[lldb] Factor out iteration over runtime types from GetChildCompilerTypeAtIndex()

This patch introduces a new class SwiftRuntimeTypeVisitor that exists
to unify iteration over runtime type information. The visitor callback
has closure parameters that can be called to make additional expensive
queries on a child.

TODO: This is not the final evolution step.

- We probably should remove the "depth" parameter entirely and implement the access path computation for GetIndexOfChildMemberWithName at a different layer.

- We could cache the results for the last execution context.

Relanding with an off-by-one error fixed in
GetExistentialSyntheticChildren that was caught by ASAN!

(cherry picked from commit 4c6a22a)

Author: adrian-prantl

lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntimeDynamicTypeResolution.cpp

@@ -667,16 +667,30 @@ GetExistentialSyntheticChildren(TypeSystemSwiftTypeRef &ts,
       llvm::dyn_cast<swift::reflection::ProtocolCompositionTypeRef>(tr);
   if (!protocol_composition_tr)
     return children;
-  if (ti && (llvm::isa<swift::reflection::ReferenceTypeInfo>(ti) ||
-             llvm::isa<swift::reflection::RecordTypeInfo>(ti))) {
+  if (!ti)
+    return children;
+  auto *rti = llvm::dyn_cast<swift::reflection::RecordTypeInfo>(ti);
+  if (rti || llvm::isa<swift::reflection::ReferenceTypeInfo>(ti)) {
     TypeSystemSwiftTypeRefSP ts_sp = ts.GetTypeSystemSwiftTypeRef();
     children.push_back({"object", [=]() {
                           if (auto *super_class_tr =
                                   protocol_composition_tr->getSuperclass())
                             return GetTypeFromTypeRef(*ts_sp, super_class_tr);
                           else
-                            return ts_sp->GetRawPointerType();
-    }});
+                            return rti ? ts_sp->GetBuiltinUnknownObjectType()
+                                       : ts_sp->GetBuiltinRawPointerType();
+                        }});
+    // We replaced "object" with a more specific type.
+    if (rti) {
+      auto &fields = rti->getFields();
+      for (unsigned i = 1; i < fields.size(); ++i) {
+        TypeSystemSwiftTypeRefSP ts_sp = ts.GetTypeSystemSwiftTypeRef();
+        auto *type_ref = fields[i].TR;
+        children.push_back({fields[i].Name, [=]() {
+                              return GetTypeFromTypeRef(*ts_sp, type_ref);
+                            }});
+      }
+    }
   }
   if (ti && llvm::isa<swift::reflection::RecordTypeInfo>(ti)) {
     auto &fields =

lldb/source/Plugins/TypeSystem/Swift/SwiftASTContext.cpp

@@ -8623,10 +8623,6 @@ std::string SwiftASTContext::GetSwiftName(const clang::Decl *clang_decl,
   return {};
 }
 
-CompilerType SwiftASTContext::GetBuiltinRawPointerType() {
-  return GetTypeFromMangledTypename(ConstString("$sBpD"));
-}
-
 CompilerType
 SwiftASTContext::ConvertClangTypeToSwiftType(CompilerType clang_type) {
   auto ts = GetTypeSystemSwiftTypeRef();

lldb/source/Plugins/TypeSystem/Swift/SwiftASTContext.h

@@ -412,7 +412,6 @@ class SwiftASTContext : public TypeSystemSwift {
   std::string GetSwiftName(const clang::Decl *clang_decl,
                            TypeSystemClang &clang_typesystem) override;
 
-  CompilerType GetBuiltinRawPointerType() override;
   CompilerType GetBuiltinIntType();
 
   /// Attempts to convert a Clang type into a Swift type.

lldb/source/Plugins/TypeSystem/Swift/TypeSystemSwift.cpp

@@ -98,6 +98,14 @@ bool TypeSystemSwift::IsScalarType(opaque_compiler_type_t type) {
   return (GetTypeInfo(type, nullptr) & eTypeIsScalar) != 0;
 }
 
+CompilerType TypeSystemSwift::GetBuiltinRawPointerType() {
+  return GetTypeFromMangledTypename(ConstString("$sBpD"));
+}
+
+CompilerType TypeSystemSwift::GetBuiltinUnknownObjectType() {
+  return GetTypeFromMangledTypename(ConstString("$sBOD"));
+}
+
 bool TypeSystemSwift::ShouldTreatScalarValueAsAddress(
     opaque_compiler_type_t type) {
   return Flags(GetTypeInfo(type, nullptr))

lldb/source/Plugins/TypeSystem/Swift/TypeSystemSwift.h

@@ -197,7 +197,8 @@ class TypeSystemSwift : public TypeSystem {
   virtual std::string GetSwiftName(const clang::Decl *clang_decl,
                                    TypeSystemClang &clang_typesystem) = 0;
 
-  virtual CompilerType GetBuiltinRawPointerType() = 0;
+  CompilerType GetBuiltinRawPointerType();
+  CompilerType GetBuiltinUnknownObjectType();
 
   /// Attempts to convert a Clang type into a Swift type.
   /// For example, int is converted to Int32.

lldb/source/Plugins/TypeSystem/Swift/TypeSystemSwiftTypeRef.cpp

@@ -1444,11 +1444,6 @@ TypeSystemSwiftTypeRef::GetSwiftName(const clang::Decl *clang_decl,
   return {};
 }
 
-CompilerType TypeSystemSwiftTypeRef::GetBuiltinRawPointerType() {
-  return GetTypeFromMangledTypename(ConstString("$sBpD"));
-}
-
-
 static bool IsImportedType(swift::Demangle::NodePointer node) {
   if (!node)
     return false;

lldb/source/Plugins/TypeSystem/Swift/TypeSystemSwiftTypeRef.h

@@ -412,8 +412,6 @@ class TypeSystemSwiftTypeRef : public TypeSystemSwift {
   std::string GetSwiftName(const clang::Decl *clang_decl,
                            TypeSystemClang &clang_typesystem) override;
 
-  CompilerType GetBuiltinRawPointerType() override;
-
   /// Wrap \p node as \p Global(TypeMangling(node)), remangle the type
   /// and create a CompilerType from it.
   CompilerType RemangleAsType(swift::Demangle::Demangler &dem,