Fix C++23 compilation errors in leveldb

leveldb Team · pwnall · commit 302786e211d1 · 2025-01-24T21:05:25.000Z
Remove usages of std::aligned_storage, which is deprecated. More details about the replacement in https://crbug.com/388068052. PiperOrigin-RevId: 713346733
diff --git a/include/leveldb/slice.h b/include/leveldb/slice.h
@@ -51,9 +51,6 @@ class LEVELDB_EXPORT Slice {
   // Return true iff the length of the referenced data is zero
   bool empty() const { return size_ == 0; }
 
-  const char* begin() const { return data(); }
-  const char* end() const { return data() + size(); }
-
   // Return the ith byte in the referenced data.
   // REQUIRES: n < size()
   char operator[](size_t n) const {
diff --git a/util/env_posix.cc b/util/env_posix.cc
@@ -874,7 +874,11 @@ class SingletonEnv {
 #endif  // !defined(NDEBUG)
     static_assert(sizeof(env_storage_) >= sizeof(EnvType),
                   "env_storage_ will not fit the Env");
-    static_assert(alignof(decltype(env_storage_)) >= alignof(EnvType),
+    static_assert(std::is_standard_layout_v<SingletonEnv<EnvType>>);
+    static_assert(
+        offsetof(SingletonEnv<EnvType>, env_storage_) % alignof(EnvType) == 0,
+        "env_storage_ does not meet the Env's alignment needs");
+    static_assert(alignof(SingletonEnv<EnvType>) % alignof(EnvType) == 0,
                   "env_storage_ does not meet the Env's alignment needs");
     new (&env_storage_) EnvType();
   }
@@ -892,8 +896,7 @@ class SingletonEnv {
   }
 
  private:
-  typename std::aligned_storage<sizeof(EnvType), alignof(EnvType)>::type
-      env_storage_;
+  alignas(EnvType) char env_storage_[sizeof(EnvType)];
 #if !defined(NDEBUG)
   static std::atomic<bool> env_initialized_;
 #endif  // !defined(NDEBUG)
diff --git a/util/env_windows.cc b/util/env_windows.cc
@@ -769,7 +769,11 @@ class SingletonEnv {
 #endif  // !defined(NDEBUG)
     static_assert(sizeof(env_storage_) >= sizeof(EnvType),
                   "env_storage_ will not fit the Env");
-    static_assert(alignof(decltype(env_storage_)) >= alignof(EnvType),
+    static_assert(std::is_standard_layout_v<SingletonEnv<EnvType>>);
+    static_assert(
+        offsetof(SingletonEnv<EnvType>, env_storage_) % alignof(EnvType) == 0,
+        "env_storage_ does not meet the Env's alignment needs");
+    static_assert(alignof(SingletonEnv<EnvType>) % alignof(EnvType) == 0,
                   "env_storage_ does not meet the Env's alignment needs");
     new (&env_storage_) EnvType();
   }
@@ -787,8 +791,7 @@ class SingletonEnv {
   }
 
  private:
-  typename std::aligned_storage<sizeof(EnvType), alignof(EnvType)>::type
-      env_storage_;
+  alignas(EnvType) char env_storage_[sizeof(EnvType)];
 #if !defined(NDEBUG)
   static std::atomic<bool> env_initialized_;
 #endif  // !defined(NDEBUG)
diff --git a/util/hash.cc b/util/hash.cc
@@ -27,7 +27,7 @@ uint32_t Hash(const char* data, size_t n, uint32_t seed) {
   uint32_t h = seed ^ (n * m);
 
   // Pick up four bytes at a time
-  while (limit - data >= 4) {
+  while (data + 4 <= limit) {
     uint32_t w = DecodeFixed32(data);
     data += 4;
     h += w;
diff --git a/util/no_destructor.h b/util/no_destructor.h
@@ -5,6 +5,7 @@
 #ifndef STORAGE_LEVELDB_UTIL_NO_DESTRUCTOR_H_
 #define STORAGE_LEVELDB_UTIL_NO_DESTRUCTOR_H_
 
+#include <cstddef>
 #include <type_traits>
 #include <utility>
 
@@ -20,8 +21,12 @@ class NoDestructor {
   explicit NoDestructor(ConstructorArgTypes&&... constructor_args) {
     static_assert(sizeof(instance_storage_) >= sizeof(InstanceType),
                   "instance_storage_ is not large enough to hold the instance");
+    static_assert(std::is_standard_layout_v<NoDestructor<InstanceType>>);
     static_assert(
-        alignof(decltype(instance_storage_)) >= alignof(InstanceType),
+        offsetof(NoDestructor, instance_storage_) % alignof(InstanceType) == 0,
+        "instance_storage_ does not meet the instance's alignment requirement");
+    static_assert(
+        alignof(NoDestructor<InstanceType>) % alignof(InstanceType) == 0,
         "instance_storage_ does not meet the instance's alignment requirement");
     new (&instance_storage_)
         InstanceType(std::forward<ConstructorArgTypes>(constructor_args)...);
@@ -37,8 +42,7 @@ class NoDestructor {
   }
 
  private:
-  typename std::aligned_storage<sizeof(InstanceType),
-                                alignof(InstanceType)>::type instance_storage_;
+  alignas(InstanceType) char instance_storage_[sizeof(InstanceType)];
 };
 
 }  // namespace leveldb
