SwiftRemoteMirror: Dig into generic SIL boxes

include/swift/Reflection/ReflectionContext.h

@@ -135,6 +135,12 @@ class ReflectionContext
       if (!CDAddr.first)
         return nullptr;
 
+      // FIXME: Non-generic SIL boxes also use the HeapLocalVariable metadata
+      // kind, but with a null capture descriptor right now (see
+      // FixedBoxTypeInfoBase::allocate).
+      //
+      // Non-generic SIL boxes share metadata among types with compatible
+      // layout, but we need some way to get an outgoing pointer map for them.
       auto *CD = getBuilder().getCaptureDescriptor(CDAddr.second);
       if (CD == nullptr)
         return nullptr;
@@ -144,9 +150,16 @@ class ReflectionContext
       return getClosureContextInfo(ObjectAddress, Info);
     }
 
-    case MetadataKind::HeapGenericLocalVariable:
-      // SIL @box type
+    case MetadataKind::HeapGenericLocalVariable: {
+      // Generic SIL @box type - there is always an instantiated metadata
+      // pointer for the boxed type.
+      if (auto Meta = readMetadata(MetadataAddress.second)) {
+        auto GenericHeapMeta =
+          cast<TargetGenericBoxHeapMetadata<Runtime>>(Meta.getLocalBuffer());
+        return getMetadataTypeInfo(GenericHeapMeta->BoxedType);
+      }
       return nullptr;
+    }
 
     case MetadataKind::ErrorObject:
       // ErrorProtocol boxed existential on non-Objective-C runtime target

include/swift/Remote/MetadataReader.h

@@ -957,7 +957,7 @@ class MetadataReader {
       case MetadataKind::Function:
         return _readMetadata<TargetFunctionTypeMetadata>(address);
       case MetadataKind::HeapGenericLocalVariable:
-        return _readMetadata<TargetHeapLocalVariableMetadata>(address);
+        return _readMetadata<TargetGenericBoxHeapMetadata>(address);
       case MetadataKind::HeapLocalVariable:
         return _readMetadata<TargetHeapLocalVariableMetadata>(address);
       case MetadataKind::Metatype:

include/swift/Runtime/Metadata.h

@@ -31,6 +31,7 @@
 #include "swift/Basic/Malloc.h"
 #include "swift/Basic/FlaggedPointer.h"
 #include "swift/Basic/RelativePointer.h"
+#include "../../../stdlib/public/SwiftShims/HeapObject.h"
 
 namespace swift {
 
@@ -2494,6 +2495,63 @@ struct TargetGenericMetadata {
 };
 using GenericMetadata = TargetGenericMetadata<InProcess>;
 
+/// Heap metadata for a box, which may have been generated statically by the
+/// compiler or by the runtime.
+template <typename Runtime>
+struct TargetBoxHeapMetadata : public TargetHeapMetadata<Runtime> {
+  /// The offset from the beginning of a box to its value.
+  unsigned Offset;
+
+  constexpr TargetBoxHeapMetadata(MetadataKind kind, unsigned offset)
+  : TargetHeapMetadata<Runtime>(kind), Offset(offset) {}
+};
+using BoxHeapMetadata = TargetBoxHeapMetadata<InProcess>;
+
+/// Heap metadata for runtime-instantiated generic boxes.
+template <typename Runtime>
+struct TargetGenericBoxHeapMetadata : public TargetBoxHeapMetadata<Runtime> {
+  using super = TargetBoxHeapMetadata<Runtime>;
+  using super::Offset;
+
+  /// The type inside the box.
+  ConstTargetMetadataPointer<Runtime, TargetMetadata> BoxedType;
+
+  constexpr
+  TargetGenericBoxHeapMetadata(MetadataKind kind, unsigned offset,
+    ConstTargetMetadataPointer<Runtime, TargetMetadata> boxedType)
+  : TargetBoxHeapMetadata<Runtime>(kind, offset), BoxedType(boxedType)
+  {}
+
+  static unsigned getHeaderOffset(const Metadata *boxedType) {
+    // Round up the header size to alignment.
+    unsigned alignMask = boxedType->getValueWitnesses()->getAlignmentMask();
+    return (sizeof(HeapObject) + alignMask) & ~alignMask;
+  }
+
+  /// Project the value out of a box of this type.
+  OpaqueValue *project(HeapObject *box) const {
+    auto bytes = reinterpret_cast<char*>(box);
+    return reinterpret_cast<OpaqueValue *>(bytes + Offset);
+  }
+
+  /// Get the allocation size of this box.
+  unsigned getAllocSize() const {
+    return Offset + BoxedType->getValueWitnesses()->getSize();
+  }
+
+  /// Get the allocation alignment of this box.
+  unsigned getAllocAlignMask() const {
+    // Heap allocations are at least pointer aligned.
+    return BoxedType->getValueWitnesses()->getAlignmentMask()
+    | (alignof(void*) - 1);
+  }
+
+  static bool classof(const TargetMetadata<Runtime> *metadata) {
+    return metadata->getKind() == MetadataKind::HeapGenericLocalVariable;
+  }
+};
+using GenericBoxHeapMetadata = TargetGenericBoxHeapMetadata<InProcess>;
+
 /// \brief The control structure of a generic or resilient protocol
 /// conformance.
 ///

stdlib/public/runtime/HeapObject.cpp

@@ -133,57 +133,6 @@ SWIFT_RUNTIME_EXPORT
 extern "C" intptr_t swift_bufferHeaderSize() { return sizeof(HeapObject); }
 
 namespace {
-/// Heap metadata for a box, which may have been generated statically by the
-/// compiler or by the runtime.
-struct BoxHeapMetadata : public HeapMetadata {
-  /// The offset from the beginning of a box to its value.
-  unsigned Offset;
-
-  constexpr BoxHeapMetadata(MetadataKind kind,
-                            unsigned offset)
-    : HeapMetadata{kind}, Offset(offset)
-  {}
-
-
-};
-
-/// Heap metadata for runtime-instantiated generic boxes.
-struct GenericBoxHeapMetadata : public BoxHeapMetadata {
-  /// The type inside the box.
-  const Metadata *BoxedType;
-
-  constexpr GenericBoxHeapMetadata(MetadataKind kind,
-                                   unsigned offset,
-                                   const Metadata *boxedType)
-    : BoxHeapMetadata{kind, offset},
-      BoxedType(boxedType)
-  {}
-
-  static unsigned getHeaderOffset(const Metadata *boxedType) {
-    // Round up the header size to alignment.
-    unsigned alignMask = boxedType->getValueWitnesses()->getAlignmentMask();
-    return (sizeof(HeapObject) + alignMask) & ~alignMask;
-  }
-
-  /// Project the value out of a box of this type.
-  OpaqueValue *project(HeapObject *box) const {
-    auto bytes = reinterpret_cast<char*>(box);
-    return reinterpret_cast<OpaqueValue *>(bytes + Offset);
-  }
-
-  /// Get the allocation size of this box.
-  unsigned getAllocSize() const {
-    return Offset + BoxedType->getValueWitnesses()->getSize();
-  }
-
-  /// Get the allocation alignment of this box.
-  unsigned getAllocAlignMask() const {
-    // Heap allocations are at least pointer aligned.
-    return BoxedType->getValueWitnesses()->getAlignmentMask()
-      | (alignof(void*) - 1);
-  }
-};
-
 /// Heap object destructor for a generic box allocated with swift_allocBox.
 static void destroyGenericBox(HeapObject *o) {
   auto metadata = static_cast<const GenericBoxHeapMetadata *>(o->metadata);