Fix bug where calling a list setter using a list obtained from a similarly-typed…

Fix bug where calling a list setter using a list obtained from a similarly-typed getter, but where the underlying pointer was null, would write an incorrectly-typed pointer in the destination (specifically, an empty List(Void)). Now it sets an empty list of the correct type.

c++/src/capnp/any.h

@@ -388,7 +388,7 @@ struct List<AnyPointer, Kind::OTHER> {
   public:
     typedef List<AnyPointer> Reads;
 
-    Reader() = default;
+    inline Reader(): reader(ElementSize::POINTER) {}
     inline explicit Reader(_::ListReader reader): reader(reader) {}
 
     inline uint size() const { return reader.size() / ELEMENTS; }
@@ -417,7 +417,7 @@ struct List<AnyPointer, Kind::OTHER> {
     typedef List<AnyPointer> Builds;
 
     Builder() = delete;
-    inline Builder(decltype(nullptr)) {}
+    inline Builder(decltype(nullptr)): builder(ElementSize::POINTER) {}
     inline explicit Builder(_::ListBuilder builder): builder(builder) {}
 
     inline operator Reader() { return Reader(builder.asReader()); }
@@ -546,7 +546,7 @@ class List<AnyStruct, Kind::OTHER>::Reader {
 public:
   typedef List<AnyStruct> Reads;
 
-  Reader() = default;
+  inline Reader(): reader(ElementSize::INLINE_COMPOSITE) {}
   inline explicit Reader(_::ListReader reader): reader(reader) {}
 
   inline uint size() const { return reader.size() / ELEMENTS; }
@@ -575,7 +575,7 @@ public:
   typedef List<AnyStruct> Builds;
 
   Builder() = delete;
-  inline Builder(decltype(nullptr)) {}
+  inline Builder(decltype(nullptr)): builder(ElementSize::INLINE_COMPOSITE) {}
   inline explicit Builder(_::ListBuilder builder): builder(builder) {}
 
   inline operator Reader() { return Reader(builder.asReader()); }
@@ -602,7 +602,7 @@ private:
 
 class AnyList::Reader {
 public:
-  Reader() = default;
+  inline Reader(): _reader(ElementSize::VOID) {}
   inline Reader(_::ListReader reader): _reader(reader) {}
 
 #if !_MSC_VER  // TODO(msvc): MSVC ICEs on this. Try restoring when compiler improves.
@@ -635,7 +635,7 @@ private:
 
 class AnyList::Builder {
 public:
-  inline Builder(decltype(nullptr)) {}
+  inline Builder(decltype(nullptr)): _builder(ElementSize::VOID) {}
   inline Builder(_::ListBuilder builder): _builder(builder) {}
 
 #if !_MSC_VER  // TODO(msvc): MSVC ICEs on this. Try restoring when compiler improves.

c++/src/capnp/dynamic.h

@@ -351,7 +351,7 @@ class DynamicList::Reader {
 public:
   typedef DynamicList Reads;
 
-  Reader() = default;
+  inline Reader(): reader(ElementSize::VOID) {}
 
   template <typename T, typename = kj::EnableIf<kind<FromReader<T>>() == Kind::LIST>>
   inline Reader(T&& value): Reader(toDynamic(value)) {}
@@ -392,8 +392,8 @@ class DynamicList::Builder {
 public:
   typedef DynamicList Builds;
 
-  Builder() = default;
-  inline Builder(decltype(nullptr)) {}
+  inline Builder(): builder(ElementSize::VOID) {}
+  inline Builder(decltype(nullptr)): builder(ElementSize::VOID) {}
 
   template <typename T, typename = kj::EnableIf<kind<FromBuilder<T>>() == Kind::LIST>>
   inline Builder(T&& value): Builder(toDynamic(value)) {}

c++/src/capnp/encoding-test.c++

@@ -516,6 +516,80 @@ TEST(Encoding, SmallStructLists) {
   }
 }
 
+TEST(Encoding, SetListToEmpty) {
+  // Test initializing list fields from various ways of constructing zero-sized lists.
+  // At one point this would often fail because the lists would have ElementSize::VOID which is
+  // incompatible with other list sizes.
+
+#define ALL_LIST_TYPES(MACRO) \
+  MACRO(Void, Void) \
+  MACRO(Bool, bool) \
+  MACRO(UInt8, uint8_t) \
+  MACRO(UInt16, uint16_t) \
+  MACRO(UInt32, uint32_t) \
+  MACRO(UInt64, uint64_t) \
+  MACRO(Int8, int8_t) \
+  MACRO(Int16, int16_t) \
+  MACRO(Int32, int32_t) \
+  MACRO(Int64, int64_t) \
+  MACRO(Float32, float) \
+  MACRO(Float64, double) \
+  MACRO(Text, Text) \
+  MACRO(Data, Data) \
+  MACRO(Struct, TestAllTypes)
+
+#define SET_FROM_READER_ACCESSOR(name, type) \
+  root.set##name##List(reader.get##name##List());
+
+#define SET_FROM_BUILDER_ACCESSOR(name, type) \
+  root.set##name##List(root.get##name##List());
+
+#define SET_FROM_READER_CONSTRUCTOR(name, type) \
+  root.set##name##List(List<type>::Reader());
+
+#define SET_FROM_BUILDER_CONSTRUCTOR(name, type) \
+  root.set##name##List(List<type>::Builder());
+
+#define CHECK_EMPTY_NONNULL(name, type) \
+  EXPECT_TRUE(root.has##name##List()); \
+  EXPECT_EQ(0, root.get##name##List().size());
+
+  {
+    MallocMessageBuilder builder;
+    auto root = builder.initRoot<test::TestAllTypes>();
+    auto reader = root.asReader();
+    ALL_LIST_TYPES(SET_FROM_READER_ACCESSOR)
+    ALL_LIST_TYPES(CHECK_EMPTY_NONNULL)
+  }
+
+  {
+    MallocMessageBuilder builder;
+    auto root = builder.initRoot<test::TestAllTypes>();
+    ALL_LIST_TYPES(SET_FROM_BUILDER_ACCESSOR)
+    ALL_LIST_TYPES(CHECK_EMPTY_NONNULL)
+  }
+
+  {
+    MallocMessageBuilder builder;
+    auto root = builder.initRoot<test::TestAllTypes>();
+    ALL_LIST_TYPES(SET_FROM_READER_CONSTRUCTOR)
+    ALL_LIST_TYPES(CHECK_EMPTY_NONNULL)
+  }
+
+  {
+    MallocMessageBuilder builder;
+    auto root = builder.initRoot<test::TestAllTypes>();
+    ALL_LIST_TYPES(SET_FROM_BUILDER_CONSTRUCTOR)
+    ALL_LIST_TYPES(CHECK_EMPTY_NONNULL)
+  }
+
+#undef SET_FROM_READER_ACCESSOR
+#undef SET_FROM_BUILDER_ACCESSOR
+#undef SET_FROM_READER_CONSTRUCTOR
+#undef SET_FROM_BUILDER_CONSTRUCTOR
+#undef CHECK_EMPTY_NONNULL
+}
+
 // =======================================================================================
 
 TEST(Encoding, ListUpgrade) {

c++/src/capnp/layout.c++

@@ -1073,7 +1073,7 @@ struct WireHelpers {
     useDefault:
       if (defaultValue == nullptr ||
           reinterpret_cast<const WirePointer*>(defaultValue)->isNull()) {
-        return ListBuilder();
+        return ListBuilder(elementSize);
       }
       origRefTarget = copyMessage(
           origSegment, origRef, reinterpret_cast<const WirePointer*>(defaultValue));
@@ -1195,7 +1195,7 @@ struct WireHelpers {
     useDefault:
       if (defaultValue == nullptr ||
           reinterpret_cast<const WirePointer*>(defaultValue)->isNull()) {
-        return ListBuilder();
+        return ListBuilder(ElementSize::VOID);
       }
       origRefTarget = copyMessage(
           origSegment, origRef, reinterpret_cast<const WirePointer*>(defaultValue));
@@ -1248,7 +1248,7 @@ struct WireHelpers {
     useDefault:
       if (defaultValue == nullptr ||
           reinterpret_cast<const WirePointer*>(defaultValue)->isNull()) {
-        return ListBuilder();
+        return ListBuilder(ElementSize::INLINE_COMPOSITE);
       }
       origRefTarget = copyMessage(
           origSegment, origRef, reinterpret_cast<const WirePointer*>(defaultValue));
@@ -1905,7 +1905,7 @@ struct WireHelpers {
     useDefault:
       if (defaultValue == nullptr ||
           reinterpret_cast<const WirePointer*>(defaultValue)->isNull()) {
-        return ListReader();
+        return ListReader(expectedElementSize);
       }
       segment = nullptr;
       ref = reinterpret_cast<const WirePointer*>(defaultValue);

c++/src/capnp/layout.h

@@ -562,16 +562,16 @@ private:
 
 class ListBuilder: public kj::DisallowConstCopy {
 public:
-  inline ListBuilder()
+  inline explicit ListBuilder(ElementSize elementSize)
       : segment(nullptr), ptr(nullptr), elementCount(0 * ELEMENTS),
-        step(0 * BITS / ELEMENTS), elementSize(ElementSize::VOID) {}
+        step(0 * BITS / ELEMENTS), elementSize(elementSize) {}
 
   MSVC_DEFAULT_ASSIGNMENT_WORKAROUND(, ListBuilder)
 
   inline word* getLocation() {
     // Get the object's location.
 
-    if (elementSize == ElementSize::INLINE_COMPOSITE) {
+    if (elementSize == ElementSize::INLINE_COMPOSITE && ptr != nullptr) {
       return reinterpret_cast<word*>(ptr) - POINTER_SIZE_IN_WORDS;
     } else {
       return reinterpret_cast<word*>(ptr);
@@ -640,9 +640,10 @@ private:
 
 class ListReader {
 public:
-  inline ListReader()
+  inline explicit ListReader(ElementSize elementSize)
       : segment(nullptr), ptr(nullptr), elementCount(0), step(0 * BITS / ELEMENTS),
-        structDataSize(0), structPointerCount(0), nestingLimit(0x7fffffff) {}
+        structDataSize(0), structPointerCount(0), elementSize(elementSize),
+        nestingLimit(0x7fffffff) {}
 
   MSVC_DEFAULT_ASSIGNMENT_WORKAROUND(const, ListReader)
 

c++/src/capnp/list.h

@@ -111,7 +111,7 @@ struct List<T, Kind::PRIMITIVE> {
   public:
     typedef List<T> Reads;
 
-    Reader() = default;
+    inline Reader(): reader(_::elementSizeForType<T>()) {}
     inline explicit Reader(_::ListReader reader): reader(reader) {}
 
     inline uint size() const { return reader.size() / ELEMENTS; }
@@ -139,7 +139,7 @@ struct List<T, Kind::PRIMITIVE> {
   public:
     typedef List<T> Builds;
 
-    Builder() = delete;
+    inline Builder(): builder(_::elementSizeForType<T>()) {}
     inline Builder(decltype(nullptr)) {}
     inline explicit Builder(_::ListBuilder builder): builder(builder) {}
 
@@ -207,7 +207,7 @@ struct List<T, Kind::STRUCT> {
   public:
     typedef List<T> Reads;
 
-    Reader() = default;
+    inline Reader(): reader(ElementSize::INLINE_COMPOSITE) {}
     inline explicit Reader(_::ListReader reader): reader(reader) {}
 
     inline uint size() const { return reader.size() / ELEMENTS; }
@@ -235,7 +235,7 @@ struct List<T, Kind::STRUCT> {
   public:
     typedef List<T> Builds;
 
-    Builder() = delete;
+    inline Builder(): builder(ElementSize::INLINE_COMPOSITE) {}
     inline Builder(decltype(nullptr)) {}
     inline explicit Builder(_::ListBuilder builder): builder(builder) {}
 
@@ -325,7 +325,7 @@ struct List<List<T>, Kind::LIST> {
   public:
     typedef List<List<T>> Reads;
 
-    Reader() = default;
+    inline Reader(): reader(ElementSize::POINTER) {}
     inline explicit Reader(_::ListReader reader): reader(reader) {}
 
     inline uint size() const { return reader.size() / ELEMENTS; }
@@ -354,7 +354,7 @@ struct List<List<T>, Kind::LIST> {
   public:
     typedef List<List<T>> Builds;
 
-    Builder() = delete;
+    inline Builder(): builder(ElementSize::POINTER) {}
     inline Builder(decltype(nullptr)) {}
     inline explicit Builder(_::ListBuilder builder): builder(builder) {}
 
@@ -434,7 +434,7 @@ struct List<T, Kind::BLOB> {
   public:
     typedef List<T> Reads;
 
-    Reader() = default;
+    inline Reader(): reader(ElementSize::POINTER) {}
     inline explicit Reader(_::ListReader reader): reader(reader) {}
 
     inline uint size() const { return reader.size() / ELEMENTS; }
@@ -462,7 +462,7 @@ struct List<T, Kind::BLOB> {
   public:
     typedef List<T> Builds;
 
-    Builder() = delete;
+    inline Builder(): builder(ElementSize::POINTER) {}
     inline Builder(decltype(nullptr)) {}
     inline explicit Builder(_::ListBuilder builder): builder(builder) {}