadableName(), false};
+  }
+
+  static HeapObjectName GetNameFor(
+      const void*, HeapObjectNameForUnnamedObject name_retrieval_mode) {
+    if (name_retrieval_mode == HeapObjectNameForUnnamedObject::kUseHiddenName)
+      return {NameProvider::kHiddenName, true};
+
+#if CPPGC_SUPPORTS_COMPILE_TIME_TYPENAME
+    return {GetTypename<T>(), false};
+#elif CPPGC_SUPPORTS_OBJECT_NAMES
+
+#if defined(V8_CC_GNU)
+#define PRETTY_FUNCTION_VALUE __PRETTY_FUNCTION__
+#elif defined(V8_CC_MSVC)
+#define PRETTY_FUNCTION_VALUE __FUNCSIG__
+#else
+#define PRETTY_FUNCTION_VALUE nullptr
+#endif
+
+    static const HeapObjectName leaky_name =
+        GetNameFromTypeSignature(PRETTY_FUNCTION_VALUE);
+    return leaky_name;
+
+#undef PRETTY_FUNCTION_VALUE
+
+#else   // !CPPGC_SUPPORTS_OBJECT_NAMES
+    return {NameProvider::kHiddenName, true};
+#endif  // !CPPGC_SUPPORTS_OBJECT_NAMES
+  }
+};
+
+using NameCallback = HeapObjectName (*)(const void*,
+                                        HeapObjectNameForUnnamedObject);
+
+}  // namespace internal
+}  // namespace cppgc
+
+#undef CPPGC_SUPPORTS_COMPILE_TIME_TYPENAME
+
+#endif  // INCLUDE_CPPGC_INTERNAL_NAME_TRAIT_H_