[utils] Deprecate modm::aligned_storage_t

Deprecate modm::aligned_storage_t which relies on the deprecated type
std::aligned_storage. Remove all usages from modm and replace
them with a properly aligned std::byte array as recommended by C++ paper
P1413R3.

Author: chris-durand

src/modm/utils/aligned_storage.hpp

@@ -51,6 +51,9 @@ union aligned_storage_helper
 };
 } // namespace aligned_storage_impl
 
+template<std::size_t Cap>
+constexpr auto default_storage_alignment = alignof(aligned_storage_impl::aligned_storage_helper<Cap>);
+
 /**
  * Implementation of std::aligned_storage that avoids GCC bug #61458 which can
  * cause excessive size for types smaller than the maximum alignment.
@@ -59,15 +62,20 @@ union aligned_storage_helper
  * The implementation is derived from:
  * https://github.com/WG21-SG14/SG14/blob/master/SG14/inplace_function.h
  */
-template<size_t Cap, size_t Align = alignof(aligned_storage_impl::aligned_storage_helper<Cap>)>
-struct aligned_storage {
-    using type = std::aligned_storage_t<Cap, Align>;
+template<std::size_t Cap, std::size_t Align = default_storage_alignment<Cap>>
+struct [[deprecated("see C++ standards paper P1413R3")]] aligned_storage // DEPRECATED: 2026q3
+{
+    struct type
+    {
+        alignas(Align) unsigned char data[Cap];
+    };
 };
 /// @endcond
 
 /// @ingroup modm_utils
-template<size_t Cap, size_t Align = alignof(aligned_storage_impl::aligned_storage_helper<Cap>)>
-using aligned_storage_t = typename aligned_storage<Cap, Align>::type;
+template<std::size_t Cap, std::size_t Align = default_storage_alignment<Cap>>
+using aligned_storage_t [[deprecated("see C++ standards paper P1413R3")]] =
+	typename aligned_storage<Cap, Align>::type; // DEPRECATED: 2026q3
 
 static_assert(sizeof(aligned_storage_t<sizeof(void*)>) == sizeof(void*));
 static_assert(alignof(aligned_storage_t<sizeof(void*)>) == alignof(void*));

src/modm/utils/inplace_any.hpp

@@ -207,7 +207,7 @@ class inplace_any final
     void move_from(inplace_any<S>&& other) noexcept;
 
 private:
-    modm::aligned_storage<Size>::type storage_;
+    alignas(default_storage_alignment<Size>) std::byte storage_[Size];
     inplace_any_impl::HandlerFunc handler_{nullptr};
 };
 

src/modm/utils/inplace_function.hpp

@@ -26,6 +26,7 @@
 
 #pragma once
 
+#include <cstddef>
 #include <type_traits>
 #include <utility>
 #include <functional>
@@ -118,7 +119,7 @@ struct is_valid_inplace_dst : std::true_type
 template<
     class Signature,
     size_t Capacity = inplace_function_detail::InplaceFunctionDefaultCapacity,
-    size_t Alignment = alignof(modm::aligned_storage_t<Capacity>)
+    size_t Alignment = default_storage_alignment<Capacity>
 >
 class inplace_function; // unspecified
 
@@ -140,7 +141,6 @@ template<
 >
 class inplace_function<R(Args...), Capacity, Alignment>
 {
-    using storage_t = modm::aligned_storage_t<Capacity, Alignment>;
     using vtable_t = inplace_function_detail::vtable<R, Args...>;
     using vtable_ptr_t = const vtable_t*;
 
@@ -275,7 +275,7 @@ class inplace_function<R(Args...), Capacity, Alignment>
     {
         if (this == std::addressof(other)) return;
 
-        storage_t tmp;
+        alignas(Alignment) std::byte tmp[Capacity];
         vtable_ptr_->relocate_ptr(
             std::addressof(tmp),
             std::addressof(storage_)
@@ -301,7 +301,7 @@ class inplace_function<R(Args...), Capacity, Alignment>
 
 private:
     vtable_ptr_t vtable_ptr_;
-    mutable storage_t storage_;
+    alignas(Alignment) mutable std::byte storage_[Capacity];
 
     inplace_function(
         vtable_ptr_t vtable_ptr,

test/modm/utils/inplace_function_test.cpp

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2026, Christopher Durand
+ *
+ * This file is part of the modm project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+// ----------------------------------------------------------------------------
+
+#include "inplace_function_test.hpp"
+#include <modm/utils/inplace_function.hpp>
+
+void
+InplaceFunctionTest::testCall()
+{
+	int value = 0;
+
+	modm::inplace_function<int(int), 8> func = [&value](int x) {
+		value = x;
+		return x * 2;
+	};
+
+	TEST_ASSERT_EQUALS(func(42), 84);
+	TEST_ASSERT_EQUALS(value, 42);
+}

test/modm/utils/inplace_function_test.hpp

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2026, Christopher Durand
+ *
+ * This file is part of the modm project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+// ----------------------------------------------------------------------------
+
+#include <unittest/testsuite.hpp>
+
+/// @ingroup modm_test_test_utils
+class InplaceFunctionTest : public unittest::TestSuite
+{
+public:
+	void
+	testCall();
+};