[#38] Never allocate Optional Views on heap

* necessary to ensure continuous allocation

runtime/ClangTidySuppressions.txt

@@ -8,12 +8,12 @@ bugprone-signed-char-misuse:src/zserio/DeltaContext.h:257
 bugprone-signed-char-misuse:src/zserio/DeltaContext.h:273
 
 # Optional is a generic container and exceptions may be thrown from the value type.
-bugprone-exception-escape:src/zserio/Optional.h:352
-bugprone-exception-escape:src/zserio/Optional.h:379
+bugprone-exception-escape:src/zserio/Optional.h:357
+bugprone-exception-escape:src/zserio/Optional.h:384
 
 # False positives - has_value() is checked before value().
-bugprone-exception-escape:src/zserio/Optional.h:215
-bugprone-exception-escape:src/zserio/Optional.h:399
+bugprone-exception-escape:src/zserio/Optional.h:220
+bugprone-exception-escape:src/zserio/Optional.h:404
 
 # Variant is a generic container and exceptions may be thrown from the element types.
 bugprone-exception-escape:src/zserio/Variant.h:242
@@ -27,7 +27,7 @@ bugprone-use-after-move:src/zserio/Variant.h:681
 cert-dcl58-cpp:src/zserio/BitBuffer.h:587
 cert-dcl58-cpp:src/zserio/BitBuffer.h:599
 cert-dcl58-cpp:src/zserio/Extended.h:203
-cert-dcl58-cpp:src/zserio/Optional.h:1165
+cert-dcl58-cpp:src/zserio/Optional.h:1170
 cert-dcl58-cpp:src/zserio/Variant.h:841
 cert-dcl58-cpp:src/zserio/View.h:223
 
@@ -46,14 +46,14 @@ cppcoreguidelines-macro-usage:src/zserio/CppRuntimeVersion.h:8
 cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/CppRuntimeException.h:193
 
 # Optional follows std::optional so passing value by const & is correct.
-cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:577
-cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:594
-cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:794
-cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:808
-cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:934
-cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:948
-cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:1006
-cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:1020
+cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:582
+cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:599
+cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:799
+cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:813
+cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:939
+cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:953
+cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:1011
+cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Optional.h:1025
 
 # This is necessary for low level implementation of Span to mimic standard C++20 'std::span' abstraction.
 cppcoreguidelines-pro-bounds-array-to-pointer-decay:src/zserio/Span.h:113
@@ -85,10 +85,10 @@ cppcoreguidelines-pro-type-reinterpret-cast:src/zserio/FileUtil.cpp:19
 cppcoreguidelines-pro-type-reinterpret-cast:src/zserio/FileUtil.cpp:49
 
 # Optional follows std::optional so the ctors should be implicit.
-google-explicit-constructor:src/zserio/Optional.h:117
-google-explicit-constructor:src/zserio/Optional.h:127
-google-explicit-constructor:src/zserio/Optional.h:137
-google-explicit-constructor:src/zserio/Optional.h:238
+google-explicit-constructor:src/zserio/Optional.h:122
+google-explicit-constructor:src/zserio/Optional.h:132
+google-explicit-constructor:src/zserio/Optional.h:142
+google-explicit-constructor:src/zserio/Optional.h:243
 
 # This is necessary for low level implementation of Span to mimic standard C++20 'std::span' abstraction.
 google-explicit-constructor:src/zserio/Span.h:112
@@ -110,7 +110,7 @@ google-readability-casting:src/zserio/Variant.h:66
 google-explicit-constructor:src/zserio/View.h:133
 
 # Intentional tests.
-bugprone-exception-escape:test/zserio/OptionalTest.cpp:284
+bugprone-exception-escape:test/zserio/OptionalTest.cpp:75
 bugprone-exception-escape:test/zserio/VariantTest.cpp:35
 cppcoreguidelines-avoid-c-arrays:test/zserio/SpanTest.cpp:45
 cppcoreguidelines-special-member-functions:test/zserio/VariantTest.cpp:32

runtime/src/zserio/Optional.h

@@ -7,6 +7,7 @@
 #include "zserio/CppRuntimeException.h"
 #include "zserio/HashCodeUtil.h"
 #include "zserio/Traits.h"
+#include "zserio/View.h"
 
 namespace zserio
 {
@@ -45,6 +46,10 @@ template <typename T>
 struct is_optional_heap_allocated : is_optional_heap_allocated_impl<T>
 {};
 
+template <typename T>
+struct is_optional_heap_allocated<View<T>> : std::false_type
+{};
+
 template <typename T>
 constexpr bool is_optional_heap_allocated_v = is_optional_heap_allocated<T>::value;
 

runtime/test/zserio/OptionalTest.cpp

@@ -7,6 +7,7 @@
 #include "zserio/Optional.h"
 #include "zserio/TrackingAllocator.h"
 #include "zserio/Types.h"
+#include "zserio/View.h"
 
 namespace zserio
 {
@@ -47,6 +48,53 @@ struct BigObj
     std::array<char, 30> data;
 };
 
+template <>
+class View<BigObj>
+{
+public:
+    explicit View(const BigObj& data, std::array<char, 30> param) :
+            m_data(data),
+            m_param(param)
+    {}
+
+    const std::array<char, 30>& param() const
+    {
+        return m_param;
+    }
+
+    const BigObj& zserioData() const
+    {
+        return m_data;
+    }
+
+private:
+    const BigObj& m_data;
+    std::array<char, 30> m_param;
+};
+
+struct Recursive
+{
+    using IS_RECURSIVE = int;
+    Optional<Recursive> next;
+};
+
+template <>
+class View<Recursive>
+{
+public:
+    explicit View(const Recursive& data) :
+            m_data(data)
+    {}
+
+    const Recursive& zserioData() const
+    {
+        return m_data;
+    }
+
+private:
+    const Recursive& m_data;
+};
+
 template <class ALLOC>
 class OptionalTest : public testing::Test
 {
@@ -279,22 +327,29 @@ TYPED_TEST(OptionalTest, optionalInOptional)
     ASSERT_EQ("test", stringOpt.value().value());
 }
 
+TYPED_TEST(OptionalTest, bigObjOpt)
+{
+    ASSERT_TRUE(detail::is_optional_heap_allocated_v<BigObj>);
+    ASSERT_FALSE(detail::is_optional_heap_allocated_v<View<BigObj>>);
+
+    Optional<BigObj> opt;
+    opt = BigObj();
+    ASSERT_TRUE(opt.has_value());
+    ASSERT_TRUE(std::as_const(opt).has_value());
+}
+
 TYPED_TEST(OptionalTest, recursiveOpt)
 {
-    struct Tmp
-    {
-        using IS_RECURSIVE = int;
-        Optional<Tmp> next;
-    };
-    ASSERT_TRUE(detail::is_optional_heap_allocated_v<Tmp>);
-    Optional<Tmp> opt1;
-    opt1 = Tmp();
-    ASSERT_TRUE(opt1.has_value());
-    ASSERT_TRUE(!opt1->next.has_value());
-    ASSERT_TRUE(!std::as_const(opt1)->next.has_value());
-    opt1->next = Tmp();
-    ASSERT_TRUE(opt1->next.has_value());
-    ASSERT_TRUE(!opt1->next->next.has_value());
+    ASSERT_TRUE(detail::is_optional_heap_allocated_v<Recursive>);
+    ASSERT_FALSE(detail::is_optional_heap_allocated_v<View<Recursive>>);
+    Optional<Recursive> opt;
+    opt = Recursive();
+    ASSERT_TRUE(opt.has_value());
+    ASSERT_TRUE(!opt->next.has_value());
+    ASSERT_TRUE(!std::as_const(opt)->next.has_value());
+    opt->next = Recursive();
+    ASSERT_TRUE(opt->next.has_value());
+    ASSERT_TRUE(!opt->next->next.has_value());
 }
 
 TYPED_TEST(OptionalTest, errors)