[lldb] Identify Swift-implemented ObjC classes

Classes implemented in Swift can be exposed to ObjC. For those classes, the ObjC
metadata is incomplete. Specifically, the encoded types of the ivars are incomplete. As
one might expect, the Swift metadata _is_ complete. In such cases, the Swift runtime
should be consulted when determining the dynamic type of a value.

Differential Revision: https://reviews.llvm.org/D152837

Author: kastiglione

lldb/include/lldb/Target/LanguageRuntime.h

@@ -67,6 +67,12 @@ class LanguageRuntime : public Runtime, public PluginInterface {
 
   virtual lldb::LanguageType GetLanguageType() const = 0;
 
+  /// Return the preferred language runtime instance, which in most cases will
+  /// be the current instance.
+  virtual LanguageRuntime *GetPreferredLanguageRuntime(ValueObject &in_value) {
+    return nullptr;
+  }
+
   virtual bool GetObjectDescription(Stream &str, ValueObject &object) = 0;
 
   virtual bool GetObjectDescription(Stream &str, Value &value,

lldb/source/Core/ValueObjectDynamicValue.cpp

@@ -181,7 +181,18 @@ bool ValueObjectDynamicValue::UpdateValue() {
       known_type != lldb::eLanguageTypeUnknown &&
       known_type != lldb::eLanguageTypeC) {
     runtime = process->GetLanguageRuntime(known_type);
-    if (runtime)
+    if (auto *preferred_runtime =
+            runtime->GetPreferredLanguageRuntime(*m_parent)) {
+      // Try the preferred runtime first.
+      found_dynamic_type = preferred_runtime->GetDynamicTypeAndAddress(
+          *m_parent, m_use_dynamic, class_type_or_name, dynamic_address,
+          value_type);
+      if (found_dynamic_type)
+        // Set the operative `runtime` for later use in this function.
+        runtime = preferred_runtime;
+    }
+    if (!found_dynamic_type)
+      // Fallback to the runtime for `known_type`.
       found_dynamic_type = runtime->GetDynamicTypeAndAddress(
           *m_parent, m_use_dynamic, class_type_or_name, dynamic_address,
           value_type);

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.cpp

@@ -10,8 +10,10 @@
 
 #include "lldb/Expression/FunctionCaller.h"
 #include "lldb/Target/ABI.h"
+#include "lldb/Target/Language.h"
 #include "lldb/Utility/LLDBLog.h"
 #include "lldb/Utility/Log.h"
+#include "lldb/lldb-enumerations.h"
 
 using namespace lldb;
 using namespace lldb_private;
@@ -668,6 +670,19 @@ uint64_t ClassDescriptorV2::GetInstanceSize() {
   return 0;
 }
 
+// From the ObjC runtime.
+static uint8_t IS_SWIFT_STABLE = 1U << 1;
+
+LanguageType ClassDescriptorV2::GetImplementationLanguage() const {
+  std::unique_ptr<objc_class_t> objc_class;
+  if (auto *process = m_runtime.GetProcess())
+    if (Read_objc_class(process, objc_class))
+      if (objc_class->m_flags & IS_SWIFT_STABLE)
+        return lldb::eLanguageTypeSwift;
+
+  return lldb::eLanguageTypeObjC;
+}
+
 ClassDescriptorV2::iVarsStorage::iVarsStorage() : m_ivars(), m_mutex() {}
 
 size_t ClassDescriptorV2::iVarsStorage::size() { return m_ivars.size(); }

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCClassDescriptorV2.h

@@ -12,6 +12,7 @@
 #include <mutex>
 
 #include "AppleObjCRuntimeV2.h"
+#include "lldb/lldb-enumerations.h"
 #include "lldb/lldb-private.h"
 
 #include "Plugins/LanguageRuntime/ObjC/ObjCLanguageRuntime.h"
@@ -34,6 +35,8 @@ class ClassDescriptorV2 : public ObjCLanguageRuntime::ClassDescriptor {
     return true; // any Objective-C v2 runtime class descriptor we vend is valid
   }
 
+  lldb::LanguageType GetImplementationLanguage() const override;
+
   // a custom descriptor is used for tagged pointers
   bool GetTaggedPointerInfo(uint64_t *info_bits = nullptr,
                             uint64_t *value_bits = nullptr,

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

@@ -33,6 +33,7 @@
 #include "lldb/Target/ABI.h"
 #include "lldb/Target/DynamicLoader.h"
 #include "lldb/Target/ExecutionContext.h"
+#include "lldb/Target/LanguageRuntime.h"
 #include "lldb/Target/Platform.h"
 #include "lldb/Target/Process.h"
 #include "lldb/Target/RegisterContext.h"
@@ -758,6 +759,19 @@ AppleObjCRuntimeV2::AppleObjCRuntimeV2(Process *process,
   RegisterObjCExceptionRecognizer(process);
 }
 
+LanguageRuntime *
+AppleObjCRuntimeV2::GetPreferredLanguageRuntime(ValueObject &in_value) {
+  if (auto process_sp = in_value.GetProcessSP()) {
+    assert(process_sp.get() == m_process);
+    if (auto descriptor_sp = GetNonKVOClassDescriptor(in_value)) {
+      LanguageType impl_lang = descriptor_sp->GetImplementationLanguage();
+      if (impl_lang != eLanguageTypeUnknown)
+        return process_sp->GetLanguageRuntime(impl_lang);
+    }
+  }
+  return nullptr;
+}
+
 bool AppleObjCRuntimeV2::GetDynamicTypeAndAddress(
     ValueObject &in_value, lldb::DynamicValueType use_dynamic,
     TypeAndOrName &class_type_or_name, Address &address,

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.h

@@ -37,6 +37,8 @@ class AppleObjCRuntimeV2 : public AppleObjCRuntime {
 
   static llvm::StringRef GetPluginNameStatic() { return "apple-objc-v2"; }
 
+  LanguageRuntime *GetPreferredLanguageRuntime(ValueObject &in_value) override;
+
   static char ID;
 
   bool isA(const void *ClassID) const override {

lldb/source/Plugins/LanguageRuntime/ObjC/ObjCLanguageRuntime.h

@@ -23,6 +23,7 @@
 #include "lldb/Symbol/Type.h"
 #include "lldb/Target/LanguageRuntime.h"
 #include "lldb/Utility/ConstString.h"
+#include "lldb/lldb-enumerations.h"
 #include "lldb/lldb-private.h"
 
 class CommandObjectObjC_ClassTable_Dump;
@@ -84,6 +85,11 @@ class ObjCLanguageRuntime : public LanguageRuntime {
       return (m_is_cf == eLazyBoolYes);
     }
 
+    /// Determine whether this class is implemented in Swift.
+    virtual lldb::LanguageType GetImplementationLanguage() const {
+      return lldb::eLanguageTypeObjC;
+    }
+
     virtual bool IsValid() = 0;
 
     /// There are two routines in the ObjC runtime that tagged pointer clients