fix zero initial size for memory resource parent

Author: pknowles

include/decodeless/allocator.hpp

@@ -71,7 +71,7 @@ class linear_memory_resource {
     linear_memory_resource(size_t initialSize, ResOrAlloc&& parent)
         requires memory_resource<ResOrAlloc>
         : m_parent(std::move(parent))
-        , m_begin(allocate_bytes(m_parent, initialSize))
+        , m_begin(initialSize != 0 ? allocate_bytes(m_parent, initialSize) : initialSize)
         , m_next(reinterpret_cast<uintptr_t>(m_begin))
         , m_end(reinterpret_cast<uintptr_t>(m_begin) + initialSize) {
         if constexpr (nonrealloc_memory_resource<ResOrAlloc>) {

test/src/allocator.cpp

@@ -203,12 +203,30 @@ TEST_F(Allocate, EmptyNonrealloc) {
     EXPECT_EQ(memory.capacity(), 42);
 }
 
-TEST_F(Allocate, EmptyRealloc) {
+TEST_F(Allocate, EmptyReallocDefault) {
     linear_memory_resource<ReallocNullAllocator> memory;
     EXPECT_EQ(memory.size(), 0);
     EXPECT_EQ(memory.capacity(), 0);
 }
 
+TEST_F(Allocate, EmptyRealloc) {
+    linear_memory_resource<ReallocNullMemoryResource> memory{ReallocNullMemoryResource()};
+    EXPECT_EQ(memory.size(), 0);
+    EXPECT_EQ(memory.capacity(), 0);
+}
+
+TEST_F(Allocate, ZeroInitialRealloc) {
+    linear_memory_resource<ReallocNullAllocator> memory{0, ReallocNullAllocator()};
+    EXPECT_EQ(memory.size(), 0);
+    EXPECT_EQ(memory.capacity(), 0);
+}
+
+TEST_F(Allocate, ZeroInitialReallocMemoryResource) {
+    linear_memory_resource<ReallocNullMemoryResource> memory{0, ReallocNullMemoryResource()};
+    EXPECT_EQ(memory.size(), 0);
+    EXPECT_EQ(memory.capacity(), 0);
+}
+
 TEST_F(Allocate, Truncate) {
     linear_memory_resource<ReallocNullAllocator> memory;
     std::ignore = memory.allocate(1, 1);