Add unsigned to character buffers to ensure they can provide storage (https://eel.is/c++draft/intro.object#3)

absl/cleanup/internal/cleanup.h

@@ -88,7 +88,7 @@ class Storage {
 
  private:
   bool is_callback_engaged_;
-  alignas(Callback) char callback_buffer_[sizeof(Callback)];
+  alignas(Callback) unsigned char callback_buffer_[sizeof(Callback)];
 };
 
 }  // namespace cleanup_internal

absl/container/fixed_array.h

@@ -447,7 +447,8 @@ class ABSL_ATTRIBUTE_WARN_UNUSED FixedArray {
 
    private:
     ABSL_ADDRESS_SANITIZER_REDZONE(redzone_begin_);
-    alignas(StorageElement) char buff_[sizeof(StorageElement[inline_elements])];
+    alignas(StorageElement) unsigned char buff_[sizeof(
+        StorageElement[inline_elements])];
     ABSL_ADDRESS_SANITIZER_REDZONE(redzone_end_);
   };
 

absl/container/internal/inlined_vector.h

@@ -543,7 +543,7 @@ class Storage {
       (std::max)(N, sizeof(Allocated) / sizeof(ValueType<A>));
 
   struct Inlined {
-    alignas(ValueType<A>) char inlined_data[sizeof(
+    alignas(ValueType<A>) unsigned char inlined_data[sizeof(
         ValueType<A>[kOptimalInlinedSize])];
   };
 

absl/functional/internal/any_invocable.h

@@ -174,7 +174,7 @@ union TypeErasedState {
   } remote;
 
   // Local-storage for the type-erased object when small and trivial enough
-  alignas(kAlignment) char storage[kStorageSize];
+  alignas(kAlignment) unsigned char storage[kStorageSize];
 };
 
 // A typed accessor for the object in `TypeErasedState` storage

absl/synchronization/mutex_test.cc

@@ -1725,7 +1725,7 @@ TEST(Mutex, Logging) {
 TEST(Mutex, LoggingAddressReuse) {
   // Repeatedly re-create a Mutex with debug logging at the same address.
   ScopedInvariantDebugging scoped_debugging;
-  alignas(absl::Mutex) char storage[sizeof(absl::Mutex)];
+  alignas(absl::Mutex) unsigned char storage[sizeof(absl::Mutex)];
   auto invariant =
       +[](void *alive) { EXPECT_TRUE(*static_cast<bool *>(alive)); };
   constexpr size_t kIters = 10;